Historically, in all but the largest cities, transit planners would typically commit to a service plan using large buses on fixed routes over large sections of the agency's service area. As the travel needs and patterns within metropolitan regions continue to get more complex, it becomes necessary to provide more complex transit operations to meet these wider variety of needs. While traditional methods of service operations still work and need only relatively minor enhancements, there is a huge latent demand for transit service in smaller cities and modern auto-oriented suburbs. At the same time, there is community pressure to use limited operations budgets in both the most effective and efficient manner to meet these often conflicting requirements.
This paper describes a service planning concept based on the existence of a spectrum of possible service designs, ranging from pure fixed route design to pure demand-responsive design with many intermediate options. ITS technologies and scheduling software have matured to the point that it is now realistic to provide and plan transit services in this manner.
One planning option to consider for demand-responsive services is by time of day. Demand-responsive services are traditionally structured as an entirely separate service organization. Using ITS technologies, these services could be part of a spectrum of service designs under one operating budget. Looking at numerous options, it might be acceptable to somewhat degrade the performance of one service if it is offset by improvement in another. For example, if demand along some fixed routes is below a certain threshold during mid-day or in the evening, switching to Route-Deviation Service may relieve the cost of pure demand-responsive service while providing the additional important benefit of simultaneously mainstreaming some ADA-eligible riders. Experience with the Omnilink system in Prince William County, Virginia suggests that with less than 20 passengers per hour adding 10 minutes of slack time allows accommodation of one or two deviations per hour for routes taking approximately 35 minutes to drive without deviations. (1)
(1) Bruun and Marx 2006 "OmniLink – A Case Study of a Successful Flex-Route Capable ITS Implementation", Transportation Research Record, forthcoming.
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