Narrower Lanes, Safer Streets

Of all street design elements, no other has evoked as much bafflement, incredulity and conjecture as the safer range of travel lane width. Traditional traffic engineers argue wider lanes are safer. Supporters of the livable street concept passionately promote the safety benefits of a relatively narrower lane width. Recent claims are emerging in favour of the livable street approach. However, neither side has yet produced any empirical evidence that links crash frequency or severity to lane width. This paper attempts to address this disquieting quandary. Extensive literature review, both academic and project reports or articles, has been conducted to examine recent claims and outline an emerging scientific perspective, and to provide an important logical platform for this research. In order to examine a relationship between lane width and crash rates, this study utilized two existing crash databases from Tokyo and Toronto, originally collected as part of greater effort to investigate the occurrence mechanism for vehicle-to-vehicle side-impact crashes at signalized intersections. Five novel but identical evidences are discovered for both cities. Both narrow (less than 2.8m) and wide (over 3.1~3.2m) lanes have proven to increase crash risks with equal magnitude. Safety benefits bottom out around 3.1m (for Tokyo) and 3.2m (for Toronto). Beyond the “safety valley curve”, wider lanes (wider than 3.3m) adversely affect overall side-impact collisions. Secondly, among the types of crashes, right-turn crashes are relatively sensitive to lane width, while the safer range of lane width is relatively narrower for right-angle and left-turn crashes. Thirdly, the lateral displacement of driving maneuvers or oscillations stays within a narrow range (0.2m from bottom of safety curve), implying that humans display a surprisingly narrow “safety comfort zone” while trying to achieve a dynamic equilibrium status within the travel lane width. Fourthly, the capacity of narrower lanes is higher. No difference on safety and large vehicle carrying capacity is observed between narrower and wider lanes. Pedestrian volume declines as lanes widen, and intersections with narrower lanes provide the highest capacity for bicycles. Finally, wider lanes (over 3.3~3.4m), the predominant practice of Toronto regions, are associated with 33% higher impact speed rates and higher crash rates, despite higher traffic volumes and one-sixth the population than that of Tokyo. Given that the empirical evidence favours ‘narrower is safer’, the ‘wider is safer’ approach based on personal or intuitional opinion should be discarded once and for all. The findings acknowledge human behavior is impacted by the street environment, and narrower lanes in urban areas result in less aggressive driving and more ability to slow or stop a vehicle over a short distance to avoid collision. Designers of streets can utilize the “unused space” to provide an enhanced public realm, including cycling facilities and wider sidewalks, or to save money on the asphalt not used by motorists.

Journal of Transportation Safety & Security, 2017

As agencies consider strategies for meeting the livability goals (e.g. public health, mobility, and access) of communities, they often repurpose the existing right-of-way of arterials to meet traffic operation or safety goals. Agencies need more definitive guidance on when this repurposing of existing right-of-way can be done without negatively impacting safety. Researchers around the world have considered the safety efficacy of lane width but none define lane width design recommendations of urban arterials. This study uses treed regression analysis on crash data collected from four cities of Nebraska to develop predictive models for identifying the Crash Modification Factors of different lane widths. The analysis from five treed regression models indicates that narrower lanes increase the likelihood and the frequency of both injury and noninjury crashes on high-volume segments; however more specifically, the results also show that narrower lane widths can be adopted for segments with lower volumes, a sufficient number of through lanes, and lower speed limits without degrading safety. Based on these Crash Modification Factors, the research team creates design recommendations for arterial lane widths using combinations of speed limit, average annual daily traffic per lane, and number of through lanes.

terms lane width, roadway width, carriageway or pavement width will be used 1 interchangeably. Earlier drafts of this papers were prepared in the course of a project for UMA 2 Engineering (for the new Canadian Geometric Design Guide) and for DELCAN (in ORSAM 98). "On rural two-lane roads capacities of 10 and 11-fr lanes, expressed as a percentage of 3 12-ft lane capacity are 77 and 88 percent, respectively.r four lane undivided highways these percentages are 89 and 95 . . ." (Green book, 1984, p. 360). Capacity is the reciprocal value of the average minimum headway. Thus, with wider lanes drivers choose shorter headways. 1.1 C:\work\PROJECTS\HSIS\IHSDM-Multilane\Literature Reviews\1. Lane width\lane width.wpd This is an unedited draft reflecting my personal opinions. Ezra Hauer Lane Width and Safety. 1 E. Hauer. Draft , March 7, 2000. 2 1. Introduction. The link between lane width and safety is woven of two principal strands. First, the wider the lanes the larger will be t...

Transportation Research Record: Journal of the Transportation Research Board, 2009

1981

A study to determine the effect of lane and shoulder widths on accident benefits for rural, two-lane roads and to determine the expected cost-effectiveness of lane and shoulder widening is described. Information concerning geometrics, accidents, and traffic volumes was obtained for more than 25,000 km (15,000 miles) of roads. Run-off-road and opposite-direction accidents were the only accident types found to be associated with narrow lanes and shoulders. Wide lanes had accident rates 10-39 percent lower than those for narrow lanes. Wide shoulders (up to 2.7-m (9-ft) width) were associated with the lower accident rates. Criteria based on a cost-effectiveness approach for selecting highway sections for widening are presented. (Authors)

2004

Contents of the project: Human errors play a vital role in road crashes. This report deals with the prevention of human errors by proper road planning, road design and improving existing roads. Road safety considerations must play an explicit role in decision making in all three areas.

Journal of Transportation Safety & Security, 2017

This paper examined the relationship between travel speeds and crashes on two-lane highways, accounting for traffic exposure and road infrastructure characteristics. The study's database included 179 road sections in Israel, which included free-flow travel speeds, three-year injury crash data, traffic volumes and road infrastructure characteristics. Preliminary analyses of in-data correlations supported the selection of appropriate speed and infrastructure indicators. Homogeneous groups of road sections were identified according to their characteristics. Negative binomial statistical models were fitted to injury crash counts for day-and night-hours, using speed indicators, section length, traffic volume and the homogeneous road groups, which reflected various road design conditions. The models demonstrated a positive relation between mean speeds and crashes, while controlling for traffic and road characteristics. The expected crash change following higher travel speeds was more substantial for night hours. In line with previous research, section length, traffic volume and worse road design were positively related to crashes.

2009

Research has shown that road lane width impacts on driver behaviour. This literature review provides guidelines to assist in the design, construction and retrofitting of urban roads to accommodate road users' safety requirements. It focuses on the impacts of lane widths on cyclists and motor vehicle safety behaviour. The literature review commenced with a search of library databases. Peer reviewed articles and road authority (local, state and national) reports were reviewed. The majority of studies investigating the effects of lane width on driver behaviour were simulator based, while research into cycling safety involved data collected from actual traffic environments. Results show that marked road lane width influences perceived task difficulty, risk perception and possibly speed choice. The positioning of cyclists in traffic lanes is influenced by the presence of on-road cycling facilities and the total roadway width. The lateral displacement between bicycle and vehicle is smallest when a bicycle facility is present. Lower, or reduced, vehicle speeds play a significant role in improving bicyclist and pedestrian safety. It is also shown that if road lane widths in urban areas were reduced, to a functional width that was less than the current guidelines of 3.5m, it could result in a safer road environment for all road users.

An analysis was performed to quantify the accident effects of lane and shoulder widths on rural roads carrying fewer than 2,000 vehicles per day. The primary data base used in the research contained accident and roadway characteristic information for more than 6600 km (4,100 mi) of two-lane roadway sections in seven states. Independent data bases from three states (Minnesota, Illinois, and North Carolina) for roadways totaling more than 86 000 km (54,000 mi) were selected to validate the accident relationships found in the primary data base. Analysis of covariance was used to quantify accident relationships on these low-volume roads. Single-vehicle and opposite-direction accidents were classified as related accidents because the accident rates for these two types were found to be related to differences in lane and shoulder widths. The rate of related accidents was also affected by roadside hazard, roadway terrain, the number of driveways per mile, and state differences. No differenc...

2009

The Federal Highway Administration (FHWA) organized a pooled fund study of 26 States to evaluate low-cost safety strategies as part of its strategic highway safety effort. The goal of this study is to evaluate the safety effectiveness of various lane-shoulder width configurations for fixed total paved widths as a countermeasure for roadway departure crashes. Where possible, crash modification factors (CMF) are provided for specific lane-shoulder configurations. The cost of this treatment is essentially zero because it involves only the location of pavement markings. A matched case-control analysis was applied to geometric, traffic, and crash data for road segments in Pennsylvania and Washington. In general, wider pavement widths 9.75-10.97 m (32-36 ft) are associated with fewer crashes than narrower paved widths 7.92-9.14 m (26-30 ft). For specific lane-shoulder configurations, there is a general safety benefit associated with wider lanes and narrower shoulders for a fixed pavement width. For 7.92-to 9.75-m (26-to 32-ft) total paved widths, a 3.66-m (12-ft) lane provides the optimal safety benefit; the CMF ranges from 0.94 to 0.97, indicating a 3-6 percent crash reduction for 3.66-m (12-ft) lanes compared with 3.05-m (10-ft) lanes. For a 10.36-m (34-ft) total paved width, 3.35-m (11-ft) lanes provide the optimal safety benefit; CMF was 0.78 compared with the 3.05-m (10-ft) baseline. For a 10.97-m (36-ft) total paved width, both 3.35-m and 3.66-m (11-ft and 12-ft) lanes provide the optimal safety benefit; CMF was 0.95 compared with the 3.05-m (10-ft) baseline. Based on the estimated safety effectiveness of this strategy, specific laneshoulder configurations have the potential to reduce crashes cost effectively on rural, two-lane, undivided roads. However, limited sample sizes make it difficult to identify statistically significant differences between certain lane-shoulder configurations within a total paved width.