Estimation of Legibility Distance for Portable Variable Message Signs

Abstract

Variable Message Sign (VMS) is one of the major components of intelligent transportation systems (ITS), which is useful for providing real-time information on weather, traffic and highway conditions. In particular, portable variable message signs (PVMS) are very useful in managing traffic events including work zone, special events, and incidents. It is essential that PVMS locations and message operations should be designed with the proper consideration of driver's legibility distance. A variety of factors would affect the legibility distance, such as drivers' travel speed and driver characteristics etc. This study aimed at establishing a functional relationship between legibility distance and causal factors based on extensive field experiments. A specially manufactured PVMS was used for the experiment. A 500-meter tangent segment having 4 lanes (2 lanes for each direction) was selected for field experiments at the Hanyang University at Ansan, Korea. A differential global positioning system (DGPS) in a control vehicle was used to obtain drivers' legibility distances. Data collection and analysis were undertaken to develop an estimation model for the drivers' legibility distances using regression modeling techniques. The proposed model would be greatly useful for ITS designers and planners when making decisions on PVMS locations and message operations for better traffic management.