Impact of traffic congestion on road accidents: a spatial analysis of the M25 motorway in England.

Traffic congestion and road accidents are two external costs of transport and the reduction of their impacts is often one of the primary objectives for transport policy makers. The relationship between traffic congestion and road accidents however is not apparent and less studied. It is speculated that there may be an inverse relationship between traffic congestion and road accidents, and as such this poses a potential dilemma for transport policy makers. This study aims to explore the impact of traffic congestion on the frequency of road accidents using a spatial analysis approach, while controlling for other relevant factors that may affect road accidents. The M25 London orbital motorway, divided into 70 segments, was chosen to conduct this study and relevant data on road accidents, traffic and road characteristics were collected. A robust technique has been developed to map M25 accidents onto its segments. Since existing studies have often used a proxy to measure the level of congestion, this study has employed a precise congestion measurement. A series of Poisson based non-spatial (such as Poisson-lognormal and Poisson-gamma) and spatial (Poisson-lognormal with conditional autoregressive priors) models have been used to account for the effects of both heterogeneity and spatial correlation. The results suggest that traffic congestion has little or no impact on the frequency of road accidents on the M25 motorway. All other relevant factors have provided results consistent with existing studies.

[1]  D. Shinar,et al.  Aggressive driving: an observational study of driver, vehicle, and situational variables. , 2004, Accident; analysis and prevention.

[2]  Li Zhu,et al.  A GIS-based Bayesian approach for analyzing spatial–temporal patterns of intra-city motor vehicle crashes , 2007 .

[3]  Simon Washington,et al.  Important omitted spatial variables in safety models: Understanding contributing crash causes at intersections , 2007 .

[4]  D. Graham,et al.  Spatial Variation in Road Pedestrian Casualties: The Role of Urban Scale, Density and Land-use Mix , 2003 .

[5]  T. Golob,et al.  Relationships Among Urban Freeway Accidents, Traffic Flow, Weather and Lighting Conditions , 2001 .

[6]  Dominique Lord,et al.  Poisson, Poisson-gamma and zero-inflated regression models of motor vehicle crashes: balancing statistical fit and theory. , 2005, Accident; analysis and prevention.

[7]  T W Forbes,et al.  EFFECT OF AVERAGE SPEED AND VOLUME ON MOTOR-VEHICLE ACCIDENTS ON TWO-LANE TANGENTS , 1953 .

[8]  A H Rhodes,et al.  Speed, speed limits and road traffic accidents under free flow conditions. , 1999, Accident; analysis and prevention.

[9]  Y. MacNab,et al.  Autoregressive Spatial Smoothing and Temporal Spline Smoothing for Mapping Rates , 2001, Biometrics.

[10]  Rune Elvik,et al.  Laws of accident causation. , 2006, Accident; analysis and prevention.

[11]  J L Martin,et al.  Comparison of road crashes incidence and severity between some French counties. , 2003, Accident; analysis and prevention.

[12]  David J. Spiegelhalter,et al.  WinBUGS user manual version 1.4 , 2003 .

[13]  D Shefer,et al.  Congestion, air pollution, and road fatalities in urban areas. , 1994, Accident; analysis and prevention.

[14]  Bradley P. Carlin,et al.  Bayesian measures of model complexity and fit , 2002 .

[15]  Roger Bird,et al.  Exploring Relationship Between Safety and Consistency of Geometry and Speed on British Roads , 2006 .

[16]  Ahmed E. Radwan,et al.  Modeling traffic accident occurrence and involvement. , 2000, Accident; analysis and prevention.

[17]  D. Gwynn.  RELATIONSHIP OF ACCIDENT RATES AND ACCIDENT INVOLVEMENTS WITH HOURLY VOLUMES , 1967 .

[18]  M. Quddus.  Modelling area-wide count outcomes with spatial correlation and heterogeneity: an analysis of London crash data. , 2008, Accident; analysis and prevention.

[19]  Bani K. Mallick,et al.  ROADWAY TRAFFIC CRASH MAPPING: A SPACE-TIME MODELING APPROACH , 2003 .

[20]  J. Besag.  Spatial Interaction and the Statistical Analysis of Lattice Systems , 1974 .

[21]  I Made Brunner,et al.  Influence of Land Use, Population, Employment, and Economic Activity on Accidents , 2006 .

[22]  Malay Ghosh,et al.  Hierarchical Bayes GLMs for the analysis of spatial data: An application to disease mapping , 1999 .

[23]  V. Sisiopiku,et al.  Relationship Between Volume-to-Capacity Ratios and Accident Rates , 1997 .

[24]  Andrew P. Jones,et al.  District Variations in Road Curvature in England and Wales and their Association with Road-Traffic Crashes , 2007 .

[25]  Piet Rietveld,et al.  Congestion and Safety on Highways: Towards an Analytical Model , 1997 .

[26]  M. Quddus,et al.  A spatially disaggregate analysis of road casualties in England. , 2004, Accident; analysis and prevention.

[27]  Luis F. Miranda-Moreno,et al.  Effects of low sample mean values and small sample size on the estimation of the fixed dispersion parameter of Poisson-gamma models for modeling motor vehicle crashes: a Bayesian perspective , 2008 .

[28]  P. Jovanis,et al.  Spatial analysis of fatal and injury crashes in Pennsylvania. , 2006, Accident; analysis and prevention.

[29]  Dj Turner,et al.  Motorway accidents: an examination of accident totals, rates and severity and their relationship with traffic flow , 1986 .

[30]  Fred L. Mannering,et al.  The relationship among highway geometrics, traffic-related elements and motor-vehicle accident frequencies , 1998 .

[31]  J. Wielinski,et al.  Annual Meeting of the Transportation Research Board , 2010 .

[32]  Piet Rietveld,et al.  CONGESTION AND SAFETY ON HIGHWAYS. , 1994 .

[33]  Dominique Lord,et al.  Modeling crash-flow-density and crash-flow-V/C ratio relationships for rural and urban freeway segments. , 2005, Accident; analysis and prevention.

[34]  Robert B. Noland,et al.  Congestion and Safety: A Spatial Analysis of London , 2003 .

[35]  F Mannering,et al.  Effect of roadway geometrics and environmental factors on rural freeway accident frequencies. , 1995, Accident; analysis and prevention.

[36]  Moshe Livneh,et al.  Relationships between road accidents and hourly traffic flow—I: Analyses and interpretation , 1982 .

[37]  Dominique Lord,et al.  The prediction of accidents on digital networks, characteristics and issues related to the application of accident prediction models , 2000 .

[38]  J. Ivan,et al.  Explaining two-lane highway crash rates using land use and hourly exposure. , 2000, Accident; analysis and prevention.

[39]  Peter Cummings,et al.  Freeway speed limits and traffic fatalities in Washington State. , 2002, Accident; analysis and prevention.

[40]  Jeremy Woolley,et al.  Integration of the global positioning system and geographical information systems for traffic congestion studies , 2000 .

[41]  Luis F. Miranda-Moreno,et al.  Effects of Low Sample Mean Values and Small Sample Size on Estimation of Fixed Dispersion Parameter of Poisson-Gamma Models for Motor Vehicle Crashes: Bayesian Perspective , 2007 .

[42]  Jean-Louis Martin,et al.  Relationship between crash rate and hourly traffic flow on interurban motorways. , 2002, Accident; analysis and prevention.

[43]  Avishai Ceder.  Relationships between road accidents and hourly traffic flow—II: Probabilistic approach , 1982 .