Multi-objective optimization of average travel time for a metro line by considering both location and dispersion effects

Headways (i.e. the time period between the departure times of two consecutive transportation vehicles) is an important issue for urban railway companies. In this problem we are facing with two conflicting objectives, average passenger travel time and rate of carriage fullness. Until now different multi-response optimization procedure for solving this problem is studied but these approaches do not consider responses variance and covariance between them in optimization process. Therefore this research presents a modeling and solution approach based on discrete-event simulation and response surface methodology that not only puts average of response in satisfactory region but also try to minimize the variance of responses relative to noise variable and also consider covariance between them. In order to evaluate the performance of the proposed approach, Tehran metro line 4 has been assessed. The results show that the proposed approach is superior to existing techniques.