ABSTRACT
Fixed route and route-deviation are among the possible strategies of operating intra-urban transit. The route-deviation strategy requires vehicles to follow a basic fixed route and deviate from the route to offer doorstep service to passengers on request. Thus a combination of fixed route captive passengers and those desirous of doorstep service are carried. A theoretical comparison of fixed route and route-deviation strategies is undertaken, with a view to determine under which conditions one strategy could be preferable to the other. The objectives guiding the comparison are minimisation of total system cost and maximisation of operators profit. Models for total system cost per passenger and profit per passenger are set up and the optimum headways that best satisfy the chosen objectives are determined for each strategy. The deviation distance travelled during a trip is assumed to be a random variable with its probabilistic structure depending on the distribution of doorstep demand points in the service area. However, investigation of some specific situations indicate that, under low doorstep demand conditions, the deviation distance travelled in a trip is proportional to the total number of passengers carried. By parametrically varying demand, the effects of rider ship demand on the relative capabilities of the strategies under the two objectives are investigated. The general results are illustrated with a. numerical example focussed on the one-tomany and many-to-one 0-D travel patterns.It has been found that the optimum headways which minimise total system cost are sensitive to the relationship assumed between user generalised time cost and user generalised time. In general, it has been found that frequent service should be provided at high levels of demand and infrequent service at low levels of demand. For the route-deviation strategy, optimal headways and hence total system cost per passenger are also affected by the 0-D travel pattern and the proportion of passengers desirous of doorstep service. When the 0-D travel pattern is one-to-many, adopting the route-deviation strategy results in higher total system cost per passenger than for the fixed route strategy irrespective of whether a linear or quadratic relationship is assumed between user generalised time cost and user generalised time. For the many-to-one 0-D travel pattern, adopting the route-deviation strategy results in about equal or lower total system cost per passenger than for the fixed route strategy when demand levels are lower than about 37 passengers per hour (or the equivalent of 9.25 passengers per square kilometre per hour) and about 50 passengers per hour for situations where the relationships between user generalised time cost and user generalised time are linear and quadratic respectively. For given route configuration and fare levels, profit is maximised by adopting a headway which assures full vehicle load at the point of maximum load. The route deviation strategy appears to yield higher profit per passenger than the fixed route strategy when the doorstep service fare exceeds one-third and two-third of the fixed route fare for taxicab operation and minibus operation respectively.