Using gap sequences to estimate gap acceptance functions

Traditional gap acceptance functions have been estimated based on the first gap observed. In this paper we show that the critical gap of drivers is decreasing on the average, as they are waiting for an acceptable gap. Our gap acceptance function is based on a probit model which assumes a normal distribution of gaps across gaps and drivers.     

A note on the turn and arrival likelihood algorithms of traffic assignments

This note illustrates by means of examples that two of the three modifications of Dial's assignment algorithm suggested recently by Tobin (1977) should be subject to further research prior to implementation. Three potential problems with these algorithms are shown to be significant for small contrived networks.     

A comparison of stochastic and deterministic traffic assignment over congested networks

The similarity between link flows obtained from deterministic and stochastic equilibrium traffic assignment models is investigated at different levels of congestion. A probit-based stochastic assignment is used (over a congested network) where the conditions for equilibrium are those given by Daganzo and Sheffi (1977). Stochastic equilibrium flows are generated using an iterative procedure with predetermined step sizes, and the resulting assignment is validated on the basis of the equilibrium criteria. The procedure is intended to assist in the choice of the most appropriate assignment algorithm for a given level of congestion.     

Analytical model of traffic delays under bus signal preemption: Theory and application

Major emphasis has been placed in recent years on the improvement of the operations of existing transportation facilities, using Transportation Systems Management strategies. Accordingly, preferential treatment of high occupancy vehicles is playing an increasing role in transportation projects. This paper deals with one of these strategies, the priority treatment of buses at signalized intersections. Such treatment is aimed at improving the capacity of intersections. The paper develops an analytical model of delays at signalized intersections under a bus preemption scheme. The analysis is presented for the simplest case, i.e., two intersecting one-way streets. The results suggests that the benefits of bus preemption can be increased by properly adjusting several design parameters such as cycle and phase duration of the preempted phases as well as the non-preempted parameters. The model outlined in this paper is applicable to any situation in which stochastic variation is introduced into the signal cycle as well as to bus preemption. Consequently, other potential applications of the model include the design/analysis of traffic actuated signals, and pedestrian actuated signals.     

Estimating choice probabilities among nested alternatives

In several travel choice situations (e.g. automobile ownership level and trip frequency) the alternatives available to an individual randomly chosen from the population exhibit some internal choice-related ranking: the choice of a given alternative implies that all lower-ranked alternatives have been chosen. Such alternatives are referred to as “nested”. This paper presents a model for estimating choice probabilities among nested alternatives. The model is devised from the well known logit model and uses existing logit maximum-likelihood estimation techniques (and computer packages). The approach is shown to be more attractive than the multinomial logit and linear regression models, from a theoretical point of view, yet cheaper than the multinomial probit model. The model is developed in a disaggregate, utility maximization framework. An example application, estimating probabilities of trip frequencies by elderly individuals is presented.