Introducción al AVL

Automatic Vehicle Location Printer-friendly version
What Is It?
Automatic vehicle location (AVL) is a computer-based vehicle tracking system. For transit, the actual real-time position of each vehicle is determined and relayed to a control center. Actual position determination and relay techniques vary, depending on the needs of the transit system and the technologies employed.
Transit agencies often incorporate other advanced system features in conjunction with AVL system implementation. Simple AVL systems include: computer-aided dispatch software, mobile data terminals, emergency alarms, digital communications. More sophisticated AVL Systems may integrate: real-time passenger information, automatic passenger counters, automated fare payment systems, automatic stop annunciation, automated destination signs, vehicle component monitoring and traffic signal priority. See our Telecommunications Diagrams of GPS-based AVL and Signpost-based AVL for more information.
Key Results
Starting in the early nineties, there has been a significant shift from odometer and signpost systems to Global Positioning System technologies. The dominant AVL technology deployed today is GPS, representing close to 75% of all systems deployed. Research (Gillen et al., 2000) indicates that there is currently no clearly superior technology (in terms of transit firm productivity) therefore the relative cost of comparable AVL systems should be the main consideration in selecting a system. However, GPS may become a more cost-attractive option in the near future as the U.S. Government stopped the intentional degradation of GPS signals available to the public starting May 1, 2000.
Recent evidence indicates that AVL technology is leading to significant transit firm productivity gains as well as increases in transit ridership. AVL technology allows: improved schedule adherence and timed transfers, more accessible passenger information, increased availability of data for transit management and planning, and efficiency/productivity improvements in transit services.
AVL also creates many possibilities for ITS systems integration including: providing transit buses with traffic signal priority; incorporating transit information in traveler information systems; developing multi-application electronic payment systems and using buses to automatically communicate traffic speed.
The most extensive and rigorous research into the benefits of AVL (Gillen et al. 2000) has found that this technology has lead to significant transit firm productivity gains (whether output is measured by Passenger Miles or Vehicle Revenue Miles). Benefits have been documented to varying degrees for all of the following categories:
Transit firm productivity gains: increased passenger trips, capital savings (potential reductions in fleet size due to better utilization of vehicles), lower annual maintenance costs and generally a lower vehicle cost per mile.
Improved schedule adherence, accuracy in schedule adherence monitoring and transfer coordination.
Increased transit ridership.
Labor savings: reduced need for additional road supervisors and manual data entry.
Improved ability of dispatchers to control bus operations as well as better monitoring of driver performance.
Effective tracking of off-route buses as well as paratransit vehicles and drivers.
Improved communications between supervisors, dispatchers, and operators.
Reduced voice radio traffic.
Passenger Information:
Provides capability to inform passengers of predicted bus arrival times thus enhancing the quality of transit service and allowing travelers to make better travel decisions.
Reduces schedule adherence customer complaints and the need to add customer information operators.
Scheduling and Planning:
Provides more complete and accurate data for scheduling and planning.
Potential reduction in schedule preparation time and staff.
Aids in effective but stop placement (when combined with a G.I.S. database and automatic passenger counters).
Safety and Security:
Enhances driver and traveler security (particularly when coupled with silent alarm technology) by allowing quick location of vehicles and faster security response.
Enhances driver and traveler safety: accurate and quick location information allows for faster response to accidents.
Better operational response during detours caused by accidents, roadway closings or bad weather.
Procurement costs to install the equipment and the software both on-board buses and at the operations/dispatch center.
Labor: maintenance of on-board AVL equipment and operations center equipment, time required to learn new systems and new technical staff at the operations center.
The costs of AVL installation are dependent on the size of the system, its level of sophistication, and the components to be included. Systems can range from those with fairly basic features to very comprehensive systems. There is a significant cost for the equipment and software that reside at the operations/dispatch center. The per-bus cost of large fleets is less than for smaller fleets, assuming similar features, because the cost of this major infrastructure is distributed over a larger number of vehicles. Taking these factors into consideration the cost per AVL-equipped bus can range from $6,800 to $30,500, with an average cost of $15,500 per bus (FTA, ITS JPO August 2000, based on a survey of 6 transit agencies of varying size).
Implementation and Operational Challenges
Early adopters of AVL systems experienced many technical and institutional problems. The biggest challenge for agencies implementing AVL today is the potentially lengthy procurement and installation period (particulalry software development and integration of technical components). For this reason, agencies purchasing an AVL system may want to use an existing design, with customization capabilities. Other implementation and operational challenges to consider are:
Institutional relationships may be difficult.
Development of new software or extensive customization of existing software can result in many possible problems.
Considerable effort may be required to establish an accurate geographic information system database.
Systems should be consistent with the National ITS Architecture.
New technical expertise is usually required at the transit agency.
Some existing staff may be reluctant to learn the new technology.
The schedule adherence function design requires careful thought.
A global positioning system signal reception problem may occur in certain areas.
Where is it Implemented?
Simple AVL systems are implemented throughout the United States, Western Europe and in South East Asia.
Comprehensive AVL systems are being implemented in those regions on a limited basis. However, comprehensive AVL systems are being increasingly deployed.
Author: Dimitri Loukakos

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