Drivers’ crossing behaviour between express and local lanes with soft separation: a driving simulator study

In different countries, hard separation is adopted as a technique to separate express and local lanes. However, in case of an incident, especially on the express lane, traffic jams can occur as there is no escape route. Emergency services are then required instantly to remove the obstruction. In some cases, even traffic diversion needs to be organized leading to time loss and which may possibly also affect the traffic in adjacent lanes. In this paper, an alternative flexible geometric design approach called ‘soft separation’ is evaluated having less side-effects in case of such calamities. A virtual environment using a driving simulator is used to evaluate 4 different types of soft separation. More specifically, driver behavior and driver temptations to cross different types of soft separation on the express lane are studied. These include: (1) a solid double line (2) cross hatch marking (3) tubular delineators and (4) vegetation / grass strip. Moreover, for each of the soft separation types, drivers were exposed to two different traffic conditions. In the first traffic condition, other vehicles in front did not cross the separation from express to local lanes whereas in the second condition, they did so. Results indicate that tubular delineators and the vegetation strip are more effective in restricting drivers to cross the separation. Implications for road design practice are given.