Using Behavioural Measures to Evaluate Route Safety Schemes
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Using behavioural measures to evaluate route safety schemes Guidance for practitioners By H A Ward, S Helman, N Christie, F P McKenna CPR102 9 1 1. Context: The need for evaluation Route safety schemes are complex interventions which may involve more than one agency. They use multiple methods to reduce the number of casualties along sections of road by changing driver behaviour through elements of engineering, education and enforcement. Evaluation is the mechanism by which the effectiveness of the intervention is assessed in achieving its objectives. Route safety schemes bring new challenges in the form of developing the best way to evaluate their effectiveness. 1 This note is a short guide for practitioners on using behavioural measures to evaluate route safety schemes. http://www.adeptnet.org.uk/assets/userfiles/documents/000282.pdf Above is a link to the location of the main report (which should be read in conjunction with this guide) to direct readers to a fuller description of: the top candidate behaviours which should be considered as relevant to route safety schemes; how to measure the impact of a scheme through changes in these behaviours; the key issues related to the design of interventions including how to define what „success‟ looks like, how to develop a cost effective monitoring programme and how to analyse and interpret data so that a robust conclusion can be drawn from the evaluation; and case studies of good practice from local authorities. 1 The first author drafted this guidance document based on the accompanying main report. The remaining authors are listed in the same order in which they appear on the main report. This order was determined randomly. All four authors worked together and contributed in equal measure to the content of the main report (on which this guidance document is based) and its recommendations. 1 In addition to road safety, schemes can have wider objectives, so a set of metrics is essential to a rounded and robust evaluation of the impacts across a number of objectives such as: a reduction in: o the number of casualties o the number of people exceeding the speed limit o the number of people close following o the number of people using mobile phones while driving o the number of people overtaking o the number of people driving whilst impaired through alcohol, drugs or fatigue o the number of people driving without licences, tax or insurance o social exclusion an increase in: o seat belt wearing or child restraint use o knowledge of road safety messages o community involvement Why monitor behaviour? Evaluation using behavioural outcomes provides evidence to the road safety team regarding whether to: continue the intervention or stop it; expand or reduce it; or modify it or leave alone. 2 Assessing the impact of a route scheme on the occurrence and severity of casualties is an important element in evaluating its effectiveness but numbers are often small and collision sites scattered along a route, rarely clustering at locations in numbers large enough to apply specific engineering measures. The traditional approach of assessing three years before data with three years after data may mean that, given the high variability inherent in small numbers, emerging problems are not spotted quickly enough to intervene to prevent further collisions and injury. Measuring changes in road user behaviour gives the evidence needed to enable the detection of impacts of interventions over short timescales. This can include evidence that behaviours are changing as intended, or whether there are unintended consequences that lead to increases in casualties or unwanted road user behaviours. While it is generally acknowledged that practitioners act with the best of intentions there has been a tendency for some in road safety to design interventions on the basis of „enthusiastic intuition‟ or the overall plausibility of the intervention, neither of which provide a guarantee of success. Evaluation is not an optional activity, separate from the key task of producing a successful intervention; it is not an alternative or competitor to more implementation. It is the core provider of evidence to aid learning from experience of what works and what doesn‟t for designing and implementing future schemes and for assessing cost effectiveness of current schemes. Evidence obtained through reliable evaluation can underpin the justification for route safety programmes and support bids for future funding. Measurement of behavioural variables can help to establish the effects of route safety treatments over relatively short timescales 3 2. Which behaviours and attitudes should be measured and by what means? It has been clear for some time that human factors and road user behaviour play an important role in accident involvement. The key questions that need to be answered are: 1. Which human factors / behaviours play a role? 2. What is the evidence relating them to collision risk? 3. How can they be measured? Human factors are known to play a role in collisions In this guide, a concise set of answers is provided to these questions. Importantly, the aim is to include only human factors that are known (or very strongly suspected) to be related to accident risk. The intention is to focus practitioners‟ attentions (when designing interventions and when evaluating them) on behaviours that are most likely to lead to safety outcomes. There are a number of behaviours that are either known or strongly suspected to be linked to collision risk. In this guide and the main report, such behaviours are listed as candidate behavioural metrics for use in the evaluation of route safety schemes. The behaviours are split into a taxonomy based on whether they need to be measured by observing (on the route in question) vehicles or drivers/road users, or by talking directly to road users who use the route. The main report reviews the evidence linking these behaviours to collision risk and the methods by which they can be measured are outlined. 4 Table 1 summarises these Table 1: Measurable behaviours involved factors associated with in collision risk or influencing the collision risk and the severity of the outcome relative ease with which Observable behaviour that can be the authors believe they measured from vehicles can be measured within a route safety context. Easier to measure Speed One important point to make is that the authors Speed profile are advocating the measurement of Following distance behavioural and attitudinal variables directly; this Overtaking allows practitioners to get a direct handle on the Gap acceptance causal mechanisms by which drivers and road More Lateral position users on a given route difficult to measure may be increasing (or decreasing) the risk of Observable behaviour that can be accidents. measured from drivers Obviously not all these behaviours need be Easier to Unlicensed and uninsured driving measured for each scheme measure but the choice of Mobile phone use and other distractions appropriate ones will give an indication of how Seat belt use progress towards achieving a variety of More Fatigue and impairment objectives can be assessed difficult to (see Section 3 in main measure report and following in this Non-observable attitudes and behaviour guide). that can measured from drivers The measurement of Attitudes regarding specific behaviours behaviours in the table are especially violations briefly summarised below with more information in Attitudes regarding interventions the main report. especially perceived likelihood of detection and collision risk 5 The evidence for the relationship between speed and collision involvement is well known and its measurement is routine for Local Authorities (the Road Safety Good Practice Guide gives details – see Section 5 in main report). Other behaviours which can be measured from observing vehicles include speed and journey time over the route which are relevant to assessing measures to reduce speed along the route. By the use of instrumented cars and a range of drivers, profiles of deceleration and acceleration can be obtained which are useful in assessing effectiveness of programmes to reduce „harsh‟ driving styles that have been linked to collision involvement. Close following is an aggressive driving style with links to collision involvement. Following distance is known as headway and is measured in distance or time from the front of (leading) Vehicle A to the front of (following) Vehicle B. It is usually measured using loop detectors (some speed measuring devices have this facility) but can also be undertaken with a stop watch and a reference point at the Close following is known to be related side of the road to collision involvement People who commit driving violations are more likely to be involved in collisions. Tendency to commit violations and self reported rates can be measured by using a questionnaire which can be found in the appendices of the main report. Red light running can be measured directly. Injudicious overtaking is associated with collision risk as it exposes drivers to head-on collisions. It can be measured by observation and speed measurements. It is commonly accepted that if drivers were to increase the size of gaps they accept when turning across or joining traffic, safety would improve. It is usually measured by filming vehicles and measuring the size of gaps accepted and rejected. 6 Lateral position on the carriageway may be relevant to determining risk of head on and run- off collisions, especially at bends. It can be measured on-site using filmed footage though this is labour intensive. Hazard perception is related to collision risk and distraction – including mobile phone use reduces the ability of drivers to detect hazards. Video photography and still photography are potential techniques though the most straightforward might be road side observation of the numbers of drivers using phones, eating, and interacting with in-car technology. In-car distractions are an important risk factor for road accidents Fatigue leads to sleep related collisions which often have serious consequences but this is the behaviour perhaps most difficult to identify and measure.