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1、Safety55.1Introduction1035.2Conflicts1045.2.1Vehicle conflicts1055.2.2Pedestrian conflicts1085.2.3Bicycle conflicts1105.3Crash Statistics1115.3.1Comparisons to previous intersection treatment1115.3.2Collision types1135.3.3Pedestrians1175.3.4Bicyclists1205.4Crash Prediction Models1225.5References125E
2、xhibit 5-1.Vehicle conflict points for “T” Intersections with single-laneapproaches.105Exhibit 5-2.Vehicle conflict point comparison for intersections withsingle-lane approaches.106Exhibit 5-3.Improper lane-use conflicts in double-lane roundabouts.107Exhibit 5-4.Improper turn conflicts in double-lan
3、e roundabouts.108Exhibit 5-5.Vehicle-pedestrian conflicts at signalized intersections.109Exhibit 5-6.Vehicle-pedestrian conflicts at single-lane roundabouts.109Exhibit 5-7.Bicycle conflicts at conventional intersections (showing twoleft-turn options).110CONTENTSFederal Highway Administration102Exhib
4、it 5-8.Bicycle conflicts at roundabouts.111Exhibit 5-9.Average annual crash frequencies at 11 U.S. intersectionsconverted to roundabouts.112Exhibit 5-10.Mean crash reductions in various countries.112Exhibit 5-11.Reported proportions of major crash types at roundabouts.113Exhibit 5-12.Comparison of c
5、ollision types at roundabouts.114Exhibit 5-13.Graphical depiction of collision types at roundabouts.115Exhibit 5-14.Crash percentage per type of user for urban roundabouts in 15 townsin western France.116Exhibit 5-15.British crash rates for pedestrians at roundabouts and signalizedintersections.117E
6、xhibit 5-16.Percentage reduction in the number of crashes by mode at 181converted Dutch roundabouts.117Exhibit 5-17.British crash rates (crashes per million trips) for bicyclists andmotorcyclists at roundabouts and signalized intersections.120Exhibit 5-18.A comparison of crashes between signalized a
7、nd roundaboutintersections in 1998 in 15 French towns.120CONTENTS103Roundabouts: An Informational Guide 5: SafetyChapter 5SafetyRoundabouts may improve the safety of intersections by eliminating or altering con- flict types, by reducing speed differentials at intersections, and by forcing drivers to
8、 decrease speeds as they proceed into and through the intersection. Though round- about crash records in the United States are limited, the experiences of other coun- tries can be used to help design roundabouts in this country. Understanding the sensitivity of geometric element parameters, along wi
9、th the crash experience, will assist the designer in optimizing the safety of all vehicle occupants, pedestrians, and bicyclists.5.1 IntroductionMany studies have found that one of the benefits of roundabout installation is the improvement in overall safety performance. Several studies in the U.S.,
10、Europe, and Australia have found that roundabouts perform better in terms of safety than other intersection forms (1, 2, 3, 4). In particular, single-lane roundabouts have been found to perform better than two-way stop-controlled (TWSC) intersections in the U.S. (5). Although the frequency of report
11、ed crashes is not always lower at roundabouts, the reduced injury rates are usually reported (6). Safety is better at small and medium capacity roundabouts than at large or multilane roundabouts (1, 7). While overall crash frequencies have been reduced, the crash reductions are most pronounced for m
12、otor vehicles, less pronounced for pedestrians, and equivocal for bicyclists, de- pending on the study and bicycle design treatments (4, 6, 7). Crash statistics for various user groups are reported in Section 5.3.The reasons for the increased safety level at roundabouts are:Roundabouts have fewer co
13、nflict points in comparison to conventional intersec- tions. The potential for hazardous conflicts, such as right angle and left turn head-on crashes is eliminated with roundabout use. Single-lane approach round- abouts produce greater safety benefits than multilane approaches because of fewer poten
14、tial conflicts between road users, and because pedestrian crossing distances are short.Low absolute speeds associated with roundabouts allow drivers more time to react to potential conflicts, also helping to improve the safety performance of roundabouts.Since most road users travel at similar speeds
15、 through roundabouts, i.e., have low relative speeds, crash severity can be reduced compared to some tradition- ally controlled intersections.Pedestrians need only cross one direction of traffic at a time at each approach as they traverse roundabouts, as compared with unsignalized intersections. The
16、 conflict locations between vehicles and pedestrians are generally not affected by the presence of a roundabout, although conflicting vehicles come from a more defined path at roundabouts (and thus pedestrians have fewer places to check for conflicting vehicles). In addition, the speeds of motorists entering and exiting a roundabout are reduced with good design. As with other crossingsRoundabouts may improve intersection safety by:Eliminating or altering conflictsDecreasing speeds in
