Recommended Bicycle Lane Widths for Various Roadway Characteristics (2014)

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1 S u m m a r y The 2012 edition of the American Association of State Highway and Transportation Offi- cials’ Guide for the Development of Bicycle Facilities (AASHTO, 2012), often referred to as the Bike Guide, defines a bicycle lane as “a portion of a roadway that has been designated for pref- erential or exclusive use by bicyclists by pavement markings and, if used, signs. It is intended for one-way travel, usually in the same direction as the adjacent traffic lane, unless designed as a contra-flow lane.” The AASHTO Bike Guide provides general guidance on appropriate bicycle lane widths. The Bike Guide states that, in most situations, the recommended width for bike lanes is 5 ft, but in some circumstances, wider bicycle lane widths may be desirable, while in other cases a 4-ft-wide bike lane can be used. The guidelines for bicycle lane widths provide only general guidance on how bicycle lane widths should vary based on the condi- tions of the roadway. There is a need to conduct scientifically based research to develop more specific guidance on bicycle lane widths for various roadway conditions. The objective of this research was to develop recommendations for bicycle lane widths for various roadway and traffic characteristics. The focus was on developing design guidance for bicycle lane widths for roadways in urban and suburban areas. An observational field study was conducted to evaluate the allocation of roadway width on both bicyclists’ and motorists’ lateral positioning, taking into consideration various roadway and traffic characteristics. The general methodology of the field study involved installing temporary lane line mark- ings to delineate bicycle lanes of varying widths at midblock locations and observing the behavior of bicyclists and motorists. The final database from the observational field study included data on 4,965 bicyclists, 3,163 passing vehicles, and 994 parked vehicles. The primary roadway and traffic characteristics that factored most into selecting sites for inclusion in the observational field study were: • Bicycle volume, • Traffic volume, • Vehicle mix (i.e., percent trucks), • Lane width and/or total roadway width, and • Presence/absence of on-street parking. Given the site characteristics and the study scenarios, the ranges in the primary roadway and traffic characteristics analyzed in this research are: • Bike lane width: 3.5 to 6 ft, • Parking lane width: 7 to 9 ft, • Travel lane width: 10 to 18 ft, • Presence/absence of buffer space,

2• Traffic volume: 14,800 to 29,000 vehicles per day (vpd), and • Percent trucks: 2% to 20%. Posted speed limit and grade were additional characteristics of interest identified for evaluation in this research; however; all of the sites included in the observational field study had a posted speed limit of 30 mph, and all sites were on a level grade. The effect of grade on bicyclist behavior was evaluated through a supplemental grade study. The conclusions of the research are as follows and should be considered within the context of the research. In particular, the conclusions are most applicable to urban and suburban roadways with level grades and a posted speed limit of 30 mph and should be used cautiously for the design of roadways with motor vehicle speeds outside of the range of 25 to 35 mph and, in particular, for higher-speed roadways. General Conclusions 1. A buffered bike lane provides distinct advantages over simply providing a wider bike lane. 2. Narrowing the width of a bicycle lane reduces the variability of the bicyclists’ lateral posi- tions; however, this impact is relatively minor, at least for the bicycle lane widths evaluated in this research. 3. As traffic volume increases, bicyclists move away from vehicles in the travel lane and posi- tion themselves closer to parked vehicles or the curb. 4. As truck percentage within the vehicle mix increases, bicyclists move away from vehicles in the travel lane and position themselves closer to parked vehicles or the curb. 5. For streets with on-street parking and where the parking lane width is between 7 and 9 ft and the bike lane width is between 4 and 6 ft, the effective bike lane will likely be less than the physical width of a typical adult bicyclist, and the majority of bicyclists will position themselves outside of the effective bike lane. 6. For streets without on-street parking, as long as the adjacent travel lane is at least 10-ft wide and the bike lane is 4 to 5 ft in width, most bicyclists will position themselves in the effective bike lane, and the effective bike lane will be equivalent to the width of the marked bike lane. Design Guidance 1. Travel lanes between 10 and 12 ft in width are appropriate for streets with a bicycle lane. 2. At sites with travel lane widths between 16 and 18 ft on streets without on-street park- ing, marking a bicycle lane provides no distinct advantages for the lateral positioning of bicyclists and motorists. While this statement is true with respect to the issues addressed in this particular study, there are other reasons why bike lanes on streets with 16- to 18-ft lanes would be desirable. These include using the bike lane to narrow the travel lane to provide a traffic calming measure; encouraging bicyclists to travel in the correct direc- tion on the street; getting bicyclists off of adjacent sidewalks, where they are generally less safe (Wachtel and Lewiston, 1994); and using the bike lane as a link to a larger bikeway network. 3. In most situations where a bicycle lane is adjacent to on-street parking, the suggested width for the parking lane is 8 ft. An 8-ft parking lane provides sufficient space for a large percentage of vehicles to park within the limits of the parking lane, and it is narrow enough that it allows more of the roadway cross section to be designated for bicyclists in the bicycle lane and motor vehicles in the travel lanes. This is consistent with current recommendations in the AASHTO Bike Guide.

3 4. The AASHTO Bike Guide states that under most circumstances, the recommended width for bike lanes is 5 ft. The guide also states that under certain conditions, wider bicycle lanes may be desirable. In particular, the guide states that when adjacent to a narrow parking lane (7 ft) with high turnover, a wider bicycle lane (6 to 7 ft) provides more operating space for bicyclists to ride outside of the door zone of parked vehicles. Based on the data collected in this study, a 6-ft bicycle lane does not provide additional benefits to bicyclists compared to a 5-ft bicycle lane. Most bicyclists will still position themselves within the open door zone of parked vehicles whether in a 6-ft bicycle lane or a 5-ft bicycle lane. A 7-ft bicycle lane may offer distinct advantages for bicyclists compared to bicycle lane widths of 5 and 6 ft; however, data for 7-ft bike lanes were not investigated in this research. Where space permits, the data suggest that installing a narrower bicycle lane with a parking-side buffer provides distinct advantages over a wider bike lane with no buffer. 5. For parking lanes that are 7- to 9-ft wide, assuming the 95th-percentile parked vehicle displacement and an open door width of 45 in., the open door zone width of parked vehicles extends approximately 11 ft from the curb. Therefore, the design of the bike lane should encourage bicyclists to ride outside of this door zone area and account for the width of the bicyclist. Section 5 of this report provides more detailed design guidance related to bicycle lane widths, taking into account a range of roadway and traffic characteristics, including parking lane width, travel lane width, traffic volume, vehicle mix, and grade.