GIS: London Trnasport Fine Tunes Transportation Network
Despite the prevalence of pulbic transportation, London's streets are choked with private vehicles. Now, planners are turning to GIS to help ease the congestion.
By Tony Adams and Kevin P. Corbley

Bright red, double-decker buses have become London trademarks, as closely associated with the city as Big Ben and the Beefeaters. But unlike many other well-known London sights, these buses are more than just attractions for the tourists. Every day more than two million passengers rely on the two-story buses to travel across the crowded city and to link with commuter trains, light rail and the famous Underground.
      By any standards, the London public transportation network is immense. Below ground, 12 "tube" lines connect 270 stations. More than a dozen of these Underground stations are collection points for British Rail commuter trains serving outer suburbs. On London's maze of narrow streets, nearly 5,000 buses wind their way through 700 routes pausing to pick up and deliver passengers at 17,000 stops.
      Less obvious to the passengers is that these routes are operated by 30 independent bus companies, the result of a privatization effort in the 1980s. Although the routes have been privatized, the bus system is still managed centrally by a government agency - London Transport (LT), a corporation which also operates the Underground.
      Despite the prevalence of public transportation, London's streets are still choked with private vehicles. LT's ultimate goal, therefore, is to increase ridership and decrease personal vehicle traffic. As a result, LT is constantly altering and tweaking the system to make it more efficient.
      The primary objective in modifying the system is to create an integrated network in which the bus routes complement each other and feed the Underground and rail lines so that a passenger's travel time from the front door to the final destination is minimized. The promise of time savings and convenience plays a big role in luring passengers to public transportation.
      Constant modifications are required to keep pace with changing demographic and social factors. Increases in car ownership, neighborhood redevelopment and economic shifts are just a few factors that can necessitate new or altered transportation services.
      Keeping track of these demographic changes and modeling the transportation scenarios which they might affect is the job of the LT's service planners. In 1991, LT began developing a GIS to assist with planning projects. Development is spearheaded by the marketing department in conjunction with consulting advice from Genasys UK and Cray Systems (Transport and Telecoms Division).
      "We are developing the GIS to visualize the bus network and model its interaction with the Underground and British Rail," explained Janette Bowes, senior transportation planner in the LT marketing department. "Although all modes of transportation can be modeled with the GIS, we focus on the buses because it's easier and quicker to re-route a bus route than a subway or rail line."

Developing a Transportation GIS
In many ways, GIS technology is ideal for transportation system analysis because it can visualize and model relationships among several layers of information, such as different transportation modes and demographic groupings, explained London Transport's Bryn Lockwood, a GIS project manager.
      Despite the innate advantages of GIS, the marketing department was unable to find a commercial GIS product aimed specifically at the public transportation industry. As a result, it looked for a full-featured GIS product that could be easily customized to perform functions unique to transportation analysis studies.
      The department chose GenaMap GIS software, developed by Genasys II Inc. of Fort Collins, Colo. An overriding factor in the purchase decision was that GenaMap is an open system written with Bourne shell, a standard scripting language that enables virtually any computer programmer to create tailored algorithms that meet the needs of their specific applications. London Transport worked with the Genasys UK office in Manchester, England, to customize the software for its specialized transportation applications.
      GenaMap was also the only package that offered a complete suite of matrix functions. These allowed the transportation planners to build interaction matrices that can be used to measure non-linear distances, model traffic flows, and calculate shortest path routes between origin and destination points - critical capabilities in transportation analysis.
      "Transportation applications are dynamic," said Lockwood, "and they always have two ends, an origin and destination."
      Budget constraints have required the marketing department to populate the GIS gradually over several years. A digital street centerline map purchased from the U.K. Ordnance Survey serves as the GIS basemap. The department also bought a commercial street map and scanned it for use in locating street names and landmarks.
      Another department supplied an extremely accurate digital map of bus stop locations to overlay on the centerline map. Geographically accurate maps of the Underground, commuter rail and light rail lines have been georeferenced to the basemap. Complete descriptions of each bus stop and station have been added as attribute data.
      Demand Zone Maps form another important layer in the GIS. London Transport relies on periodic personal surveys conducted at bus stops and tube stations to determine exactly where its riders come from and where they are going. This information is consolidated into Demand Zone Maps which graphically illustrate origin points for riders at particular tube stations or bus stops.
      Census data maps are plotted in the GIS based on population density areas of about 200 households. Statistics for each of these areas include total population, percent of working age, percent of retirement age, car ownership, and unemployment figures.
      The marketing department maintains its data in an INGRES database which is accessed directly by the GIS via a built-in gateway. GenaMap stores data in a single format regardless of platform, which allows GIS model results to be transferred seamlessly from the Unix server to the NT personal computers used by the transportation analysts, the end users of the GIS information.

Transportation Analysis
On a daily basis, the GIS is used for simple query functions such as highlighting areas which are currently poorly served by public transportation. Such areas can be found by searching the GIS for locations which are farther than 400 meters from a bus stop. These queries supply the information needed for the planners to fine tune the details of the new routes they have devised.
      Many transportation planning projects, however, are much more complicated than simply finding a street corner that needs a bus stop. They often require weighing multiple social and geographic variables that can influence - or be influenced by - public transportation. The output from these models must be considered in terms of cost and benefits, which is where the GIS plays an important role.
      "Time-based information is our main need," said Bowes. "The GIS determines distance between origin and destination points. Multiplying that by the average human walking speed or average traffic speed on a given street gives us a time figure."
      Time is critical to the cost-benefit analysis, she explained, because of the old adage, "Time is money." Transportation analysts who take the time calculations from the GIS often employ time-to-money conversions to compare various scenarios and decide which offers the greatest overall benefit.
      One use of the GIS is to determine the negative impact on passengers that would result if an Underground station were closed. In such studies, the planners assume that people will try to travel the shortest distance from their house to reach a bus stop or alternate station. In a neighborhood, of course, this route is rarely a straight line. Virtually all distance calculations in the GIS, therefore, require use of the matrix functions to determine the most likely non-linear travel routes through the established network of streets.
     The GIS calculates the time statistics for a variety of walking routes that a person may have to take if their nearest station were closed. The analysts then references demographic data for the neighborhood to assign real cost figures to the additional walk time. This real cost information allows the analysts to weigh one transportation change scenario against another in economic terms.

Transportation Influences
Many transportation planning decisions are reactions to social or economic changes, but some decisions are enacted to create change, said Bowes. In those cases, the GIS is used to weigh social benefits that may have positive economic impact over the long term. Policy decisions may be made to stimulate areas by improving transport facilities.
      For instance, London has used the provision of public transportation to leverage new development in economically depressed areas by making them more accessible to workers and tourists. LT built a light rail system to its Docklands district to revitalize this waterfront area which had become run down and isolated from the rest of the city. London Transport is continually examining options for new feeder services and extensions into the area with the aim of improving accessibility for local housing and industrial development.
      Another way in which the GIS can be used for smaller scale initiatives is in the presentation of demographic data such as unemployment rates or cars per person. This information is used to support arguments for enhancing public transportation in the target area.

Future Applications
The marketing department's current activities focus on commuters traveling to and from work in the morning and afternoon, but Lockwood and Bowes agree the capability of the GIS to handle huge volumes of data will soon allow them to narrow the scope of their studies.
      "We will specialize our analysis to cater to specific rider groups," predicts Lockwood. "The GIS makes it easy to access and analyze very specific data."
      The database already contains much of the information needed to accomplish this. Tourists, for instance, travel very predictable routes from their hotels to the major historical attractions and museums around town. At about 7 p.m., for example, the visitors begin moving toward the famous theatre district. Almost as predictable are the retired citizens who like to visit the shopping districts at mid-day when most citizens are at work.
      "We can even alter the GIS to make time calculations from a pensioner's front door to the bus stop based on the slower walking speed of an elderly person," said Bowes.
      Work will continue to include more relevant data and to provide more gateways to external sources - one area of interest is in highway congestion. Data will be collected to analyze changes in land use patterns following new developments such as the extension of the Underground's Jubillee Line.
      Another step for London Transport and its GIS is to make that type of detailed ridership information available to the public.
      "People must have confidence in public transportation before they will use it," said Lockwood. "The GIS can give people information, and information gives people confidence."

About the Authors:
Tony Adams is sales director for Genasys UK in England. He may be reached in London at 44-1-372-468-767. Kevin Corbley is a freelance writer in Denver, Colo. He may be reached at 303-987-3979 or by e-mail at [email protected]

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