Transit Technologies                                                              Printer-friendly version

• Introduction
• Automatic Vehicle Location
  • AVL Technologies
• Electronic Fare Payment
• Traveler Information
  • Types of Traveler Information
• Transit Security
• Traffic Signal Priority
• Precision Docking at Bus Stops
• Computer-aided Dispatch
• "Smart Buses" Case Studies

Introduction

ITS applications to transit include Automatic Vehicle Location, Electronic Fare Payment, Traveler Information, Transit Security, Traffic Signal Priority, Precision Docking, and Computer-Aided Dispatch. While in-depth reports on most of these technologies are available elsewhere on ITS Decision (see links to these reports in each section below), summaries of their main features are provided here.

Automatic Vehicle Location

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. Typically, vehicle position information is stored on the vehicle for a time, which can be as short as a few seconds or as long as several minutes. Position information can be relayed to the control center in raw form or processed onboard the vehicle before its transmission. See our Telecommunications Diagrams of GPS-based AVL and Signpost-based AVL for more information.

Transit agencies often incorporate other advanced features in conjunction with AVL implementation. AVL systems normally include the following components:

• Computer-aided dispatch software
• Mobile data terminals
• Emergency alarms
• Digital communications

AVL Technologies

AVL systems use one of four types of navigation technology, or may combine two of these technologies to compensate for inevitable shortcomings of any one technology. The four principal technologies employed for AVL systems are:

• Global Positioning System (GPS Satellite Location)
• Signpost and odometer
• Radio navigation/location
• Dead-reckoning

Global Positioning System
GPS is the newest of these and is by far the most popular choice for transit agencies implementing new AVL systems today. GPS employs the signals transmitted from a network of satellites orbiting the earth. These signals are picked up by a receiver onboard the bus. The satellite system covers almost all of North America, eliminating the need to place transmitters/receivers along any route. The existence of the satellite system means that the main cost for the agencies result from purchase of the GPS receivers and equipment to transmit to dispatch. The accuracy and reasonable cost of GPS make it the most appealing option, though it too has some problems. Foliage, tall buildings, and tunnels can block the satellite signal, and at times satellite signals do not reach specific locations. Some agencies use dead reckoning in conjunction with GPS to fill in such gaps.

Link to story on how GPS works: http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=102387

Satellite Technology in Europe
Until recently, Europe has depended on information derived from GPS satellites and from the Russian GLONAS satellite systems, combing satellite technology other, older systems. Without a true alternative to GPS, however, certain areas of Europe, particularly in northern Europe, were not well covered by satellite technology. However, major changes are underway in Europe. A system called EGNOS began a test phase in early 2005. This system comprises a network of more than 40 European ground stations that record, correct and improve data coming from the US global positioning system (GPS). The modified signals are communicated to users via geostationary satellites. More significantly, Europe is developing its own satellite technology, known as Global Navigation Satellite System (GNSS), or Galileo. Galileo is based on 30 satellite constellations supported by ground stations. Galileo, which will be under civilian control, is expected to begin operating in 2008. With the addition of these 30 satellites, positions will be determined far more accurately for most places on Earth, even in cities where buildings obscure signals from satellites low on the horizon.

Link to story on satellite technology in Europe
http://europa.eu.int/comm/dgs/energy_transport/galileo/intro/index_en.htm

Dead-Reckoning
Some transit agencies use dead reckoning systems in combination with GPS. Dead reckoning systems, among the oldest navigation technologies, determine vehicle position by measuring distance traveled from a known location and direction of travel. Dead reckoning sensors can measure distance and direction from a fixed point (under the most basic setup, an odometer and compass could be used to calculate position from a specific stop on a route). Typically, these systems act as a backup to another AVL system. This relatively inexpensive system is self-contained on the bus. Dead reckoning, however, has a number of drawbacks. Uneven surfaces and hills can compromise the positioning information. Should the vehicle leave a fixed route, its location will no longer be known since there will be no waypoints off the fixed route. Also, accuracy degrades with distance traveled, and regular recalibration is required (tire circumference changes with wear).

Signpost/Odometer Systems
The signpost/odometer system was the most common navigation technology until the advent of GPS. In this system, a receiver is mounted on the bus, whiletransmitters are placed along the bus’ route. Utility poles and signposts are most commonly used as mounting locations for these transmitters. The bus picks up a low-powered signal from these transmitters as it passes by and the mileage is noted. When the bus reports its location, the distance from the last pole is used to locate the vehicle's position on a route. The system can be run in reverse, with the transmitter on the bus and multiple receivers mounted along the route. However, should the bus need to leave the route, there will be no information about the bus, so most agencies prefer to have a receiver on the bus. This older technology has some drawbacks. Creation of new routes requires the placement of new transmitters, and the system is maintenance intensive due to the relatively high number of transmitters and receivers involved.

Radio Navigation/Location
Radio navigation systems also tend to be combined with other systems. Radio location systems use a low-frequency signal to cover the system, and the buses are located as they receive the signal. Loran-C (Long Range Aid to Navigation) is the most common type of land-based radio location. Despite the simplicity of the system, it is subject to some major drawbacks. Overhead power lines or power substations can cause signal interference, and signal reception is typically very poor in canyons.

Click here for a detailed report on AVL.

Electronic Fare Payment

Click here for the ITS Decision report on Electronic Fare Payment

Traveler Information

Some bus routes provide real-time bus arrival information at bus stops (frequently referred to as "next bus" signs). These signs use an automatic vehicle location (AVL) system; in this system, a GPS unit onboard the bus communicates its ID# and location information to an information center. Taking into account the actual position of the bus, its intended stop, and the typical traffic patterns of its route, this center estimates arrival information and sends this info to an electronic display at the bus stop. Next bus signs can be found in the San Francisco MUNI system at major stations along the entire J, K, L, M, and N lines and along the 22 Fillmore line. They can also be found in Denver along the Vail transit route and in Rehoboth Beach, Delaware. See our GPS-based AVL Telecommunications Diagram for more information.

Typically, traveler information breaks down into two categories: static information, which is known in advance and changes infrequently, and real-time information, which changes frequently.

Static information includes:

Real-time information is what travelers have repeatedly said they value the most. Real-time information includes:

Types of Traveler Information

Traveler information can be divided into the following types of info (click on the link for more detailed information):

Enroute information - provides drivers information pertaining to traffic conditions, incidents, construction, transit schedules, weather conditions, hazardous road conditions, and recommended safe speeds while en-route. 

Enroute transit information - the information that is available to transit riders after they start their trips (includes arrival and departure times, availability of services such as park and ride, transfers within the system and connections to other modes).

Pretrip information - informs travelers of traffic and transit conditions, so they can assess travel options before selecting a route, mode, departure time, or deciding whether to make a trip.

Route guidance - technology that enables a driver to take the route that most closely matches his requirements.

Telematics - encompasses consumer products, services, and supporting systems that deliver information, communication, and entertainment to vehicles and mobile devices (e.g. personal digital assistants (PDAs), pagers, cellular phones)

Traveler services - tells travelers about attractions and travel conditions along their route.

Click here for detailed information on Traveler Information

Transit Security

The security of a transit system is part of the service that the transit agency provides. Passengers regard their safety as the agency's responsibility. Crimes committed in transit systems include disorderly conduct, public drunkenness, non-payment of fares, theft, harassment/threat, narcotics, weapons violation, purse snatching, simple assaults and batteries, robberies and attempts, aggravated assaults, sexual assaults, rapes and attempts, and homicides and attempts (Needle, 1997). These crimes occur in transit stations, at transit stops, or on board transit vehicles, and often at night.

Most safety and security improvement measures can be categorized as one of the following types: patrol and security, design actions, media and information campaigns, technological innovation, transit service improvements, and increasing sanctions of offenders (Ingalls 1994, Wallace 1999). New technology, such as monitors and automatic alarms, can improve transit system security. The main technologies used are:

• CCTVs
• Call boxes/emergency phones
• Alarms
• Automated ticketing and fare systems.
• Automatic Vehicle Locations Systems (AVL)
• Pager systems alerting travelers of the next bus arrival

Other strategies to prevent or control crime include: patrol and security, design actions, media and information campaigns, transit service improvements, and increasing sanctions of offenders.

Click here for a detailed report on Transit Security

Traffic Signal Priority

Traffic signal priority is the idea of giving special treatment to transit vehicles at signalized intersections. Since transit vehicles can hold many people, giving priority to transit can potentially increase the person throughput of an intersection. Signal priority is being more widely deployed in North America to address traffic congestion, caused by traffic signals, for on-street transit service.

There are two basic types of bus signal priority:

1. Active priority: Each bus is detected on approach to an intersection and the signals are then changed. Active systems can be a combination of real or fixed-time control strategies, and schedule or headway-based control strategies. Active concepts are more effective and widely used.
   
   
2. Passive priority: Traffic control devices are adjusted to suit the bus schedule along the route in general using a combination of fixed-time and schedule-based control strategies. In some applications, passive priority is implemented only at certain intersections – primarily it favors roads with significant transit usage, often close to the buses origin point where schedules are most likely to be adhered to – while the entire corridor has an active priority system. Passive priority does have the benefit of being lower in cost, however it has limited potential to improve bus operations.

Queue Jumpers: A queue jump lane is a short stretch of bus lane combined with traffic signal priority. This lane enables buses to by-pass waiting queues of traffic and to cut in front by getting an early green signal. A special bus-only signal may be required. The queue jump lane can be a right-turn only lane, permitting straight-through movements for buses only. A queue jump lane can also be installed between right-turn and straight-through lanes. A similar arrangement can be used to permit a bus to cross traffic lanes to make a left turn immediately after serving a curb-side stop.

Precision Docking

Precision docking refers to a variety of systems designed to enable a vehicle to align itself in exactly the same position at a station every time. Precision docking at bus stops uses sensors on buses and on the roadside to indicate the exact place where the bus should stop. Bus doors opening at the same location each time make it possible for passengers to be in position for immediate boarding once a bus has stopped, shortening dwell time. This precision can be used to achieve level, gap-free access by bringing the bus close alongside platforms. It can also allow for direct wheelchair access from a loading platform to the floor of the bus (without taking extra time). Precision docking has the following advantages:

• bus drivers will not need to make multiple attempts to park accurately
• bus drivers will not approach too close to the curb and damage the bus tires, which creates excessive maintenance costs
• cumbersome moveable ramps will not be needed

Computer-Aided Dispatch (CAD)

Computer-Aided Dispatch (CAD) software integrates transit operations by giving transit dispatchers and supervisors decision support tools to manage the operating environment. The primary CAD functions are real-time monitoring of operations and providing decision support to respond to delays and disruptions of service. Decision support recommendations include adjustment of vehicle headways, dispatching replacement or additional vehicles, or reporting incidences. Although few CAD systems have been standardized, many transit operators have noted the cost savings and efficiency gains that CAD affords.

How does CAD work?
Dispatchers are responsible for carrying out a series of actions when responding to a call from a bus operator. They usually have access to a CAD screen and an Automatic Vehicle Location (AVL) screen, which help them identify and respond to problems on their bus routes. When a bus operator calls, the dispatcher sees a message showing the bus number on the CAD screen (which prioritizes the operator calls). The dispatcher selects the vehicle calling from the incident list and refers to their Automatic Vehicle Location screen for its location. The dispatcher can enter an "incident code" that identifies the type of problem the bus is experiencing as well as call the bus operator directly. The CAD/AVL system helps dispatchers track route performance by notifying them of late or off-route buses. Dispatchers can also typically communicate with buses individually or collectively (i.e. an entire route); they can send text messages or talk via radio.

Link to list of existing CAD software used for public safety

Smart Buses Case Studies

Long Beach TranSmart
Long Beach Transit is in the process of implementing TranSmart, a satellite-controlled, computerized system for tracking its bus fleets. Buses are equipped with GPS so that the dispatch stations can track their location, which allows transit supervisors to alert passengers of where the bus is and when it will arrive (to the minute). Passengers receive real-time bus location information on electronic TranSmart signs placed at select stops. Voice announcements will be tied to the GPS system to tell passengers on board and waiting at bus stops where the bus is located and what stop is coming up. Buses will also have LED displays on board to alert passengers of where they are on the route and how much time until their stop. Passengers will eventually be able to figure out where their bus is via cell phones, the Internet, or telephone.

King County Metro and the University of Washington "Mybus" program
King County Metro in Seattle has been running the Mybus program that allows passengers with Internet-ready cell phones or palm pilots to access information that will tell them whether or not their particular bus is on time or not. Metro has another Internet-based program that allows users to view bus locations within a system map on their home computers. Metro also plans to put up bus signs that provide real-time bus arrival times.

Oregon's Tri-Met Program
Tri-Met has deployed several advanced ITS technologies to improve the delivery of service on bus and rail. The computer-aided bus dispatch system (BDS) and the rail central control system (CCS) currently display the location and schedule status of all fixed-route vehicles to dispatchers and rail controllers, respectively. The Tri-Met project would allow for real-time transit information to be displayed to transit customers via communications technologies (i.e. cell phones). This project will also implement automated stop announcements on buses to assist the visually impaired.

Better buses in Raliegh, North Carolina
Buses in the Triangle will be equipped with several types of technologies aimed at improving ridership and customer satisfaction. The cameras will take footage of activities both within and outside of the bus (i.e. accidents). Stop-announcement technology will let passengers know of their location along a given route. Dispatchers can track the buses using GPS and keep traveler schedule information updated.

Houston, TX Metropolitan Transit Authority "Integrated Vehicle Operations Management System (IVOMS)
The Metropolitan Transit Authority approved funds for an Integrated Vehicle Operations Management System (IVOMS). A total of 1,350 vehicles will be equipped with next stop announcement units, mobiles radios for data radio communication and Automatic Passenger Counters. Transit Signal Priority systems will also be installed on 1,072 vehicles and used at roughly 1,250 intersections. Additionally, electronic bus stop signs will be installed and will display next bus arrival times for each route.