André Ampélas

Michel Daguerregaray

RATP - Regie Autonome des Transports Parisiens

Better informed passengers, improved bus interval management, and increased security -that's what RATP (Regie- Autonome des Transports Parisiens, the city's public transportation provider) sought when it considered implementing a GPS-based vehicle location system. With 4,000 buses operating in the greater Paris, France, region, such an undertaking is no small feat. The project has spanned almost nine years, from concept to full deployment, with completion expected next year.

In 1991, RATP managers began investigating the possibility of using GPS tracking technologies to improve operations. We knew that, like any business, the key to a successful public transportation system is maintaining profitability as well as customer and employee satisfaction. For RATP, that meant addressing three major concerns: security, information distribution, and route management.

Safety is critical if people are to choose public transportation over other options and if a company wants to maintain a staff of quality drivers. Traditionally, in the event of an incident, a driver radios the dispatch office to communicate the vehicle's position and request help. If, for whatever reason, the driver can't provide this information, the dispatcher must estimate the bus's location and send emergency crews to look for the stopped vehicle. We knew that such a slow and inefficient system needed to be changed, particularly given Paris' ever-growing popularity and the consequent increase in bus usage.

We also knew that passengers waiting at RATP stops wanted more information about bus arrival times and didn't want to wait longer than the scheduled time, only to then see two or even three buses arrive in succession. We therefore began our search for a way to better control the RATP fleet, preferably with a system that would solve all three problems at once.

After carefully considering our options we had already conducted experiments using infrared beacons and terrestrial high frequency radio positioning - we decided to put GPS to the test. Initial research indicated that GPS's potential strongly matched our requirements, so we proceeded into the project's next phase - a prototype period.

EQUIPMENT ESSENTIALS

Before placing any GPS receivers on a bus or investing in any type of equipment, we evaluated the available hardware and software in terms of our application's requirements. These included compatibility with existing in-vehicle systems, easy user interfaces for both passengers and drivers, and the ability to cope with the innercity phenomenon known as the urban canyon. The latter issue implied the need for fast reacquisition times at crossroads and a resistance to multipath, caused by reflections from buildings.

In 1994, after. concluding the prototype period, RATP began an experimental application of its GPS-based surface vehicle radio-location system. In this phase of the project, we aimed to demonstrate the viability of satellite-based vehicle positioning in urban zones and under actual working conditions. We placed the equipment on 60 buses and 20 security cars to test it under real operating conditions.

Communication. Once we had proven GPS's capabilities, we quickly moved toward implementing the system a on actual routes. Although the buses already had radios for voice communications, those transceivers were not designed for sending data. We therefore implemented a 3RD radio communications network developed for data transmission using the Mobitex protocol.

Initially, we used France Telecom Mobile Data services for our data transmissions. Since the end of 1996, though, we have employed our own 3RD network that covers the better part of the Paris-Ile de France region. This arrangement allows us to offer our communications services to police vehicles and other users. We have data interfaces, for example, with the police department's information system.

Onboard Equipment. In addition to the radio transceiver, we must install a GPS receiver on each bus. We selected an eight-channel, Ll, C/A-code unit. The GPS antenna is attached to the bus's roof and connected to the in-vehicle receiver/display box. Drivers can access this unit to send messages to the control center, check on their bus's status with respect to the schedule, and obtain information about other buses on the same route.

Unfortunately, in urban areas, it is often difficult for a receiver to locate and lock onto the three GPS satellites needed to accurately calculation a bus's position. To increase accuracies, we have set up a differential base station at our central office that broadcasts correction data every 30 seconds over our private radio network. We also couple the GPS unit with a gyrometer, the bus's odometer, and an onboard calculator to enable position computations using dead-reckoning techniques. These devices, combined with map-matching software running on the system's main server, provide accuracies of about 10 meters.

Aigle and Altaïr. For those bus lines requiring only additional security, we put these positioning and data transmission capabilities into a localization package known as Aigle. All buses have the same in-vehicle devices, permitting the driver to review the route's schedule as well as the time interval between his our her bus and the next and previous bus on the same line. The upgraded Altaïr system, though, adds central server software to enable fleet control and real-time information distribution at the bus stops.

The Aigle security system, when activated, simultaneously transmits the bus's location and an emergency signal to the central security control room. This eliminates the worry about a driver being unable to supply position data as could be the case with traditional systems. In addition, in ah effort to guarantee security to its customers and its own staff, RATP decided to extend its system in association with the Paris and Ile de France police departments. Aigle client-server terminals have been installed in the police bureaus so that they, too, can have accurate information as to an incident's scene and conditions, as well as dispatch intervention forces more quickly. To further improve response time and safety, RATP also installed GPS receivers in some police cars dedicated to public transportation security.

Two versions of the Altaïr system are also available, adding the interval management and passenger information capabilities to Aigle's security features. The latter upgrade adds display units and automatic stop announcements on the buses. Without any intervention from the driver and regardless of route changes, the in-bus system announces the name of each stop as the vehicle arrives and displays the information on a scrolling LED (light-emitting diode) display. Riders can also view the bus's destination and the time to a specified, upcoming stop.

COMMAND AND CONTROL

Both Aigle and Altaïr depend on supporting infrastructure at each RATP local control room and at the Bus Traffic Control Headquarters and Security Control Room. Position data received by way of the radio network, for example, are concentrated in a central system known as the radio-location server. Its first task is to improve the positions received. It compares the data with a vectorized database that gives a detailed representation of the Paris-Ile de France region. Positions that initially appear slightly off the middle of the roads are readjusted using a technique known as map-matching. RATP teams generate the map database using Institut Géographique National (IGN) data and distribute it for use in various applications, including a passenger itinerary system.

When the map-matching; processor finishes, it sends vehicle positions to two application programs that enable the bus interval management, security, and passenger information features. The first programs, installed in the local control room of each line, allows real-time interval management of the line. Line traffic managers receive bus position updates every 30 seconds, permitting them to monitor the route in real time and to improve schedule adherence and intervals between buses.

Information Distribution. This particular software program also manages the distribution of data to the passenger information systems at bus stops. It automatically transmits the data over the radio network to the appropriate stop every 30 seconds. The passenger can thus see how long lie or she must wait (in minutes) and also the destination of die next two buses scheduled at that given stop. This allows riders to run errands, if the waiting time allows, or perhaps to choose another means of transport, if they cannot wait for the next bus.

Passengers can also obtain up-to-the-minute information about some lines using the telephone. By selecting the appropriate stop from a menu, customers receive the same information as is displayed at the bus stop.

Security Software. The second program is installed at the Maison de la RATP, the central office, in the Bus Traffic Control Headquarters and Security Control Room. This software enables the Aigle's security functions. In the event of a driver emergency c 1 the bus's position is displayed on a map updated every 10 seconds. Eighty emergency vehicles - including RATP units and police cars - are equipped with GPS and also displayed on the security room's map. This saves time when searching for and alerting the vehicle nearest to the bus in difficulty. RATP dispatchers also have a radiotelephone link with the emergency stations to communicate a bus's position.

DEPLOYMENT DETAILS

In 1994, RATP moved into the experimental application phase, completing it in October, This involved deploying Aigle on 40 buses and Altaïr on 20 buses. By April 1995, the entire system was fully operational, with all control and security rooms as well as the buses functioning and communicating as planned.

As of June 1998, we had installed the GPS-based radiolocation system on 300 vehicles, including the 80 emergency intervention units. Suburban line 256 was outfitted for security purposes only (Aigle). Lines 47, 62, 272, and the train line N'2 (T2) have the complete Altaïr system, with passenger information and bus interval management, as well as Aigle. And line 262 and the night buses (Noctambus) operate with a simplified Altaïr system offering Aigle and bus interval management only.

In addition, we equipped Line 62 in April 1997. This line, the longest in Paris after the Petite Ceinture (ring road bus), runs from Porte de Saint Cloud to Cours de Vincennes. It travels through narrow shopping streets, which bas allowed us to fine tune the system for optimal performance in the urban canyon. Just after that line became operational, riders from Montparnasse to Porte de Champerret received the same capabilities. Finally, in the second half of 1997, line 272 was equipped with a full system to replace the simple security system it had previously

Half Way There. Our initial deployment phase will see half of the network equipped, with the first lines outfitted chosen mainly on the criteria of security and irregularity of passages. Those 2,000 vehicles will be equipped with the security system by the end of 1999, Routes receiving the additional features the passenger information and interval management systems -will be operational in mid 2000. Altaïr should then be installed on all other lines by mid 2000, thereby fulfilling RATP's ambition to step up security and service quality in the bus network.

SUCCESS AND THE FUTURE

RATP's initial objectives, interestingly enough, have already been attained. To confirm that we are in fact providing the level of service we envisioned, we have made measurements to check the accuracy of the passenger information, during both peak hours and less burdened times. The results have indicated that our data were accurate to 30 seconds for waiting times as long as 4 minutes and to within less than a minute for waiting times of 10 minutes.

The reliability of that information has made the bus a more-dependable means of transport in the eyes of the passenger. The interval management feature bas also allowed managers and bus drivers to adjust schedules as necessary to eliminate, strings of buses and respect regular intervals at the stops.

In addition, plans are already in the works to further improve security by enabling correct diagnosis of the situation. Line 272 is testing an upgraded Aigle system that transmits sound and video images obtained inside the bus when the emergency signal is sent by the driver, The camera sends pictures from before and after the signal at a rate of one picture every 5 seconds. The pictures are digitized and compressed on board during filming and decompressed at the security center to save time. The first series of images is highly compressed to give operators an immediate overall view of the situation (seriousness, number of aggressors, and so forth). Dispatchers can then request more accurate pictures to analyze detail, as they can control the camera imaging rate and compression factors.

Financially Speaking. Although the many functional improvements made possible through GPS and other localization technologies are impressive and have made improved service at RATP possible, the main revolution brought about by the Altaïr and Aigle systems has been economic - a critical factor for public transport, which is often subject to financial difficulties. The overall price of the Altaïr application bas already been reduced threefold compared to the previously used, traditional wire-supported systems, which has rendered its generalization to the entire network economically viable. The launching of large production lines will also increase price cutting, as will the sharing of the radiolocation server, which other fleets such as maintenance or urban vehicles are starting to use.

And finally, this new technology, which allows considerably better service quality for a marginal cost Qess than 0.5 percent of the transport's overall cost), will open up new avenues for both publie transport and other urban applications, including such capabilities as interconnection with traffic light systems and swift vehicle scheduling before a line is implemented. RATP is entering a new era in public transportation, with the future promising further innovation and more improvements that will ensure its place on Paris's streets as the preferred form of transport for millions.

Source : GPS World October 1999