Effects of variable message sign on driver detours and identification of influencing factors

This study presents the results of an investigation made to determine the dominant influencing factors and their specific impacts on motorist detour making for variable message sign (VMS) placements on a freeway. This was necessary to provide engineers with a tool for evaluating VMS cost-effectiveness and feasibility. The research found that additional travel time delay is the most influential variable in determining motorist detour making. In addition, more than 70% of freeway motorists recognise adjacent national roads as detour routes and both average annual daily traffic and the distance to the entering point of the detour path are found to be dominating factors. A motorist detour ratio model as a function of VMS placement on a freeway was developed based on these observations. In the model validation, actual detour making behaviours observed by revealed preference values showed some discrepancies, but these were minimal. These research findings should be useful for cost-effective placement of VMS on freeways and it is recommended that the results be tested by practicing engineers in the intelligent transportation system sector.