Human Factors advies landelijke uitrol Dynamax

This report describes the Human Factors aspects of dynamic maximum speed limits (also called Dynamax). The Dutch road authorities have had several studies conducted on motorways, with Dynamax being implemented in order to increase safety
(lower speed limit in case of rain), throughput (lower speed limit in order to avoid shock waves), air quality (lower speed limit for less pollution) and for decreasing travel times (higher speed limit in case of low traffic intensity). The studies included large scale real life pilots, focus group sessions, questionnaires, a driving simulator study and workshops with experts. The effects of Dynamax on safety, throughput, pollution and sound levels are studied, as well as the experience, comprehensibility, support from road users for Dynamax and the actual driving behaviour as a response to the measures. Different types of measures and different reasons for adjusting the speed limit were used, allowing the road authorities to study the conditions under which road users are most willing and/or able to comply with the dynamic speed limits. On the basis of knowledge from all studies, Human Factors experts describe in this report how road users experience Dynamax and how dynamic speed limits should be designed in order to come to the best results.
This is described from the perspective that perceiving, understanding, being able and being willing are the crucial factors to come to the required behaviour. The most important conclusion is that road users increase their speed when this is allowed and decrease the speed when necessary, but in most cases the speeds do not approach the actual speed limit. The lower the speed limit, the less people adjust their speed to the actual speed limit. In this, the reason behind the decreased speed limit plays a crucial role, as well as the actual design and layout of the measures, with roads users being less willing to adjust their speed because of air quality. The advice is to show dynamic speed limits on the gantry signs above each lane, with electronic motto signs next to the road instead of argumentation signs above the road. Special attention in this report is paid to the national roll-out of Dynamax. In a national roll-out, Dynamax should be designed as ‘120 km/h unless indicated otherwise’. Dynamax should warn road users for all lower speed limits, for example also for snow, freezing rain or road works. For a national roll-out, it is important to improve the argumentation for throughput and air quality, to have regular speed enforcement, to indicate when a road user is driving on a Dynamax trajectory and when he is not, and to communicate on a large scale about the positive effects of Dynamax. A couple of Human Factors questions are mentioned that have not been answered and therefore – if Dynamax will be implemented on a larger scale - need to be answered in the short term.