APMS—What Are the Technology Options?
"Uniquely uncommon causes [for power and communications obstacles] are not always considered or investigated during the design engineering phases prior to such demonstrations or deployments."
–Barry Resnick, Planner, Department of Planning and Real Estate Development, Metra
When planning advanced parking management systems, two main decisions need to be considered: "What type of system will count the number of vehicles in the facility?" and "How will the various components of the system communicate with each other?"
Counting Systems
There are two types of counting systems: entry/exit counters and space occupancy detectors.
Entry/Exit Counters
Entry/exit counters can use one of several technologies currently available. Traditional induction loop counters can be employed where surfaces and anticipated weather treatments support their application. In cases where loop detectors are not feasible, video detection technologies similar to those used in actuated traffic signal control may be considered. Another alternative, shown in Figure 5, is the use of small ultrasonic counting devices installed in the surface of the roadway. These devices can be powered by long-life batteries and can communicate using a radio frequency (RF) transmitter.
Figure 5. Entry/Exit Counter (Highlighted in Pavement) with Traffic Delineation Guide
Space Occupancy Detectors
Space occupancy detectors are manufactured for installation in the ground under the vehicle, on a post in front of the space, or over the space on garage ceilings. Most occupancy detectors use ultrasonic sensors or induction loops. Each approach has unique power and communication requirements.
Communication Systems
Traditionally, APMS applications have focused on solutions that employ closed systems that use dedicated resources to generate and display parking space availability in real-time. These closed systems—such as Chicago Metra and BWI Airport—use signs, space occupancy detectors, and a dedicated central computer. These systems typically use dedicated fiber optic lines to communicate between nodes. Though these systems provide real-time, high-quality information, they are expensive and usually require that the communications infrastructure be included in the facility construction. These systems may also require purchase or lease of dedicated fiber optic communications capacity to serve the APMS sign system.
Because not all APMS projects involve new construction, fiber optic communications are not always practical. Space occupancy sensors that use RF communications are a good choice when existing facilities are retrofitted with an advanced parking management system. These RF transmitters communicate between individual parking spaces and a local hub. The local hubs collect and forward that information using wireline or wireless media to the central computer.
Communications with APMS signs can also be accomplished wirelessly using owned or leased microwave systems that operate under Federal Communications Commission (FCC) guidelines. Cellular telephones are generally not practical as a communications medium, due to the frequent communication required to update the information that is necessary to maintain an accurate count of available spaces.
Factors to Consider When Choosing Counting and Communication Systems
When choosing a technology option, decision-makers need to consider whether the facility is new construction or a retrofit, whether the facility is subject to periodic repaving, and whether or not the parking configuration will change over the long term. Whether new construction or a retrofit, stakeholders should expect some challenges in dealing with dynamic field conditions.
Barry Resnick, Planner for the Department of Planning and Real Estate Development at Metra, said, "Uniquely uncommon causes [for power and communications obstacles] are not always considered or investigated during the design engineering phases prior to such demonstrations or deployments." Metra was proactive in addressing any potential issues by calling for a radio frequency field study as part of the construction bid.
Each ITS-based parking management solution is different, requiring a carefully chosen architecture that meets the needs of the various stakeholders. Factors that should be considered when deciding among these options include:
- Availability of mounting space for detectors
- Operational environment in which the components will be used
- Communication channels
- Electrical power supplies.