How Automatic Vehicle Location (AVL) Systems Work

A Detroit Department of Transportation route information sign at the Rosa Parks Transit Center. The sign tells you when the next bus will come for a particular route. Christopher MacKechnie

How Automatic Vehicle Location (AVL) Systems Work and How They Are Used in the Transit Industry

AVL, automatic vehicle location, systems are widely used in the transit industry as a way to track where vehicles are in the field. In conjunction with automated passenger counters (APCs) , AVL devices make up the two most important technological advances in the transit industry over the past twenty years.

How Does AVL Work

In a nut shell, AVL systems feature two major parts: GPS systems on board each bus that track the real-time location of the bus, and software that displays the location of the buses on a map. Usually the GPS system is first beamed up to a satellite and then down to the end user. AVL is usually accurate to within thirty feet of a bus's location, which is adequate for transit but may not be precise enough for other applications of GPS tracking, including military applications. Modern GPS-based AVL is an outgrowth of an industry that had its start by monitoring the location of trains through the use of transponders strategically placed along the track.

Uses of AVL

Before AVL systems became implemented, transit supervision had no idea where each individual bus and driver were located unless the driver called them on the phone to report. Now in systems that are AVL equipped supervisors can easily see where all the buses are in their office, which helps them respond better to unplanned service disruptions as well as monitor headway adherence and on-time performance.

AVL has allowed road supervisors to focus more on incidents such as accidents and criminal activity and less on routine bus monitoring.

Some transit systems use AVL to automatically produce internal and external stop announcements, which are required under the federal Americans With Disabilities Act .

Transit systems can also use AVL to automatically display the correct destination sign, but this usage can prove problematic if the AVL system malfunctions, which happens more than AVL providers might like.

In addition to internal use, transit systems are more and more displaying their vehicle locations to the general public through the use of internet-based live bus tracking, telephone-based next bus information, and on-street signs that show estimated real-time arrivals of the next few buses. Long Beach Transit in California has been an industry leader in this area for years. They have shown live bus locations on the internet for many years, have added on-street signs showing the expected arrival time of the next for buses for the last couple of years, and have recently added a telephone system where callers can learn the expected arrival times of the next few buses that are going by a stop location that they input. Los Angeles Metro shows the real-time location of the bus on board by using a TV screen that also shows news, weather, and of course advertising, and has recently entered into beta-testing of a phone system similar to Long Beach Transit.

Cost of AVL and Prevalence

TCRP Synthesis 73 in 2008 reported that for fleet sizes less than 750 vehicles the cost was $17,577(Fleet Size) + $2,506,759.

 Other figures suggest a range of $1,000 - $10,000 per bus, with an added maintenance cost of $1,000 per bus. This cost, which is not unsubstantial, probably explains why a United States Department of Transportation study in 2010 found that only 54 percent of fixed-route transit systems in the United States use AVL.  The cost, which likely continues to decrease, was clearly supported by a study that found a Benefit/Cost ratio for AVL systems of between 2.6 and 25.

Outlook for AVL

AVL, more so than APC, is a critical technology for today's transit system. While bus drivers such as myself may wax nostalgic for a time when our supervisors did not know where we were at all times, it is extremely valuable for a transit system to know where its vehicles are at all times. It can even prove to be critical in the case of accident or crime where every second assistance is delayed increases the chance of injury or death.