Automatic vehicle location

Introduction

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 the norm for fixed-route systems. AVL is very common on bus rapid transit systems.

Culver City's CityBus uses Automatic Vehicle Location on its buses. Photo by Flickr user DPRegionalTransport.

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 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 measure a 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. Dead-reckoning sensors can use 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 with one.

Expected Benefits

Many operators have found that AVL has helped to improve service by increasing schedule adherence and reduce response time to operational problems by improving communication between bus drivers and dispatchers. AVL also can help agencies monitor bus driver performance. Dispatchers can handle communication and monitoring a greater volume of vehicles. Passengers also perceive their transit systems as more modern and reliable because they can access real-time bus arrival information. AVL also aids in planning by collecting better historical data.

Challenges

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 also reported that after they implemented AVL, they had much greater information technology needs and had to hire staff specifically for IT.

Additional Reading

Transit Cooperative Research Project. “TCRP Synthesis 73: AVL Systems for Bus Transit: Update.” 2008.

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.

Transit Cooperative Research Program. “TCRP Synthesis 24: AVL Systems for Bus Transit.” 1997.

This synthesis, sponsored by the Federal Transit Administration, describes the challenges of developing and deploying automated vehicle location (AVL) systems. This report describes state of the practice at the time of its publication and the 2008 update examines how the industry and practice has changed since 1997.