Factors contributing to urban expressway entrance and exit safety

In order to obtain the relationship between traffic safety and influencing factors such as entrance and exit design and facilities setting, this paper uses number of traffic conflicts to measure traffic safety, determines experimental factors, designs experimental method, and establishes simulation models based on SSAM with calibrated parameters to collect traffic conflict data under a series of experimental factors of different levels. The result includes: traffic conflicts at exit are more than that at entrance; the gradient of ramp has some but not apparent effect on traffic conflicts; lane change and deceleration in advance is most important for improving traffic safety, and is the most effective method to decrease number of traffic conflicts. The tendency the result shows is in accordance with previous accident data and qualitative analysis, and thus credible. Finally, the paper puts forward principles for expressway design and safety facilities setting.