Discussion of “Model for Determining Optimum Bus-Stop Spacing in Urban Areas” by Anthony A. Saka

Abstract

The discusser appreciates the exhaustive studies undertaken by the author in developing the model for optimal spacing of bus stops. The writer fully concurs with the author that maximizing service objectives and minimizing fleet size are two conflicting issues. The discusser, however, has certain reservations on the direct applicability of the proposed model. The discusser fails to understand the computational utility of expression of the total lost time attributed to acceleration and deceleration, i.e., Ta,d as given in Eq. ~6!, for the estimation of the expected one-way travel time of bus, Tbus . To illustrate, substitute the value of To , from Eq. ~10b! in Eq. ~1!. This eliminates Ta,d , and thus, Tbus can be determined as Tbus5Ts1Tc1Tm1~ D/u! (1) Eqs. ~11! and ~14! can be simplified similarly, without affecting the results given in Table 1. This clearly demonstrates the nonrequirement of computation of the total lost time attributed to acceleration and deceleration, i.e., the expression for Ta,d given in Eq. ~6!. Further, for the total terminal-to-terminal distance D, the proposed model results in an optimal but fractional fleet size for a given number of bus-stop spacing x or for a given number of bus stops N. The discusser opines that it would be appropriate to work inversely on the problem for the estimation of the total number of bus stops or average bus-stop spacing for a nonfractional fleet size. The fleet size, therefore, may be optimized based on meeting the service objectives in terms of average bus-stop spacing or the number of bus stops for the total terminal-to-terminal distance D.