Abstract: The study on the risk characteristics of drivers′ behavior in extralong highway tunnel is very important. Hence, the realvehicle test is conducted in two typical extralong tunnels and the speed data of experienced and inexperienced drivers are collected simultaneously. Taking the data as subjective expected speed, the method of the quantified risk of drivers′ behavior is proposed based on the safe vehicle speed difference combined with the objective safe speed in driving environment. On the basis of dividing the tunnel section into the entrance section, the driving section and the exit section, the behavior risk variation characteristics of the two types of drivers in the entrance section and the behavior risk variation curves of the whole tunnel section and the ordinary highspeed section are compared and analyzed by dividing the driving section. The results show that: (1) In the tunnel, compared with the inexperienced driver, the experienced driver shows a higher behavioral risk. (2) Outside the tunnel, the risk is higher for inexperienced drivers. (3) All types of drivers have the highest behavioral risk in the normal highspeed section and the lowest in the tunnel entrance section. The above results indicate that in the tunnel section, the speed behavior of drivers familiar with the test road is not safe and the behavioral risk value is relatively high.

Key words: traffic safety, extralong highway tunnel, driver behavior risk, realvehicle test, safe speed difference