Investigation of drivers' diversion responses to urban freeway variable message signs displaying freeway and local street travel times

This paper explores urban freeway users' diversion responses to D-VMS (a new type of freeway variable message sign that explicitly provides travel times for both freeways and local streets) in the context of China. An on-site stated preference questionnaire survey was conducted to collect behavioral data. Four types of binary probit models were estimated to identify the factors that influence diversion behavior: the model with only constant coefficient and the models with normal', truncated normal', and log-normal' random coefficients. The three models with random coefficients accommodate heterogeneous preferences for travel time savings among drivers. The study shows that drivers' en route decisions on diverting from a freeway to local streets can be significantly influenced by D-VMS and the extent of the D-VMS impacts depends on driver characteristics, local street characteristics, and D-VMS messages. Main findings regarding D-VMS impacts are (1) travel time savings and drivers' years of driving experience serve as positive factors in diverting and (2) the number of traffic lights on the street, frequency of urban freeway use, being a mid-age driver, and an employer-provided car driver serve as negative factors in diverting. In terms of heterogeneous preference modeling, likelihood ratio tests show the three models with random coefficients obtain higher goodness of fits, and preliminary evidence is given that a small portion of drivers are insensitive to travel time savings indicated by D-VMS and persist in using urban freeways. The findings of this study have implications for the design and operation of D-VMS and for further effort on driver behavior modeling.