A Driving Simulator Study on Diverging Driver Performance Along Tapered and Parallel Deceleration Lane

Highway diverge areas are often characterized by high crash rates. All over the world, geometric design guidelines propose deceleration lanes with parallel or tapered layout in order to promote a free-vehicle condition, while neglecting the potential effects of traffic flow and risky driving behaviors that are induced by the wrong perception of road geometries and vehicle interferences. A driving simulation study is carried out to analyze the effects of traffic flow and deceleration lane geometries on the driving performance of diverging drivers. Two different types of deceleration lanes (parallel and tapered) are implemented in a simulator, and two different traffic conditions (low and high traffic flows) are simulated for each type. Thirty one drivers took part in the experiments. The effects of traffic flow on the driving performance whilst approaching the diverge area and during deceleration are investigated. The study found that lane type significantly affects the speeds of diverging drivers, independent of the traffic condition, with higher interferences with the through traffic on the tapered lane. Traffic condition was found to influence the driver’s trajectory along the tapered lane, and thus delaying the exiting maneuver under high traffic conditions. This effect was not found to be significant for parallel deceleration lanes on which, on the contrary, the deceleration rates were significantly affected by the traffic condition: higher decelerations were recorded under low traffic condition. No significant traffic effects on deceleration rates were found on the tapered lane.