In contraflow work zone areas, traffic of one carriageway is guided to the other carriageway with decreased lane width, either partially (3-1 type work zone) or completely (4-0 type work zone). According to the Dutch guidelines for work zone areas, a contraflow system is only allowed to have a maximum length of 4 km, since otherwise it is supposed that road users experience too high a workload. The present study investigated the effects of long contraflow systems (up to 12 km) on lateral position, longitudinal control, speed, road marking crossings, steering performance, workload and subjective evaluation. The study included a driving simulator study, video observations of traffic behaviour at contraflow systems, and a study with an instrumented vehicle at prolonged contraflow-systems. The driving simulator study investigated the effect of type of contraflow system, lane width and length of the contraflow system on driving behaviour, workload and subjective safety. Video images of traffic behaviour at transitions from a standard motorway to both contraflow systems were analysed and effects of both contraflow systems on real driving behaviour and physiological measures were studied by means of driving in an instrumented vehicle in actual traffic. The three separate studies showed to be complementary. The driving simulator study (with simulated cars and heavy vehicles surrounding the subject) showed a clear difference in driving behaviour and subjective safety between 3-1 and 4-0 type work zones. Lane width also turned out to affect driving performance. The study with the instrumented vehicle showed effects on driving behaviour and physical workload, with the effect of length being in correspondence with the results found in the driving simulator study. The video images showed high turbulence in the traffic flow in front of the work zones due to a fairly high amount of lane changes. This may be explained by drivers trying to avoid the traffic lane where heavy traffic is allowed. Based on the results of the three studies together, safety recommendations were proposed for designing safe contraflow systems, with attention paid to lane width, type of work zone system and length of the work zone. (Author/publisher)
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