Aries van Beinum, PMC leader for Traffic and Roads at Witteveen+Bos, obtained his PhD at TU Delft on 20 December 2018 for his research into turbulence; disturbances in the flow of traffic (such as lane changes) that occur around entrance and exit lanes. The results of the research provide road designers with insights that will enable them to better anticipate the behaviour of road users in their designs.

There is an increased degree of turbulence around the entrance and exit lanes. This rise usually starts a few hundred metres before the entrance or exit lane and disappears a few hundred metres after that. Design guidelines therefore state that weaving sections must have a certain minimum length and that input and output lanes must be at a certain minimum distance from each other. The distances between access and exit lanes and the length of weaving sections are therefore based on the area around the entry or exit lane, which is subject to an increased degree of turbulence.

The research has shown that most lane changes take place close to the point where the lanes intersect. This suggests that drivers prefer to enter or leave the motorway as soon as possible. This behaviour takes place at entrance lanes, exit lanes and in weaving compartments. Since most lane changes take place close to the point, increasing the distances between entrances and exits or increasing the length of the weaving section will not, or only to a limited extent, lead to a lower degree of turbulence.

However, motorists do need sufficient time to plan the intended lane change before it is carried out. The length available for lane change planning in the design is therefore more important than the length of the road section where there is an increased degree of turbulence. The recommendation from Aries' research is therefore that the distance between the entrance and exit lanes and the length of the weaving section should be based on the length of that 'preparation path', rather than on turbulence.