Effectiveness of static detour signage on motorways

Abstract

Several incidents involving the installation of temporary traffic signs by road workers have raised concerns about the effectiveness of these signs. Even in the absence of incidents, effectiveness is a relevant question, made more urgent by the incidents and the high risk of collision faced by road workers installing the signs. This paper investigated the influence of static traffic diversion signs on drivers' route choice and driving behaviour during road closures on secondary roads adjacent to motorways in the Netherlands. The influence of static diversion signs is assessed by analysing route choice, detour compliance and changes in driving behaviour, in terms of speed variations around diversion signs. In addition, the paper aimed to develop a detour behaviour model that classifies drivers into four different detour driver profiles. These profiles are developed based on potential route choices, driving patterns around road closures, detour behaviour factors and driving styles. Therefore, the four driver profiles are categorised as following the detour, not following the detour, choosing an alternative route and avoiding the closure area. This model provided a systematic framework for understanding detour route choices and shows the complexity of driver behaviour around road closures. Two case studies are evaluated by an observation study on route choice, detour compliance and speed adjustments around detour signs, during night-time road closures. The first case study was conducted near exit 9 Aalsmeer on the A9 motorway and the second near exit 27 Hagestein on the A27 motorway in the Netherlands. Observations from the A9 case study showed that 73.8\% of the road users heading towards the closed road do not comply with the detour signs during the closure phase, which accounts for 18.3\% of the expected traffic on the exit ramp. A more detailed analysis of route choice in the A27 case study showed a 33\% compliance rate with the detour. A significant proportion of road users (60\%) showed non-compliance by disregarding signs and taking the shortcut. In addition, a small percentage (4\%) did not initially follow the diversion but later returned to the motorway to comply, while a further 4\% chose to avoid the closed road area altogether. Therefore, the non-compliance rate across both case studies ranges from 64\% to 73.8\%. The results showed that static signs have a limited effect on diverting traffic to the detour. Moreover, there are no significant changes in speed around the signs found, supporting a limited effect on changing driver behaviour. The paper highlights the complexity of driver behaviour around road closures and demonstrates the limited effectiveness of static diversion signs in directing traffic to detours. These findings emphasised the importance of re-evaluating sign placement and it is recommended to explore and implement alternative methods of traffic control. This could include the use of dynamic, real-time information, such as smart traffic systems and mobile applications, to guide road users more effectively and improve the safety of road workers. Future research should focus on individual-level road user and factor analysis, the influence of navigation systems, and the effects of temporary traffic measures in different contexts to further refine traffic management strategies.