Color Variable Speed Limit Sign Visibility for the Freeway Exit Driving Safety

Typical vehicle speed deceleration occurs at the freeway exit due to the driving direction change. Well conducting the driver to control the velocity could enhance the vehicle maneuverability and give drivers more response time when running into potential dangerous conditions. The freeway exit speed limit sign (ESLS) is an effect way to remind the driver to slow down the vehicle. The ESLS visibility is significant to guarantee the driving safety. This research focuses on the color variable ESLS system, which is placed at the same location with the traditional speed limit sign. With this system, the driver could receive the updated speed limit recommendation in advance and without distraction produced by eyes contract change over the dashboard and the front sight. First, the mathematical model of the drivetrain and the engine brake is built for typical motor vehicles. The vehicle braking characteristics with various initial speeds in the deceleration area are studied. And then the brake duration distributions for the engine brake and the wheel brake are scheduled for vehicles' characteristics. The recommended decelerate values are arranged and shown with the band color change corresponding to the real-time vehicle driving condition. Furthermore, the simulated driving environment was used to evaluate the validity of the color variable ELSE system by recording the vehicle motion trace, the velocity vector as well as the lane side boundary. The result shows that the color various ESLS could effectively conduct the vehicle deceleration process which is meaningful for the design of the future speed limit sign.