Sources of error in road safety scheme evaluation: a quantified comparison of current methods.

This paper considers the various factors that can have a confounding effect in the evaluation of road safety schemes and examines the extent to which current methods can effectively deal with these. A modification to current methods is proposed which allows the reduction in accidents attributable to risk and flow changes to be separately evaluated. Data are presented to demonstrate the relative magnitudes of the various sources of error. It is shown that a principal source of error is normally regression-to-mean (RTM) and a correction for this effect should always be applied. Changes in traffic flow can also result in substantial accident changes and it is important to establish whether flow changes have occurred and if they are attributable to the effect of the scheme.

[1]  M J Maher,et al.  A comprehensive methodology for the fitting of predictive accident models. , 1996, Accident; analysis and prevention.

[2]  I. Summersgill,et al.  Accidents at urban priority crossroads and staggered junctions , 1996 .

[3]  Ezra Hauer,et al.  OBSERVATIONAL BEFORE-AFTER STUDIES IN ROAD SAFETY -- ESTIMATING THE EFFECT OF HIGHWAY AND TRAFFIC ENGINEERING MEASURES ON ROAD SAFETY , 1997 .

[4]  R Elvik,et al.  Evaluations of road accident blackspot treatment: a case of the Iron Law of Evaluation Studies? , 1997, Accident; analysis and prevention.

[5]  Bg Heydecker,et al.  A cost recovery system for speed and red-light cameras: two-year pilot evaluation. Research Paper, 11 February 2003, Department for Transport , 2003 .

[6]  I Summersgill,et al.  NON-JUNCTION ACCIDENTS ON URBAN SINGLE-CARRIAGEWAY ROADS , 1996 .

[7]  Linda Mountain,et al.  THE EFFECTS OF TREND OVER TIME ON ACCIDENT MODEL PREDICTIONS , 1997 .

[8]  Rune Elvik,et al.  The importance of confounding in observational before-and-after studies of road safety measures. , 2002, Accident; analysis and prevention.

[9]  L Mountain,et al.  Accident prediction models for roads with minor junctions. , 1996, Accident; analysis and prevention.

[10]  United Kingdom. Welsh Office,et al.  Road accidents Great Britain 1995 : the casualty report , 1996 .

[11]  Linda Mountain,et al.  IMPROVED ESTIMATES OF THE SAFETY EFFECTS OF ACCIDENT REMEDIAL SCHEMES , 1998 .

[12]  E Hauer,et al.  Overdispersion in modelling accidents on road sections and in empirical bayes estimation. , 2001, Accident; analysis and prevention.

[13]  Rune Elvik,et al.  Effects on Accidents of Automatic Speed Enforcement in Norway , 1997 .

[14]  Patrick S. McCarthy,et al.  Effect of speed limits on speed distributions and highway safety: A survey of recent literature , 2001 .

[15]  D C Webster,et al.  REVIEW OF TRAFFIC CALMING SCHEMES IN 20 MPH ZONES , 1996 .

[16]  L Mountain,et al.  The influence of trend on estimates of accidents at junctions. , 1998, Accident; analysis and prevention.

[17]  Ezra Hauer,et al.  Estimating Safety by the Empirical Bayes Method: A Tutorial , 2002 .

[18]  S. T. Buckland,et al.  An Introduction to the Bootstrap. , 1994 .

[19]  Ezra Hauer,et al.  Observational Before-After Studies in Road Safety , 1997 .