Which is the more important for road safety—road design or driver behavioural adaptation?





accident rate, behavioural adaptation, feedback parameter, horizontal curve


Studies consistently show that sharp horizontal curves increase accident rate. One would therefore expect roads with many sharp curves to have a higher accident rate than roads with few sharp curves. This is not the case. The differences in road safety between roads with different profiles of horizontal road alignment are quite small. There are even studies suggesting that areas having roads with many curves have a lower number of accidents than otherwise identical areas with less curvy roads. The question arises: How can it be true both that sharp curves increase accident rate and that areas with roads with many sharp curves do not have a higher accident rate than areas with less demanding alignment? The answer is likely to be found in behavioural adaptation among drivers. The accident rates both in curves and on straight sections are strongly influenced by how drivers adapt behaviour to the number of curves per kilometre of road. This paper shows how behavioural adaptation can be quantified by means of the ‘human feedback parameter’ proposed by Evans. This parameter takes a value of -1 if drivers adapt behaviour so as to completely eliminate a risk factor. Values close to -0.7 for horizontal curves were estimated on the basis of micro-level studies. Thus behavioural adaptation reduces the increase in risk to about 30% of what it would have been without behavioural adaptation. In addition, a high frequency of curves leads to lower speed on the straight sections between curves.


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Author Biography

Rune Elvik, Institute of Transport Economics, Norway

Rune Elvik has been a road safety researcher at the Institute of Transport Economics since 1980. His main areas of research have been evaluation studies, meta-analysis and cost-benefit analysis.

Rune Elvik served as editor-in-chief (together with Karl Kim) of Accident Analysis & Prevention from 2005 to 2013. He has participated in many European projects and contributed to the Highway Safety Manual. He has published more than 150 papers in scientific journals.

CRediT contribution: Conceptualisation, Data curation, Formal analysis, Methodology, Writing—first draft, Writing—final review


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How to Cite

Elvik, R. (2022). Which is the more important for road safety—road design or driver behavioural adaptation?. Traffic Safety Research, 2, 000009. https://doi.org/10.55329/pvir7839