Skid resistance, or road slipperiness, can affect the grip between vehicle tyres and the road and consequently the ability of drivers to maintain control of their vehicles. Skid resistance varies depending on road conditions and is most often an issue when roads are wet. Currently in New Zealand, locations where skid resistance is lower than desired are signposted by either an orange sign for temporary situations, such as roadwork activities, where skid resistance is reduced, or a yellow sign for situations where non-temporary conditions, such as climatic conditions (wet, ice, shading etc.), can reduce surface friction. Research (e.g. Charloton 2006) has suggested the signs currently used in New Zealand to warn drivers of lower than desired road surface friction are not well understood. With changes to the NZTA T10 specification in 2010, increasing the range of curves and raising the minimum standards for sideway force coefficient routine investigation machine (SCRIM) investigatory levels for high-risk curves, the number of areas identified as having lower than desired skid resistance has increased. The NZ Transport Agency (‘the Transport Agency’) therefore identified the need to develop a consistent, understandable and cost-effective way of warning drivers of the potential for lower skid resistance in both these areas and other areas that are renowned for periodic slippery conditions. To develop such an intervention, the Transport Agency required the investigation of drivers’ detection, comprehension and behavioural responses to traffic control devices intended to communicate to drivers that a road does not have the desired road surface friction and/or may be slippery under certain conditions. This would allow the development of recommendations as to how best warn drivers of these potentially hazardous conditions and encourage condition-appropriate driving behaviour in both short-term (temporary) and ongoing (more permanent) slippery road situations. The goal of this research project was to investigate drivers’ detection, understanding and behavioural responses to traffic control devices intended to communicate deficiencies in road surface friction to drivers, and to develop a consistent and understandable way of warning drivers of the road surface friction deficiencies in adverse conditions. To achieve this goal, the researchers had the following objectives: • Review the existing international and New Zealand literature and assess current best practice examples of signage used to indicate lower than desired road surface friction. • Investigate issues of detection and comprehension with existing signage as well as suggested alternatives. • Investigate driver behaviour in response to selected signage designed to communicate lower than desired road surface friction. • Collate, integrate and workshop quantitative and qualitative findings in order to deliver recommendations on how best to warn drivers that the road surface friction is below the New Zealand investigatory level and encourage appropriate driving behaviour. The research work consisted of four main stages, aimed at addressing the objectives identified in section 1.1: • Stage 1: A detailed and critical literature review of relevant literature and best practice. This involved identifying how road surfaces below the investigatory level are currently signposted in international jurisdictions using both static and dynamic signage and the level of comprehension and detection associated with these signs; identifying the human factors principles found to influence road sign comprehension and detection; reviewing measures used to empirically investigate the impact of different road surface signage; and examining the impacts of signage on driver behaviour. • Stage 2: Interactive workshops. This involved conducting two workshops. The first served to elicit qualitative data from the public on issues of detection and comprehension with existing signage, as well as the suggested alternatives (developed from the literature review), and to investigate the potential impact of each sign type on anticipated driver behaviour. The second involved an interactive session with the Steering Group to elicit expert opinion on the current and alternative signage and to contrast this with the public’s opinions and preferences in order to shortlist signage designs for on— road testing. • Stage 3: On- road trials of shortlisted signage options. This involved on-road testing to objectively measure the impact of the selected signage options on real-world driving behaviour, including driver speed, and workshopping a set of draft recommendations with the Steering Group to ensure recommended signage options are appropriate, practical and implementable. • Stage 4: Final reporting. This involved incorporating findings from the qualitative and quantitative studies and final workshop, with an emphasis on providing recommendations to the Transport Agency for the consistent use of signage indicating road surfaces that are below the investigatory level for surface friction. Chapter 1 of this report introduces the project and the research objectives. Chapter 2 describes the literature review findings. Chapter 3 describes the interactive workshop methods and results Chapter 4 describes the on-road trials methods and results Chapter 5 integrates the findings from chapters 3 and 4 and sets out a series of recommendations for the consistent use of signage indicating road surfaces that are below the investigatory level for surface friction. The appendices give further details of tools used and statistical analyses conducted. (Author/publisher)
Samenvatting