The Intermodal Surface Transportation Efficiency Act (ISTEA) places increased importance on the use of the bicycle as a viable transportation mode, and calls on each state Department of Transportation to encourage its use. AASHTO's Guide for the Development of Bicycle Facilities is the basic reference for bicycle facility designers. It has been adopted, in part or in its entirety, by many state and local governments. The AASHTO bicycle guidelines state "all new highways, except those where bicyclists will be legally prohibited, should be designed and constructed under the assumption that they will be used by bicyclists."
On existing multi-lane arterials and collectors with relatively high motor vehicle volumes and/or significant truck/bus traffic, a right (curb) lane wider than 12 feet is desirable to better accommodate both bicyclists and motor vehicles in the same travel lane. AASHTO and the National Advisory Committee on Uniform Traffic Control Devices suggest reducing the inside vehicle lanes from 12 feet to 11 feet for the purpose of widening the right-hand lane for bicycle use. The AASHTO bicycle guidelines recommend a "usable" curb lane width of 14 feet on road segments where parking is not permitted in the curb lane. Usable width generally cannot be measured from curb face to lane stripe, because adjustments must be made for drainage grates (even the "bicycle safe" ones) and longitudinal joints between pavement and gutter sections. For instance, on those road segments where no parking is allowed but drainage grates and the longitudinal joints are located 18 inches from the curb face, the travel lane (from joint line to lane stripe) should be 14 feet in width, reflecting the unsuitability of bicycle riding on the outside 18 inches of the roadway.
If parking is permitted in the curb lane, then the minimum width of the curb lane, from curb face to through travel lane is 14 feet, with 15 feet being the desirable width. In this design situation, the lane width is measured from the curb face, since parked motor vehicles can occupy the curb flag (gutter section). Conversely, when bicycles travel directly adjacent to a curb, they cannot safely operate in the gutter section. Wide curb lanes are not striped or generally promoted as "bicycle routes", but are often all that is needed to accommodate bicycle travel. An example of a 151/2-foot curb lane is shown below.
Bicycle lanes are constructed when it is desirable to delineate available road space for preferential use by bicyclists or motorists and to provide for more predictable movements by each. Bicycle lane markings can increase a bicyclist's confidence that motorists will not stray into his/her path of travel. Likewise, passing motorists are less likely to swerve to the left out of their lane to avoid bicyclists on their right. Bike lanes are generally established on urban arterials and sometimes on urban collector streets. Bicycle lanes are delineated by painted lane markings. They should always be one-way facilities and carry traffic in the same direction as adjacent motor vehicle traffic. Two-way bicycle lanes on one side of the roadway are unacceptable because they promote riding against the flow of motor vehicle traffic. Wrong-way riding is a major cause of bicycle accidents. Bicycle lanes on one-way streets should be on the right of the street, except in areas where a bicycle lane on the left will decrease the number of conflicts (e.g., those caused by heavy bus traffic).