Short-Run Route Diversion: An Empirical Investigation into Variable Message Sign Design and Policy Experiments

Variable message signs (VMSs) can convey several traffic and roadway information to motorists. Using empirical stated preference (SP) data from road users in Bangkok, Thailand, we demonstrate that short-run route diversion can be estimated and forecast based on different VMS message-content attributes via mixed logit and logit models in which the motorist's stated route diversion is the dependent variable. The findings reveal that different message contents lead to different levels of route-changing propensity. Route diversion in Bangkok is likely when a VMS displays a suggested route and qualitative information. The framing effect on route-choice decision explains the finding of qualitative delay information preference to its quantitative counterpart. To determine the policy implications, we further investigate the developed models by estimating changes in the probability of the stated route choice due to changes in the message content. Three VMS message policy experiments are conducted using the model: enforcing quantitative delay content, enforcing qualitative delay content, and enforcing suggested route content. The results show that qualitative delay information and the suggested route reduce the ambiguity of the message quality. The optimal VMS designs for short-run traffic management to encourage/discourage route diversion are discussed.