Automatic vehicle location
Automatic Vehicle Location (AVL) describes the use of computers and Global Positioning Systems (GPS) in dispatching and tracking transit vehicles. AVL is accompanied by added costs of operating and maintaining additional computer equipment, but transit agencies benefit from improvements to customer service through real-time information. Operating costs, however, are not generally reduced by these improvements. Because AVL is becoming so common, it is increasingly becoming expected as standard for fixed-route systems. AVL is very common on bus rapid transit systems. AVL systems can vary widely in cost - from $100 to $7,000 per bus, depending on the type of technology being used.
Types of Systems
There are two commonly used types of tracking technologies: Radio navigation and dead-reckoning technologies. Radio navigation was used in the earliest AVL systems, which use radio transponders that communicate with passing buses and a central dispatch center. These include ‘signpost’ transponders that are mounted on posts above the height of the bus, to allow communication at level with antennas on top of the vehicles. Dead-reckoning sensors on buses measure its distance from a fixed point. Some of these systems use a wheel odometer to count the number of wheel revolutions between stops as a way to measure distance. AVL systems that use dead-reckoning sensors can be made up of all on-board equipment, while radio navigation systems require communication with off-board technology. Both types of system require maintenance and calibration that can add to the costs of managing them. Some systems use a hybrid of the two technologies, using one to aid the other, or as a backup in case of problems.
Many operators have found that AVL has helped to improve service by increasing schedule adherence and enabling agencies to easily monitor bus driver performance. AVL also helps to reduce response time to operational problems by improving communication between bus drivers and dispatchers. Dispatchers can handle communication with and monitoring of a greater volume of vehicles. Passengers also perceive their transit systems to be more modern and reliable because they can access real-time bus arrival information. AVL also aids in planning by collecting better historical data. Automatic vehicle location, combined with computer aided dispatch (CAD), has also been proven to improve safety and security on transit vehicles because many systems include a silent alarm and video monitoring capabilities. Denver's Regional Transportation District saw a 20 percent drop in assaults after adding an AVL/CAD system to its vehicles.
The challenges associated with AVL are primarily found in managing expectations for the system within the agency, training staff, and ensuring that the interfaces for software and hardware work together throughout the agency, including with any paratransit service. Some agencies reported that after they implemented AVL, they had much greater information technology needs and had to hire staff specifically for IT.
- Parker, D. J. (2008). “AVL Systems for Bus Transit: Update.” Transit Cooperative Research Program.
- Schweiger, C. (2003). "Real-Time Bus Arrival Information Systems." Transportation Cooperative Research Program."
- Okunieff, P. E. (1997). “AVL Systems for Bus Transit.” Transit Cooperative Research Program.
- National Center for Transit Research at the Center for Urban Transportation Research, University of South Florida. (2005). “Enhancing the Rider Experience: The Impact of Real-Time Information On Transit Ridership.” Florida Department of Transportation.
- This update to the 1997 Synthesis, also sponsored by the Federal Transit Administration, includes detailed information about the state of the practice and how AVL has been used over the past few decades. It offers more specific information on the operational benefits of AVL and actual costs of several recent contracts awarded by transit agencies. This synthesis also provides an update of the wide variety of functions that AVL can provide, such as updated headsigns at the end of trips, that previously were not available.