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Transportation Planning for Your Community - Traffic Planning
Click HERE for graphic. PREFACE This publication is part of a series entitled Transportation Planning for Your Community and is designed to acquaint officials and planners with transportation planning for communities of from 25,000 to 200,000 population. The series consists of two guides that explain the concepts of transportation planning and five technical manuals that describe techniques for carrying out transportation planning programs. The guides are: A Guide for the Decisionmaker and The Manager's Guide for Developing a Planning Program. The five technical manuals are titled: Traffic Planning Transit Planning System Planning Monitoring and Forecasting Programming Projects A Guide for the Decisionmaker describes the importance of urban transportation and the benefits of transportation planning. It includes a review of how transportation planning works, and the role of city, county and town officials in transportation planning. The Manager's Guide for Developing a Planning Program describes the principles of transportation planning and is directed to those engineers, planners and administrators who are charged with the responsibility of organizing and administering the transportation planning program. The individual technical manuals describe transportation planning techniques appropriate for small communities. The manuals also include references to other publications that describe appropriate planning techniques. The Traffic Planning manual is a reference of basic traffic engineering techniques and their potential for improving traffic flow and traffic safety of urban arterial streets and highways. The manual identifies the traffic engineering measures appropriate for consideration in development of transportation improvement plans and programs. The Transit Planning manual includes techniques for estimating transit patronage, service options, and operating requirements. Also included are procedures for evaluating the need for specialized services for the elderly and handicapped. i For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington. D.C. 20402 The System Planning manual details the steps required for the functional classification of streets and highways, the estimation of future traffic, the estimation of the impacts of future traffic, and the estimation of street and highway system requirements. An Appendix includes alternative methods for forecasting traffic. The Monitoring and Forecasting manual provides instructions for assembling inventories of transportation and land activity. It describes methods for monitoring the performance of the transportation system and general community development and methods for forecasting information needed in urban transportation planning. The Programming Projects manual contains procedures for development of the transportation improvement program. Included are procedures for identification of candidate improvement projects, determination of the plan to fund candidate improvement.projects, assignment of priorities to candidate improvement projects, budget allocation and project scheduling, and monitoring, adjusting and evaluating the programs. This series was prepared by the COMSIS Corporation and the Highway Users Federation for Safety and Mobility under a grant from the Federal Highway Administration with the aid of a "steering committee" made up of the following officials: Dan C. Dees Illinois Department of Transportation Springfield, Illinois James Echols Tidewater Transportation Commission Norfolk, Virginia David D. Grayson Automobile Club of Southern California Los Angeles, California John J. Holland Cumberland County Planning Board Bridgeton, New Jersey F.W. Landers Department of Public Works Worcester, Massachusetts Marion R. Poole North Carolina Department of Transportation Raleigh, North Carolina ii The principal investigators were: Arthur B. Sosslau COMSIS Corporation Wheaton, Maryland Marshall F. Reed, Jr. Highway Users Federation for Safety and Mobility Washington, D.C. Other principal authors were Maurice M. Carter of COMSIS Corporation and Woodrow W. Rankin of the Highway Users Federation. TABLE OF CONTENTS Page PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . 1 CHAPTER ONE: TRAFFIC ENGINEERING MEASURES TO IMPROVE FLOW . . . . 2 Traffic Flow Studies . . . . . . . . . . . . . . . . . . . . 2 Initial Problem Identification . . . . . . . . . . . . . . . 2 Improvement Measures . . . . . . . . . . . . . . . . . . . . 3 Traffic Signal Improvements. . . . . . . . . . . . . . . . . 4 Cycle Length . . . . . . . . . . . . . . . . . . . . . . . . 4 Cycle Split. . . . . . . . . . . . . . . . . . . . . . . . . 5 Turn Controls at Traffic Signals . . . . . . . . . . . . . . 5 Signal Coordination. . . . . . . . . . . . . . . . . . . . . 6 Parking Controls . . . . . . . . . . . . . . . . . . . . . . 6 One-Way Streets. . . . . . . . . . . . . . . . . . . . . . . 7 Unbalanced Flow. . . . . . . . . . . . . . . . . . . . . . . 9 Reserved Lanes For High Occupancy Vehicles . . . . . . . . .10 Access Controls. . . . . . . . . . . . . . . . . . . . . . .10 Two-Way Left Turn Lanes. . . . . . . . . . . . . . . . . . .10 Minor Physical Improvements. . . . . . . . . . . . . . . . .14 Offstreet Parking. . . . . . . . . . . . . . . . . . . . . .14 Use of Traffic Control Devices . . . . . . . . . . . . . . .16 Enforcement. . . . . . . . . . . . . . . . . . . . . . . . .16 Improvement Priorities . . . . . . . . . . . . . . . . . . .17 CHAPTER TWO: TRAFFIC ENGINEERING MEASURES TO IMPROVE SAFETY . . .18 CHAPTER THREE: VOLUME REDUCTION TRAFFIC IMPROVEMENT MEASURES. . .20 Auto Restricted Zones. . . . . . . . . . . . . . . . . . . .20 Carpools and Vanpools. . . . . . . . . . . . . . . . . . . .20 Variable Work Hours. . . . . . . . . . . . . . . . . . . . .21 Bus Lanes. . . . . . . . . . . . . . . . . . . . . . . . . .21 CHAPTER FOUR: ADMINISTRATION OF TRAFFIC PLANNING AND OPERATIONS .22 Plan Review. . . . . . . . . . . . . . . . . . . . . . . . .22 Master Street Plans. . . . . . . . . . . . . . . . . . . . .22 Subdivision Street Plans . . . . . . . . . . . . . . . . . .23 Street Improvement or Construction Plans . . . . . . . . . .23 Land Development and Improvement Plans . . . . . . . . . . .24 Traffic Control Program Review . . . . . . . . . . . . . . .27 Traffic Control Device Installation and Maintenance. . . . .28 Traffic Engineering Records and Data Collection. . . . . . .30 Accident Records . . . . . . . . . . . . . . . . . . . . . .30 Volume and Other Traffic Records . . . . . . . . . . . . . .32 Traffic Regulations Records. . . . . . . . . . . . . . . . .32 Traffic Control Device Installation and Maintenance Record .32 REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . .35 iv LIST OF FIGURES Figure Number Title Page 1 Counterclockwise One-Way Layout . . . . . . . . . . . . 8 2 Special One-Way To Two-Way Transition (Schematic-Not to Scale). . . . . . . . . . . . . . . . 8 3 Two-Way Left Turn Layout. . . . . . . . . . . . . . . .13 4 Typical Accident Location Card. . . . . . . . . . . . .31 5 Sample Work Order for Traffic Control Device Maintenance and Installation. . . . . . . . . . . . . .33 LIST OF TABLES Table Number Title Page 1 Use Warrants For Preferential Lanes . . . . . . . . . .11 2 Driveway Controls For Arterial Streets. . . . . . . . .12 3 Parking Requirements. . . . . . . . . . . . . . . . . .15 4 Minimum Geometric Design Requirements For Streets . . .25 5 Traffic Generation For Selected Land Uses . . . . . . .26 v INTRODUCTION In any community, as traffic conditions become more complex and interwoven with patterns of expansion and growth, there is a need for a continuing, comprehensive traffic engineering program. The areawide application of traffic engineering measures and use of traffic control devices following proven principles and practices can make a major contribution towards the safe And efficient movement of people and goods. The purpose of this manual is to provide metropolitan planning organization staffs a ready reference of basic traffic engineering techniques and their potential for improving traffic flow and traffic safety on urban arterials other than freeways and expressways. In addition, Chapter Four provides a description of the basic administrative framework for an effective local traffic engineering organization in a small urban area. This manual is not a handbook or guide for the application of traffic engineering measures, as that is the job for a traffic engineer. As a planning tool, the manual is intended to assist in the identification of traffic engineering measures appropriate for consideration in the development of a community's transportation improvement program or plan. The range of the potential improvement in traffic flow or safety is given for many measures. These benefits are representative of what has been achieved and they are adequate for preliminary planning purposes, but they will not be achieved every time the measure is used. An engineering analysis is needed to evaluate the probable benefit of each application under consideration. As part of the planning program for improving the quality and safety of traffic operations, an analysis of proposed improvement measures by a professional traffic engineer is essential. This engineering study is needed to determine if a proposed measure is appropriate for the location under consideration and to evaluate what its probable benefits will be. An engineering study is also needed to develop the detailed design or plan for the application of measures scheduled for implementation. The primary purpose for implementing a traffic improvement measure may be either to improve traffic flow or to improve traffic safety, but both objectives should be realized to some degree for any measure. However, the criteria for initial identification of the problems are different for each purpose and the concepts and basic procedures of each will be discussed in this manual. When traffic studies are referred to in this manual, details of the study methods are not described. Readily available references covering the procedures are identified. Where appropriate, technical terms are defined in footnotes. 1 CHAPTER ONE TRAFFIC ENGINEERING MEASURES TO IMPROVE FLOW The first step in identifying traffic engineering measures appropriate for consideration in the development of a community's transportation improvement program is the collection of current information on traffic flow. This information must be in sufficient detail to provide a picture of the quantity, distribution and quality of traffic flow in the area. Most of this information is obtained from volume counts and traveltime studies. It is used both to identify problem locations and to determine improvement measures that merit consideration for use at those locations. TRAFFIC FLOW STUDIES A major traffic count program is needed to determine the quantity and distribution of traffic. At a minimum, volume counts should be made on typical week days from at least 7 a.m. at the following locations: 1. Where major highways enter the community; 2. At all signalized intersections; and 3. At other locations,where changes in traffic volume may be significant, such as industrial parks and major shopping centers. "Floating car" traveltime studies can be used for assessing the quality of traffic flaw in the urban area. At a minimum, they should be made to determine the average peak and offpeak traveltimes and points of delay for each major arterial street. Procedures for making areawide volume and "floating car" traveltime studies and organizing the information collected for analysis are given in the Manual of Traffic Engineering Studies 1/ published by the Institute of Transportation Engineers. Often, you can use traffic information collected by the State highway agency for the roads and streets for which it is responsible in your community. Citizen complaints and police reports on traffic problems are another source of information on locations where congestion and delay are a problem. A screening of those reports can identify locations where an onsite observation should be made to determine the size of the reported problem. The information collected in traffic flow studies and from investigations of congestion reports will help identify specific locations that merit further study. The study should be used to make an initial identification of the type of problem responsible for traffic delay. INITIAL PROBLEM IDENTIFICATION The degree of traffic congestion severity, particularly during peak periods, is relative to city size. But if traveltime on an arterial street is over 25 percent more in the peak periods of an average week day than in the offpeak periods, it is generally accepted that the arterial is congested and has an unsatisfactory level of service. 2 The congested sections of an arterial with excessive peak hour traveltimes can be identified from the information collected in the "floating car" traveltime study. The congestion may be due to intersection problems, midblock problems, or both. Detailed, onsite studies of the location are then required to make a preliminary identification of the causal factors of the congestion. Some traffic delays can be expected at intersections with traffic signals. However, if the delay is such that vehicles have to wait through more than one green light before clearing the intersection, the location is considered congested. The congestion often is related to the operation of the traffic signal. Procedures for analyzing traffic operations at a signalized location are discussed in the Traffic Signal Improvements section of this manual. Unnecessary stops or slowdowns at midblock locations not associated with backups.from traffic signals are symptoms of inadequate street capacity or excessive interference from vehicles entering or leaving driveways. Depending on lane widths, mix of truck and automobile traffic, and other factors, the capacity of a lane of traffic between intersections on a two-way arterial street ranges from 500 to 800 vehicles per hour. When traveltime studies show that an arterial street is congested and lane volumes on the street are over 500 vehicles per hour in the peak hours, traffic control improvements such as parking controls, one-way streets, unbalanced flow, and lane use controls should be considered as possible improvement measures. Preliminary studies should be made to determine whether or not such improvements merit further consideration. Procedures for making a preliminary evaluation of the potential benefit of improvements are described in subsequent sections of this manual. IMPROVEMENT MEASURES The following traffic engineering measures to improve flow may have an application: Traffic signal improvement Parking controls One-way streets Unbalanced flow Reserved lanes for high occupancy vehicles Access controls Two-way left turn lanes Minor physical improvements 3 Although it is not possible to state unequivocally which traffic engineering measure will provide the best solution for a specific problem, some general guidelines apply. In most communities, measures to improve operations at traffic signals, including turn controls, should be considered first. Next, parking prohibitions should be considered. The other measures, many of which require unique conditions for successful use, have less general application. Because police enforcement generally is needed for the effective implementation of most traffic, control measures, the availability of police must be realistically considered before advocating such a measure. Traffic Signal Improvements At a good traffic signal installation where there are normal volumes of right and left turns, each straight through lane on the major street can be expected to carry volumes of between 450 and 650 vehicles per hour. However, poor traffic signal design or operation can substantially reduce this potential traffic capacity and can be a cause of traffic delay. Four major causes of this delay are: Improper cycle length* Improper cycle split** Left turn movements Lack of coordination of traffic signals Often, more than one of these factors may affect traffic operations at an intersection. The engineering study of a congested signal location will identify the causes of the delays and the corrective measure that is most likely to be effective. Cycle Length - An improper cycle length is a frequent cause of delays at traffic signals. A cycle that is too long is inefficient because there will be periods when the full length of the green time*** is not used on one or more approaches. A cycle that is too short causes too many "start up" delays for vehicles moving through the intersection. Although some cycle length adjustment can be made for any traffic signal, providing cycle length flexibility to meet the varying traffic loads during peak and offpeak periods may require additional signal control equipment. ___________________________ * Cycle length - The length of time between the start of successive green signals on any approach to the signal. ** Cycle split - The percent of the total cycle time given to each traffic movement at the signal. *** Period when green signal indication is illuminated. 4 Cycle Split - Green time is also wasted when the cycle split is not correctly related to the distribution of traffic on the streets approaching a traffic signal. If the distribution is reasonably constant for most of the day, a cycle split correction can be made without a major change or addition to the traffic signal control equipment. However, equipment improvements may be required to provide cycle split flexibility to accommodate the usual variations in traffic at peak and offpeak periods. The fluctuations in traffic volume that create the cycle split and cycle length problems are most pronounced between peak and offpeak traffic periods. If observations of traffic movements at signal locations during these periods show that there is a disproportionate amount of backup on any approach during most signal cycles, an engineering study of the location should be made to determine what adjustments in cycle length or cycle split are needed to correct this cause of traffic congestion. Cycle split and cycle length problems are one of the most common causes of signal intersection delay. Preliminary studies to determine if split and length are problems should be one of the first steps in a traffic signal improvement study. Turn Controls at Traffic Signals - Turning movements, particularly left turns, are another cause of delay at traffic signal locations. In general, left turns up to 15 percent and right turns up to 20 percent of the through traffic are considered normal. When turns exceed these normal limits, congestion may develop because of backups of traffic behind vehicles waiting to make a turn. Minimizing left turn delays may be relatively easy or it may require a major physical improvement. Where left turns are a relatively minor movement, they may be prohibited. A factor to be considered in evaluating whether to prohibit left turns is the availability of alternate locations for the turning movements and the impact on traffic of the turns at the alternate locations. Special or exclusive left turn signal phases may be installed. These special turn phases should be limited to locations where there are special lanes for left turns. In addition, the special phases can reduce the efficiency of traffic operation in proportion to the percent of the total "green time" they require. Even though they speed up left turn movements, their total impact on traffic operations should be fully evaluated. Where there is adequate street width, or where widening is possible, a special left turn lane may be the answer. Consideration of this type of improvement should be limited to locations where there is sufficient distance in advance of the intersection to provide an adequate turn lane. This type of turn control should be considered only where the volume of turns justifies a priority turn phase in the signal cycle. Delays from very heavy left turn movements often can be minimized by permitting left turns from the special turn lane and the lane immediately adjacent to it. For such locations, two-lane left turn controls can double the turning capacity with only a minor loss of straight-through capacity. 5 Signal Coordination - Where traffic signals are located less than one-half mile apart along an arterial route, they should be electrically coordinated to promote uninterrupted movement of through traffic. In addition, coordination of signals up to one mile apart along an arterial route should be considered when vehicle traveltime between signals is approximately one and one- half signal cycles. Some factors which limit the effectiveness of traffic signal coordination are: block length; amount of turning movements; the relationship of a street's capacity to its volume; truck movements; pedestrian crossings; and the number and spacing of arterial intersections. However, studies have shown that coordinated signals have reduced vehicle delay by as much as 70 percent. On arterials where surveillance has shown slow traveltimes and frequent stops for traffic signals, studies should be initiated to determine how signal coordination can be achieved where it does not exist, or be improved where it is being used. Parking Controls The capacity of a normal lane of traffic be-tween intersections on a two-way arterial street ranges from 500 to 800 vehicles per hour. On such an arterial where parking is permitted, a parking and loading prohibition during peak traffic periods should be considered. On arterials where the peak flow is inbound on one side in the morning and outbound on the other in the evening, a peak-hour restriction on the side of the street carrying the peak flow is usually all that is required. In the initial review of proposals to restrict curb use the following questions should be considered: - What will be the capacity gain? - Can adequate provision be made for the safe transition of traffic at the end point of the restricted zone? - Are there acceptable alternate locations for parking? - Are there acceptable alternate locations or other provisions for curb loading and unloading? - For what hours of the day will the regulation be needed? - Can the proposed regulations be enforced? If the parking restriction will provide an adequate lane for traffic, a capacity gain at the low end of the 500 to 800 vehicles per hour volume can be expected, because traffic in the curb lane is subject to a maximum interference from turning movements and entering traffic. If the parking restriction will not provide sufficient width for an additional lane of traffic, the elimination of curb parking will improve the traffic flow and the capacity in the lane closest to the curb. The added width will improve the movement of buses into and out of bus stop areas, and minimize traffic slowdowns behind right turning vehicles. 6 If angle parking is currently permitted on arterials, its conversion to parallel parking should be considered. Although angle parking provides approximately twice as many parking spaces per block length as parallel parking, it uses more than twice as much of the street width and its accident potential is from three to five times as great as parallel parking. To generate public support, curb parking should be prohibited only during those hours when the added street width is needed to improve traffic flow. If heavy traffic volumes are sustained from the a.m. peak period through the p.m. peak period, parking should be prohibited for the entire period. If a peak hour or an all day curb parking prohibition is to be effective, police enforcement is essential. The benefits of parking prohibitions will be negligible without a high level of enforcement coupled with a policy of towing away illegally parked vehicles. Where a surveillance study shows that additional lanes for traffic are needed on the approaches to intersections, parking bans can improve traffic movement. It also will improve bus operations into and away from the curb. One-Way Streets One-way traffic movement can be expected to improve the capacity of a pair of arterial streets by 20 to 50 percent because turn delays are minimized. One-way movement also facilitates coordinated signal control and usually reduces traffic accidents. Two conditions should prevail before a one-way street plan is implemented. They are: (1) Generally, the one-way pair should not be more than 600 feet apart. (2) At the terminal points of the one-way pair, the transition to and from two-way traffic should provide safe operation with minimum delay. Spacing a one-way pair more than 600 feet apart increases out- of-the-way travel and therefore decreases the efficiency of the community's street system. To smooth the transition from one-way to two-way operation, the traffic flow on one-way streets should be counterclockwise, as shown in Figure 1. Traffic will therefore move from one-way to two- way operation, and vice versa, without crossing conflicts. Traffic controls should be established at the transition point from one-way to two-way operation to give priority to the necessary right and left turn movements. For a major one-way pair of considerable length and serving a substantial amount of traffic, consideration should be given to the construction of short, new sections of street to provide for a free moving transition as shown in Figure 2. This is particularly worthy of consideration if one street of the one-way pair carries most of the traffic beyond the one-way section. 7 Click HERE for graphic. Figure 1 COUNTERCLOCKWISE ONE-WAY LAYOUT Click HERE for graphic. Figure 2 SPECIAL ONE-WAY TO TWO-WAY TRANSITION (Schematic Not to Scale) 8 The one-way street plan must be carefully worked out in advance in consultation with residents and businesses abutting the streets. One-way street plans also must be reviewed in advance by police and fire officials to determine whether or not the plan will adversely affect emergency response capabilities. One-way streets may reduce the level of business for some types of commercial activities such as those with a large amount of customer pickup or dropoff business. Often some objections to one-way streets can be eliminated by the reinstatement of curb parking on at least one side of the one-way street. Where there is a heavy peak-hour directional traffic flow on a major arterial that is parallel to an arterial with little or no reverse traffic flow during the peak period, consideration should also be given to establishing a "non-paired", peak-hour one-way traffic flow on the major arterial. If the reverse flow can be accommodated on parallel arterial or collector streets without undue congestion or excessive out-of-the-way travel, a "paired" system need not be established. Part-time, one-way streets require considerable advance publicity and thorough advance planning for signing and other traffic control devices. Unbalanced Flow For wide arterial streets an unbalanced traffic lane plan is a possible alternate to a one-way street plan. In an unbalanced traffic lane plan, the center lane or lanes are specifically marked for use by traffic travelling in the direction of the heavy traffic flow. For example, on a five lane street an unbalanced flow of three lanes for the heavy directional flow and two for the light flow could be established by designating the center lane as inbound from 6:00 a.m. to 9:00 a.m. and outbound 3:00 p.m. to 6:00 p.m. At other periods of the day the center lane could be designated for either inbound, outbound, or as a two-way left turn lane,* depending on the specific traffic demands of the street. Unbalanced flow with reversible lane operations can be developed for streets with three or more lanes. The number of reversible lanes, the time periods, and the offpeak use of the reversible lanes should be tailored to the specific traffic demands of the street under study. Each reversible lane in an unbalanced flow setup increases the capacity in the direction of the major flow by 500 to 700 vehicles per hour. Unbalanced flow using reversible lanes has resulted in a 15 to 20 percent reduction in traveltime. The Manual on Uniform Traffic Control Devices 2/ specifies the traffic control devices to be used to designate unbalanced flow operations. At a minimum, the unbalanced flow requires special pavement markings. In addition, to further assure safety many agencies supplement the basic traffic control devices with overhead lane signals clearly indicating which lanes are open and which are closed to traffic in each direction. Although overhead lane signals increase the cost of the improvement, they provide a positive method for indicating the unbalanced flow operation thereby enhancing the effectiveness and safety of the traffic control measure. ___________________________ * Two-way left turn lane -- see section of this manual on subject. 9 Reserved Lanes for High Occupancy Vehicles Reserved lanes for high occupancy vehicles -- buses, carpools, and vanpools have been an effective method for improving the passenger carrying capacity of street systems. However, reserving lanes for buses is limited to communities where there are heavy peak hour movements of buses. Reserving lanes for carpools and vanpools is limited to those arterial streets that serve major employment centers, where there is a potential for the development of substantial ridesharing. A basic criterion for establishing a preferential lane is that the lane must carry at least as many persons as the adjacent non- preferential lane. Warrants for preferential lanes have been developed and are shown in Table 1. If a preferential lane is not expected to carry the minimum amount of bus or ridesharing vehicle traffic, implementation of the measure should not be considered. Access Controls Although access to abutting property generally is permitted from arterial streets, sometimes it is necessary to regulate or control the turning movements into or out of the property in order to minimize their interference with traffic on the arterial. These turning movements generally are controlled by regulating the spacing, length, and curb return radii of driveways. The controls, which usually require local enabling legislation to implement, should be used whenever street improvements are made that include the construction or reconstruction of curb, gutter and driveway sections along an arterial. Suggested minimum controls are given in Table 2. Additional information on 4/ this type of control is given in A Survey of Urban Arterial Design Standards 4/ and in many State and municipal street design standards. If the left turns into or out of driveways are a major cause of congestion or accidents, it may be necessary to prohibit such turns. The prohibition can be established by regulation. However, for full effectiveness, a median barrier is required. The barrier may be a curbed median, a guardrail, or a similar device. When a barrier control is considered, advance studies of the impact on the abutting property should be made. In addition, the abutting property owners should be informed of the measure and the alternatives, such as mid-block U-turn locations, to insure adequate access to their property. Two-Way Left Turn Lanes Where street width and other physical conditions permit its use, establishing a two-way left turn lane throughout the block can minimize the traffic delay and hazard of mid-block left turns and eliminate the need for their prohibition. Two-way left turn controls should be considered only for arterials with a minimum of five traffic lanes. A typical layout is shown in Figure 3, where the center lane is designated as a two-way left turn lane and its use restricted to left turning vehicles. A two-way left turn lane requires special pavement markings and signs. The standards for these are given in the Manual on Uniform Traffic Control Devices. 2/ 10 Table 1 USE WARRANTS FOR PREFERENTIAL LANES Bus Lanes* Average Bus Buses Per Hour Passenger Freeways Arterials Loading Main Line Metered Ramp Outlying CBD 40 40 10 25 20 25 64 18 40 32 Car/Van Pool Lanes* Pool Vehicles Required Per Hour Occupancy Freeways Arterials 2 or more 750 450 3 or more 525 310 ___________________________ * Where a preferential lane is to be used by car/vanpools and buses, a combination of these warrants that reflect the probable mix of the vehicles using the lane is appropriate. Source: Levinson and Hoey, "Optimizing Bus Use on Urban Highways," Transportation Engineering Journal, (New York, American Society of Civil Engineers). 11 Table 2 DRIVEWAY CONTROLS FOR ARTERIAL STREETS Width at property line 35 Ft. Maximum Curb return radii 15 Ft. Minimum Length of tangent curb between drives 20 Ft. Minimum Distance from intersection curb return 20 Ft. 12 Click HERE for graphic. Figure 3 TWO-WAY LEFT TURN LAYOUT Source: Superintendent of Documents, Manual on Uniform Traffic Control Devices, (Washington, D.C., U.S. Government Printing Office, 1978) 13 Minor Physical Improvements Minor physical improvements such as widening of the approach to an intersection and intersection channelization can make a major contribution to improved traffic flow on arterials. Channelization can range from the installation of a single small traffic island to provide for a continuous right turn at a major intersection to the installation of several curbed or painted islands to promote the orderly flow of traffic through a complex intersection. The need for this type of improvement is indicated by accident report information, observation of the flow of traffic through the intersection, and police and citizen reports of confusing traffic flows. At intersections where surveillance studies have shown there are delays due to either right or left turning vehicles, a possible solution is the provision of a special turn lane by widening the intersection approach. Depending on the existing street width and other physical conditions, a 10 to 12 foot widening is usually needed for this type of improvement. The analysis for a proposed intersection widening should determine whether or not it will expedite traffic flow without impairing traffic safety. OFFSTREET PARKING Adequate parking is an essential element of an urban area's street transportation system. Some of this parking is provided at the curb. However, as traffic growth on major streets requires more street capacity, more of the necessary parking is supplied privately by parking facilities. Most zoning regulations specify the amount of parking to be provided by new developments, particularly those outside of the developed business district (Table 3). However, many cities have found it necessary to have offstreet parking facilities in the Central Business District that serve a group of the businesses or commercial developments in that area. To provide this parking, each community must decide the type of parking program most suitable to its particular need. The parking can be supplied by private development, or it can be supplied by a public agency or parking authority. Local practice, patterns of business, the size of the community, the magnitude of the parking demand and other factors will influence which type parking policy a city follows. Regardless of the type of parking program a city chooses to use, the principal official concern should be to develop a supply of offstreet parking that will best serve the community not on who will 'provide and operate the facilities. The primary parking program responsibility of municipal government should be program administration. Proper administration is essential if the parking program is to be coordinated with the transportation and other development programs in the community. In addition, a community parking program should not be oriented to the needs of only one particular area of the community. It should consider all parking needs and include them, if appropriate, in a comprehensive program. 14 Table 3 PARKING REQUIREMENTS TYPE OF LAND USE SPACES REQUIRED Retail Store (Not in a 1 per 350 sq. ft. G.F.A.* Shopping Center) Office Building 1 per 300 sq. ft. G.F.A. Restaurant 1 per 4.5 seats (sit down type) Single Family Dwelling 1.75 per Unit Multi-Family Dwelling 1.75 per Unit Shopping Center 7 per 1,000 sq. ft. G.F.A. (25-75,000 sq. ft. G.F.A.) Industrial Plants Heavy Manufacturing 1 per 900 sq. ft. G.F.A. Medium Manufacturing 1 per 450 sq. ft. G.F.A. * G.F.A. Gross floor area. Source: Highway Users Federation, Engineering For Traffic In A Small City, (Washington, D.C. 1970). 15 Parking program development is a complex subject, and most communities have relied on engineering studies for the basic assessment of their needs and recommendation for the types and locations of facilities to meet those needs. Because of the many options that are available for funding, developing, and operating parking facilities, decisions on the type of program to be implemented, if any, should be made by local officials who have thoroughly familiarized themselves with the options. A basic initial reference for local officials considering parking program development is Parking Principles.5/ This Special Report of the Transportation Research Board covers all aspects of municipal parking. It provides information on the following subjects: parking characteristics, parking and zoning, parking programs, location and design of parking facilities, parking- facility operation, transit and parking, and curb parking. The coverage is in sufficient detail to provide the essential introductory information that a public official would need to initiate the planning of a municipal parking program. USE OF TRAFFIC CONTROL DEVICES Proper use of traffic control devices often can improve the flow of traffic along an arterial street. For example, advance mid-block street name signs can be used at major intersections so drivers planning to turn will have time to move to the right or left lane. Stop signs on all the approaches to arterial streets can insure the priority movement of traffic along the arterial. Uniformly located, readily visible signal indications for all movements of traffic at traffic signals will minimize driver confusion and expedite traffic flow. When traffic volume increases it is necessary to establish new traffic control measures at some locations and revise or change the control at others. The addition of these new controls or the revision of existing controls are an essential part of the traffic engineering improvement program in any urban area. Traffic signals and stop and yield signs are the controls generally installed or modified in this type of a program. Their correct use in this type of a program can contribute to good traffic flow despite increased volumes. The Manual on Uniform Traffic Control Devices 2/ (or a comparable State manual) provides the basic warrants and installation standards for all traffic control devices. The standards and warrants of the Manual should be considered the minimum requirements for installation or modification of devices. ENFORCEMENT Where a traffic surveillance study indicates that disregard of parking and other traffic regulations seriously congests traffic operations, a stepped-up enforcement effort often can be the most effective traffic flow improvement. On arterials with parking restrictions opening curb lanes for traffic by eliminating illegal parking in restricted zones can help reduce congestion. In addition, violations of peak hour parking bans, and parking in, or too close to, bus stops can be a major cause of delay for transit operations. Enforcement 16 of parking regulations should be given a high priority in considering traffic improvement measures. Violations of left turn prohibition also can be a major cause of traffic congestion and should be identified and corrected through enforcement. The effective use of enforcement personnel in improving traffic operations can be expected only if the enforcement agency or agencies are a party to the traffic improvement planning. Their input can be most useful in developing a total plan. IMPROVEMENT PRIORITIES At any one time a community will have a considerable number of potential traffic engineering improvement projects. Generally, there are more projects than can be funded. Some basis for determining a priority ranking for the projects is needed. There is no generally accepted priority ranking system for traffic engineering improvement projects. However, in a determination of which projects will be funded, several factors should be considered. One is the relative level of congestion for the location or road section covered by the project. For specific locations, such as an intersection, the level or quality of traffic service can be measured by the ratio of the volume at the location compared to the street capacity available to handle that volume. The Highway Capacity Manual 6/ describes how volume/capacity ratios are calculated. Overall traveltime and number of stops is the usual measure of the quality of traffic flow for sections of an arterial street. In addition, because most traffic engineering measures will result in an improved level of traffic safety, the need and potential of the safety improvement is a factor that should be considered. Procedures for ranking safety hazards are given in Chapter Two. The factors discussed above do not provide a numerical rating for ranking projects, but they do provide an indication of the relative significance or need for the improvement at a particular location. They should be a basic input to the determination of which projects will be given the highest priority. 17 CHAPTER TWO TRAFFIC ENGINEERING MEASURES TO IMPROVE SAFETY Properly applied traffic engineering measures-can make a substantial contribution to a reduction in traffic accidents and their severity. Traffic Control and Roadway Elements 7/ is a basic reference on the relationship between traffic control and safety. The use of traffic engineering measures for improving identified high hazard intersections or street sections should be a major component of a community's street improvement program. A prerequisite of a traffic engineering safety improvement program is the availability of complete, accurate, 'adequately referenced, and readily accessible accident data and current traffic volume information for the arterial street system. Basic record systems to meet these needs are described in Chapter Four. Using the data in those record systems, a traffic-volume- based-accident rate comparison of high accident locations can be made using established procedures 8/ Such accident location comparisons provide a priority ranking of the identified high hazard locations that eliminates the bias of high volume locations. It provides a representative measure of the relative safety hazard at high hazard locations and can be used in initiating engineering studies of those locations and the programming of improvements. The installation of a traffic signal is probably the most frequently proposed improvement for a high accident location. In some cases, however, total accidents increase because of the increase of minor, rear end collisions. Nevertheless, there will be a reduction in the more severe head-on or right angle accidents thereby reducing accident severity. The upgrading or modernization of existing signal installation, particularly those that have marginal compliance with current standards, can result in an improvement in traffic safety. Such signal modernization, particularly when it provides improved visibility of the signal indications, has resulted in accident reductions ranging from 20 to 50 percent. At locations where left turns are identified as a significant accident causal factor, left turn prohibitions or special lanes for turning vehicles can reduce the potential of conflicts between the turning and through traffic and reduce the potential for accidents. Turn prohibitions have achieved accident reductions ranging from 40 to 60 percent. The provision of a special lane for left turns has resulted in accident reductions ranging from 20 to 50 percent. For mid-block left turn accident problems, properly used two-way left turn lanes (see Chapter One) have resulted in accident reductions ranging from 30 to 45 percent. Intersection channelization, which provides controlled, minimum conflict travel paths for vehicles through complex intersections, can improve both traffic safety and traffic flow. This type of improvement is frequently used to reduce the accident potential at complex, multiconflict intersections. Accident reductions of over 30 percent have been reported for these types of improvements. 18 Although one-way streets are seldom implemented solely for the improvement of traffic safety, traffic operations on one-way streets have less potential for conflicts and generally a better safety record. Reported safety improvements after the changeover from two-way to one-way traffic range from five percent to over 30 percent. However, often in the early stages of one-way operation, before drivers become accustomed to the one-way control, accidents may increase temporarily. This safety problem can be minimized, if not eliminated, by a major, well organized education campaign for both drivers and pedestrians prior to establishing one-way streets and in the early months of their operation. Sometimes traffic safety improvement measures can be incorporated or included in projects primarily developed to improve traffic flow. However, the importance of improved traffic safety will justify the programming of safety projects as a separate category in the street improvement program. The above mentioned traffic-volume-based-accident-rate comparisons provide the basis for assignment of project priorities. 19 CHAPTER THREE VOLUME REDUCTION TRAFFIC IMPROVEMENT MEASURES Measures that are intended to reduce the number of vehicles on arterial streets during peak-hours may be appropriate for consideration in a community's traffic improvement plan. The principal measures in this category are: increased ridesharing (carpooling and vanpooling), staggered or flexible work hours, and enhanced transit service. In some cases these measures may be counterproductive of each other. For example, increased carpooling and vanpooling may have an adverse impact on transit use. Similarly, a program of staggered work hours may minimize opportunities for car and vanpool development and limit the attractiveness and utility of peak-hour- express bus service. The potential of the adverse impact of one program on the effectiveness of another must be recognized and evaluated in the planning of volume reduction traffic improvement measures. AUTO RESTRICTED ZONES The prohibition or restriction of private automobile traffic from specific areas, usually referred to as auto restricted zones (ARZ), is a transportation systems management measure that has been used in some communities. Basically, it is intended to maintain or revive the economic vitality of a central business district. In addition, these zones often include measures to expedite the movement of buses through or around the special zone. Because an improperly developed ARZ can have a major adverse impact of the traffic that is restricted from the zone, planning for this type of measure must include a complete traffic analysis. It should include a full evaluation of the impact of the measure on all types of traffic and the effects the restriction of travel will have on the economic activity of the entire community. A basic consideration prior to implementing any restricted zone should be a determination that the zone will not result in a degradation in the quality of the overall traffic movement in the urban area. CARPOOLS AND VANPOOLS Experience has shown that carpool and vanpool ridesharing programs can be implemented in employment centers where there are over 200 employees working for the same basic period of the day. However, without incentives for participation, successful programs may not be achieved. Priority parking locations for ridesharing vehicles is a common incentive provided by employers. Reduced commuting costs for participants is an obvious incentive but often it is one that requires an education program for potential ride-sharers. References describing in detail the promotion and administration of ridesharing programs are available from State transportation and energy agencies or the U.S. Department of Transportation. 20 VARIABLE, WORK HOURS With variable or flexible work hours, the a.m. and p.m. commuter traffic load is spread out over a longer period of time. The resulting reduction in traffic demand can result in reduced congestion and delay. Generally, this type of program should not be considered except for work centers where there are at least 75 to 100 employees. A reference that provides guidelines for assessing the potential for variable or flexible work hours and administering such programs is Flexible Work Hours: Implications for Travel Behavior and Transport Investment Policy. 9/ BUS LANES Where warranted, exclusive or reserved lanes for buses contribute to the improvement of transportation in a community.* Service improvements such as a 15 to 30 percent reduction in bus travel time have been reported for this type of preferential treatment for transit vehicles. Because these traveltime improvements are An inducement for commuters to shift from private automobiles to transit, the implementation of express bus service and exclusive lanes can reduce peak-hour traffic loads. Factors in assessing the potential of exclusive bus lanes are: 1. The density of relatively long distance trips in an arterial corridor of an urban area, 2. The total number of trips in the corridor with a destination in a relatively small area such as the central business district, 3. The potential for developing a limited number of common origin points for inbound trips in the corridor, and 4. The potential for supplying an adequate amount of "park and ride" parking. In addition, reserved lanes require an intensive and usually continuing enforcement effort by the police if they are to be effectively utilized. Planning to provide this enforcement is an important part of the development of a reserved lane for bus operation. ___________________________ * Guidelines for the minimum transit usage that warrant consideration for the establishment of preferential transit lanes are given in Chapter One of this manual. 21 CHAPTER FOUR ADMINISTRATION OF TRAFFIC PLANNING AND OPERATIONS If a community is to have a continuous and effective program to improve traffic operations, each jurisdiction must have administrative controls and procedures to assure that the street system is planned, designed, and operated to maximize safety and efficiency. These controls and procedures can be divided into four categories: - Plan review - Traffic control program review - Traffic control device installation and maintenance - Traffic engineering data collection and record keeping As all of the categories are closely related, they should be administered on a consistent, coordinated basis. This can be achieved if responsibility for all of the elements is assigned to a single official within each jurisdiction, preferably the one responsible for public works or street engineering. This administrative organization also supplies technical support for the community's transportation planning program and will assure the effective implementation of improvement programs developed through the planning program. If such an administrative structure is lacking, its organization should be encouraged and supported as part of the community's transportation planning program. PLAN REVIEW Traffic adequacy reviews are essential for four types of plans: - Master street plans - Subdivision street plans - Street improvement or construction plans - Land development or improvement plans Master Street Plans Although the master plan for the community will be developed by the transportation planning organization, the local official in each jurisdiction responsible for traffic operations should be a participant in the planning program. Not only will this official's knowledge of current traffic operations be useful in developing master street plans, but he or she will be useful in implementation of the plans. In addition, the planning of traffic control device improvement programs and implementation of major traffic control programs should be coordinated and compatible with the proposed master street plan. 22 Subdivision Street Plans The street layout that is planned for a subdivision will have a major influence on future residents. If street layout is to be beneficial, four objectives must be considered. They are: - Vehicular Safety and Pedestrian Safety - Efficiency of Traffic Service - Liveability or amenities -- especially as affected by the street system - Economy -- in both construction and use of land as affected or related to the street system To achieve these objectives, a number of factors should be considered in the street layout and the review of the street layout. They are: 1. Local streets should be designed to minimize through traffic movement. 2. Local streets should be designed for relatively uniform low volumes of traffic (approximately 1,000 vehicles per day). 3. Local streets should be designed to discourage excessive speeds. 4. The number of intersections should be kept to a minimum. 5. The minimum angle of any intersection should be 75 degrees and most intersections should be at, or close to, 90 degrees. 6. Extensive use should be made of T intersections, offsetting them at least 150 feet. 7. The traffic movements on local streets should be set up so they do not detract from the efficiency of operations on adjacent arterial streets. 8. In order to provide efficient and safe operations extensive reliance should not be placed on traffic regulations and traffic control devices. 9. Local streets should be related to topography from the standpoint of both economics and amenities. 10. Where appropriate, in large subdivision areas, provisions for transit service should be provided in terms of adequate street widths and efficient circulation. Street Improvement or Construction Plans A traffic adequacy review should be an established procedure in the development of street improvement and construction plans. If an improvement is to provide immediate and continuing safe and efficient traffic operations, it must be built with geometric design and cross section features which are correctly related to the traffic function of the street. In addition, plans 23 and specifications for street improvements must include procedures and controls which will insure the safe and efficient handling of traffic in and around construction areas. Key items in the cross section and geometric design review are lane widths, number of lanes or pavement widths, use of median and median widths, and corner radii. Suggested minimum standards for each of these items for each class of street are given in Table 4. An important and often ignored element of traffic review of street construction and improvement plans is an evaluation of the adequacy of the provisions for the safe and efficient movement of traffic through or around the construction area. This review is equally important for other major work activities in streets such as pavement cuts, utility repairs and installations, and street maintenance. In advance of any of these activities, provision must be made for establishing adequate traffic control measures. This should include the following: 1. Requirements in the plan or other contract documents for installation and maintenance of standard construction area signs and other traffic control measures where applicable. 2. Identification of the official or agency responsible for the regular inspection of construction traffic control measures. 3. Work scheduling requirements that minimize the impact of construction, maintenance, and other in-street work on peak-hour traffic movements. Detailed standards for construction site traffic control, including signs, lights, and other devices, are given in the Manual on Uniform Traffic Control Devices. 2/ Land Development and Improvement Plans Any change in land use can change the traffic generating characteristics of an area; therefore the probable effect of plans and proposals for such changes should be evaluated. The review should provide the answers for two basic questions: - Will the new development create congestion or unsafe conditions on adjacent streets? - Will the new development have adequate offstreet parking? Most small individual lot developments will not generate sufficient traffic to create capacity--related congestion. However, this may not be true for shopping centers, food and convenience stores, drive-in restaurants, industrial plants, and office buildings. Because of the many variables affecting traffic generation, there are no standard values for the various types of land use. However, Table 5 lists typical values for the amount of traffic which five types of land use and representative types of residential development have generated during the evening peak traffic hour. 24 Table 4 MINIMUM GEOMETRIC DESIGN REQUIREMENTS FOR STREETS DESIGN FEATURE CLASS OF STREET Arterial Collector Local Number of Traffic Lanes 4-6* - - Lane Width 11-12 ft. - - Pavement Width 36-40 ft. 27-34 ft. Median Divider Yes Rarely Rarely Median Width 16 ft. - - Corner Radii 25-30 ft. 25 ft. 20 ft. ___________________________ * The provision of adequate capacity for future traffic volumes should be * major determining factor for this design element. The range in the volumes from one direction that can be expected to move through signalized intersections (the usual restriction points on arterial streets) without excessive delay for two typical street widths under normal traffic conditions are: With no approach parking 72 feet (6 lanes) - 1,450 to 1,700 vehicles per hour 48 feet (4 lanes) - 950 to 1,150 vehicles per hour With approach parking 72 feet (6 lanes) - 1,050 to 1,250 vehicles per hour 48 feet (4 lanes) - 750 to 900 vehicles per hour These values are for locations with less than 10 percent turns, low pedestrian volumes, less than 10 percent trucks, no buses, and 50 to 60 percent of the signal time given to this arterial movement. Source: Highway Users Federation, Engineering For Traffic In A Small City, (Washington, D.C., 1970). 25 Table 5 TRAFFIC GENERATION FOR SELECTED LAND USES TYPE OF LAND USE P.M. PEAK-HOUR TRIPS Shopping Center 25-75,000 sq.ft. G.F.A. 15 per 1,000 sq.ft. G.F.A. Food or Convenience Store 1,000-10,000 sq.ft. G.F.A. 20 per 1,000 sq.ft. G.F.A. Drive-in Restaurants 100 per 1,000 sq.ft. G.F.A. Industrial Plants Heavy Manufacturing 1 per 1,000 sq.ft. G.F.A. Medium Manufacturing 2 per 1,000 sq.ft. G.F.A. Office Buildings 2 per 1,000 sq.ft. G.F.A. Residential Suburban Single Family 1 per dwelling unit Suburban Multi-Family 0.7 per dwelling unit Mobile Home Park (Non transient) 0.7 per dwelling unit * G.F.A. -- Gross Floor Area Trip -- A single vehicle trip either in or out ___________________________ Source: Highway Users Federation, Engineering For Traffic In A Small City, (Washington, D.C., 1970). 26 The ability of a new development to receive and store the traffic it generates can be a critical aspect of its impact on adjacent street operations. In the review of any new development, several items should be checked to evaluate the site and access planning in relation to the quality and safety of traffic flow on adjacent streets. Sufficient spaces should be provided to accommodate the expected peak demand for parking. Representative figures of the parking demand for several common types of land use in jurisdictions with relatively high automobile use are given in Table 3. Poorly designed access and inadequate interior traffic circulation of a new development can cause traffic congestion; therefore those aspects of the site plan should be reviewed. Driveways should be designed so movement into or out of the property they serve can be made with a minimum interference to traffic. Flat grades and angles and wide radius curb return are desirable. However, studies have shown that uncontrolled access or excessively wide drives can contribute to accidents. Therefore, driveway widths and spacing should be regulated as discussed in Chapter One of this manual. All access to parking stalls in large developments should be from interior roadways or aisles. The parking spaces for any offstreet area should be laid out so that direct access to any parking stall is at least 40 feet, and preferably 60 feet, beyond the curb line of any abutting arterial street. Drive-in facilities such as banks and car washes characteristically have sharp peaks in their daily activities when customer demands exceed servicing capacity, so ample reservoir space (temporary standing areas for the driver occupied vehicle) should be supplied. The recommended minimum number of reservoir spaces for the three most common drive- in operations are: Bank (drive-in) 10 spaces Car Wash 20 spaces Theater (drive-in) 10% of capacity Without adequate reservoir space, vehicles will stand in the street and traffic congestion and accidents can be expected. TRAFFIC CONTROL PROGRAM REVIEW An important aspect in the effective use of traffic control measures such as one-way streets, traffic signals, stop signs, speed zones and parking restrictions is that they be developed on a coordinated basis. This coordination includes the consideration of the interaction and impact of proposed measure with existing controls or others under consideration. Consideration should also be given to the interrelationship between the probable effects of controls on traffic flow and the anticipated growths and changes in flow that scheduled or proposed major street improvements will bring about. Therefore, it is important to prepare and update a traffic operations improvement plan annually as one of the elements of the community's traffic improvement plan. The traffic operations improvement plan should cover items such a: 1. New and revised traffic signal installations 2. Traffic signal system control 3. Curb parking prohibitions and time limit controls 4. Turn prohibitions 27 5. One-way streets 6. Stop and yield signs The plan should include an indication of the priority of the various proposed operational measures in terms of when they will or should be scheduled for implementation. With that information available for proposed traffic operations improvements, implementation can be coordinated with other traffic and transportation improvements annually in the urban areas transportation planning program. A defined traffic operations improvement plan can also serve as the basis for evaluating traffic control requests initiated by other public agencies, citizen groups, and individuals. No plan can be expected to cover every traffic control proposal or.need that develops in a city. Therefore, provisions must be made for additions or deletions from a proposed operations improvement pro- gram if engineering studies show that the change is needed. However, prior to any modifications of the approved traffic operations improvement plan, the following questions should be considered: 1. If the proposal requires or calls for the installation of a traffic control device, does the proposed installation meet the warrants and standards of the current edition of the Manual of Uniform Traffic Control Devices? 2/ 2. Is the proposal intended to improve the safety and efficiency of traffic movement? Generally this question cannot be answered unless the proposal is evaluated in a detailed engineering study. Improper use of traffic control measures can reduce the efficiency and safety of traffic flow rather than improve it. 3. Will the proposed traffic control measure essentially be self enforcing? No traffic measure can be enforced at all times. However a control measure that is developed on the basis of accurate and adequate facts and applied according to recognized standards and guidelines can be expected to be obeyed with a minimum of enforcement. Conversely a control measure that is arbitrarily initiated can be effective only when drivers believe it is actually being enforced. If the answers to the questions above are negative, the proposed control measure should not be recommended for implementation. It can be assumed that the situation or problem which prompted the proposal either is not of the magnitude it is reported to be or that there is a better solution than the one proposed. TRAFFIC CONTROL DEVICE INSTALLATION AND MAINTENANCE A program to improve traffic operations through the use of traffic control measures cannot be expected to have continuing or even initial effectiveness unless the devices that are used are installed and maintained properly. 28 Standards for traffic control de-vice installation and performance levels for their maintenance have been developed on the basis of experience in a wide range of city sizes. The basic guidelines for an adequate program are: 1. Installation of all devices -- traffic signs, signals and pavement markings should be installed in conformance with the standards and requirements of the Manual on Uniform Traffic Control Devices. 2/ These standards cover the - location (height, position in the roadway, etc.), the physical aspects (size, shape, color, etc.), and the use of the control device. 2. Traffic sign maintenance - all signs should be inspected at least once every six months. This inspection should cover the physical condition of the sign face including its reflectivity at night under automobile headlights, position of the sign, the security of the mounting and support hardware, and the signs visibility as affected by tree and shrub growth and other obstructions. The inspection procedure should be set up to identify any location where an officially authorized sign is missing. 3. Pavement marking maintenance -- the service life of pavement markings should be determined for local conditions and marking replacement work should be scheduled accordingly. 4.. Traffic signals a. Routine maintenance -- every traffic signal should be checked and serviced, if necessary,at least once every three months. The check should be made by a competent signal repairman. In addition to the routine preventive maintenance procedures prescribed by the equipment manufacturer, checks should be made to determine if the timing controls and related operational features are functioning correctly. b. Emergency repair -- there should be a qualified signal repairman available on a 24-hour basis for emergency signal repair. c. Bulb replacement should be made on a schedule based on expected service life, not after bulbs burn out in service. d. The day and night visibility of every traffic signal installation should be checked periodically. 29 The non-professional manpower requirements to carry out a basic minimum traffic control device installation and maintenance program meeting the above guidelines will depend on factors such as city size, density of development, and whether or not work is done by contract. As a "rule of thumb," however, an average city of 15,000 to 75,000 population should have a minimum of 1.5 technicians with basic skills in traffic control device maintenance and installation per 10,000 population, This minimum manpower requirement does not provide for the installation of new devices by city forces. TRAFFIC ENGINEERING RECORDS AND DATA COLLECTION A complete system of traffic records supported by an adequate data collection program is essential for a continuing program to improve street system operations through the use of traffic control measures. These records can be grouped into three categories: 1. Records of traffic and traffic related events 2. Records of traffic regulations and control measures 3. Records of traffic control installation and maintenance work Accident Records Information on the traffic accidents that have occurred in the city are a basic record in the first category. In most cities, the collection and record keeping for accidents is a police responsibility. Therefore administrative procedures should be established to provide the agency responsible for traffic operations six basic items of information on all reported accidents in the city. They are: time, date, location, severity (fatal, injury, or property damage only), type of accident (pedestrian, fixed object, right angle, rear end, etc.), and the file reference number for the complete report on the accident. With those six items, a traffic operations agency can establish an accident location card file adequate for their routine.needs. These files generally are set up with a card for each intersection and mid-block street location where an accident has occurred. A typical card is shown in Figure 4. It provides columns for each of the six items previously identified and space for remarks if appropriate. Tabs or other identifiers may be used to mark cards or locations when the number of accidents in a given time period exceeds a pre-determined number (often 5 in 12 months). This provides an easy identification of locations that require a detailed study. This type of a card file can serve as the basic operations accident record system in jurisdictions with less than 1,500 accidents per year. An accident spot map can serve as a use- ful quick reference supplement for the card location file. In States with centralized data processing of all accident reports, a city may be able to minimize local record keeping efforts and use the centralized record bureau. For effective use of state records, the central data processing unit would have to furnish the local jurisdiction a list of all area accidents by location and description at least once a month. In addition, the local agency would have to receive periodic tabulations of high accident locations. Even with 30 Click HERE for graphic. Figure 4 TYPICAL ACCIDENT LOCATION CARD 31 a complete information flow from a centralized State agency on accident records, an accident spot map could still provide a useful quick reference to supplement the computer tabulations, Volume and Other Traffic Records Volume information is the second important traffic record that a city should have readily available. The volume record system should have traffic volume data for enough locations in the city to permit a quick and easy determination of the volume for any point on the arterial and collector street systems. At a minimum, this system usually will require volume information for all signal controlled intersections. These volume counts should cover the period from the start of the morning peak traffic period to the end of the evening peak-hour. The information should be updated every two years. A traffic count program using either manual or portable mechanical counters can be set up to provide this information.' In addition, in many jurisdictions the State highway agencies have traffic counts at key locations in the city and this information should be incorporated into the city record system. Records of other traffic characteristics such as traveltime on major streets, curb parking space use, and parking duration and space use in offstreet parking areas, can provide useful information in the analysis of a city's traffic problems. However, these data can be collected on short notice if required, and are not essential for a basic traffic operations records system. The system should be designed to maintain these records if and when the data are collected. The Manual of Traffic Engineering Studies 1/ is a reference that can be used for information on organizing and conducting the studies necessary to collect the traffic data for the record system described above. Traffic Regulation Records A readily accessible record system on the location of traffic regulations and controls is essential for the efficient operation of a city's street system. These record systems should cover locations of: one-way streets, through streets, isolated stop signs and yield signs, traffic signals, and major parking restrictions. This location information can be conveniently displayed on large scale maps. Usually one map can be used for two or three types of regulations. Traffic Control Device Installation and Maintenance Record Records covering traffic control device maintenance and installation are an important supplement to the regulation and control inventories, and they are an essential management tool for the efficient operation of a city street system. This record system is usually broken down into three major components: traffic signs, traffic signals, and pavement markings. The record tan be in the form of a multiple entry job work order such as the one illustrated in Figure 5. 32 Click HERE for graphic. Figure 5 SAMPLE WORK ORDER for TRAFFIC CONTROL DEVICE MAINTENANCE AND INSTALLATION 33 The basic information to be included on the work order is; 1. Type of device 2. Location 3. Legal or administration authorization for the initial installation Subsequent entries should be made on the same form or appended to the form each time the device is inspected, repaired or replaced. These entries should give the date, employee identification, and a description of any work done. Sign and pavement-marking work orders also should include a dimensioned non-scaled drawing showing the location of the sign or pavement markings. The record system for traffic signals, in addition to the basic information, should include current "as built" or "as modified" plans and a record of the initial signal timing and subsequent changes. Separate files, on a location basis, should be kept for the work orders on signs, signals, and pavement markings. In addition, a cross-referenced file by sign type will facilitate sign maintenance programming, material purchasing and budget planning. These work orders on control devices should be accurate and complete. Cities increasingly are involved in damage suits in which it is alleged that a traffic control device was inadequate, missing, or improperly installed or maintained. A proper maintenance program backed by adequate records can be an important item in a city's defense in such suits. 34 REFERENCES 1. Institute of Transportation Engineers, Manual of Traffic Engineering Studies, (Arlington, VA, 1976). 2. United States Department of Transportation, Federal Highway Administration, Manual on Uniform Traffic Control Devices, (Washington, D.C., U.S. Government Printing Office, 1978). 3. Levinson, Herbert S. and Hoey, William F., "Optimizing Bus on Urban Highways," Transportation Engineering Journal, (New York, American Society of Civil Engineers, 1974 4. American Public Works Association, A Survey of Urban Arterial Design Standards, (Chicago, Il. 1969.) 5. Transportation Research Board, Parking Principles, (Washington, D.C., National Academy of Sciences, 1971). 6. Transportation Research Board, Highway Capacity Manual, (Washington, D.C., National Academy of Sciences, 1965). 7. Highway Users Federation, Traffic Control and Roadway Elements, Their Relationship to Highway Safety, Washington, D.C., 1968-1971). B. Baker, Robert F., ed, Handbook of Highway Engineering, Sec. 6, (New York, Van Nostrand Rheinhold Company, 1975). 9. Jones, David W., Nakamoto, Takuya, and Cilliers, Matthys P., Flexible Work Hours: Implications for Travel Behavior and Transport Investment Policy, (Berkeley, of California, (1977). 10. Highway Users Federation, Engineering For Traffic In A Small City, (Washington, D.C. 1970). 19 825 * U.S. GOVERNMENT PRINTING OFFICE 1980 0-320-196/6270 35
