The effects of roundabouts on accidents with bicyclists: influence of the design type of cycle facilities XXth ICTCT-workshop - 26 October 2007 Valencia, Spain Stijn Daniels 1, Tom Brijs 1, Erik Nuyts 2, Geert Wets 1 1 Hasselt University 2 Provincial College Limburg - Belgium stijn.daniels@uhasselt.be
Outline Introduction Data collection Methodology Results Conclusions
Introduction Roundabouts generally improve traffic safety (Elvik et al., 2003; Persaud et al., 2001) Accident rates for bicyclists higher (UK, FR, NL, BE) Limited amount of research about effects on particular types of road users, e.g. bicyclists Schoon & van Minnen (NL) (1993): effect for bicyclists weaker, but still favourable Research questions: 1. safety effects for bicyclists different from effects for all road users? 2. Influence of some geometrical/location features
Data collection (1) roundabouts Flanders-Belgium Constructed 1994-2000 Injury accident data 1991-2001 Comparison group of 172 intersections
Data collection (2) Number of accidents considered Roundabout locations Comparison group slight 314 486 Severest injury serious 142 fatal 7 21 TOTAL 411 649
Design types of cycle facilities Mixed traffic Cycle lanes Separate cycle paths Grade-separated
Data collection (3) Cycle facilities Type of cycle facility 1 MIXED TRAFFIC 2 CYCLE LANES 3 CYCLE PATHS 4 GRADE SEPARATED TOTAL Number of locations 9 40 38 3
Methodology Before and after study with comparison group (" Empirical Bayes) Controlling for General trends in traffic safety Regression to the mean No controlling possible for specific effects on traffic volume. Step 1 = effect (index) per location. Step 2 = meta-analysis. Step 3 = regression analyses on resulting effectiveness-indices.
Results N= Nr of locations Nr of accidents Best estimate [CI] effectiveness-index (<1 = decrease of accidents; >1 = increase) All accidents 411 1.27 [1.00-1.61] (*) Accidents with fatally or seriously injured 97 1.44 [1.00-2.09] (*) 1.42 [0.99-2.05] (ns) 1.42 [0.99-2.03] (ns) ns = non significant, * = p" 0.05 fixed k = 10-10 k= k_all accidents k= 10 10
Influence of design/location variables (1) Regression of (transformed) effectiveness-indices LN(EFF) upon known variables (type of cycle facility, replacing signals, inside/outside built-up area, ) Stepwise OLS linear regression (SAS-proc REG) Regression both for all accidents as accidents with killed or seriously injured
Independent variables Influence of design/location variables (2) Variable Description Type N INSIDE 0 = outside built-up area; 1= inside built-up area MIXED 0 = no mixed traffic; 1= mixed traffic CYCLLANE 0 = no cycle lane; 1 = cycle lane CYCLPATH 0 = no cycle path; 1 = cycle path GRADESEP 0= no grade separation; 1 = grade separation SIGNALS 0 = no traffic signals; 1 = traffic signals before roundabout construction RED 0 = not coloured, 1 = red-coloured bicyclist facilities (not applicable when MIXED = 1) 81 TWOLANES 0 = 1 lane; 1 = 2 lanes on the roundabout LINE 0 = no marking; 1 = marking between carriageway and cycle lanes (only in case of cycle lanes) 40 BARR 0 = no physical element; 1 = physical element between roundabout and cycle lanes (only in case of cycle lanes) 40 PRIOR 0 = no priority for bicyclists; 1= priority when crossing exit or entry lanes (only in case of cycle paths) 38
Influence of design/location variables (3) Regression results for all roundabouts, all accidents (N=) Variable Parameter Estimate Standard Error t Value Pr > t Standardized Estimate Intercept -0.52716 0.14166-3.72 0.0004 0 CYCLLANE 1.06098 0.18936 5.60 <.0001 0.51560 SIGNALS 0.50107 0.23468 2.14 0.0356 0.20726 TWOLANES 0.52040 0.36639 1.42 0.1591 0.13631 R² = 0.2953 F = 12.01 s = 0.88
Influence of design/location variables (4) Significant variables in other models: All acc., all roundabouts: CYCLLANE (+), SIGNALS (+) All acc., cycle lanes: SIGNALS (+) All acc., cycle paths: TWOLANES (+) KSI acc., all roundabouts: INSIDE (+) KSI acc., cycle lanes: INSIDE (+) KSI acc., cycle paths: \
Preliminary conclusions At least for the studied sample, converting intersections into roundabouts did increase the number of severe bicyclists accidents; Roundabouts with cycle lanes perform worse (in terms of injury accidents) compared to other design types; Some features tend to contribute to a worse performance: Traffic signals in before situation Location inside built-up area Two-lane roundabout Further research needed Oher countries Causal mechanisms Remedial measures