Road traffic congestion sometimes happens at tunnel exit even without high traffic flow. One reason is that the deceleration process is imperceptible when the vehicle is driving to the tunnel exit with gradual upgrade slopes. Nowadays regulations are more concentrated in transport sectors, and control measures are applied to vehicles through the tunnel. This process is careless of vehicles’ specific characteristics and easily distract the driver attention.In this paper, a tunnel climbing acceleration reminder system is introduced. When the speed drop is detected and the analysis show this is due to the driver's unconscious behavior, the system will remind the driver to speed up.Based on the dynamic model and the tunnel properties, the relationship between the throttle opening degrees and the duration with the speed change is studied. Then, the engine braking is considered for the variation of speeds and slopes. Then combining the tunnel lighting effects on drivers, unconscious deceleration reasons is explored. The judgement criterion for the driver's unconscious behavior is determined. The geometric data and traffic flow data of the Wuhan Yangtze River Tunnel is used to verify the function of this system.The study shows that, during the start of morning rush and the end of evening peak, this on-board system could allow the average traffic congestion time dropped by 5-30%, which means higher traffic efficiency and comfort driving experience.