Embedded Files
American Association of State Highway and Transportation Officials (AASHTO)
Guide for the Development of Bicycle Facilities, 4th Ed. (2012)
by the American Association of State Highway and Transportation Officials (AASHTO) [PDF]
Minimum operating width of a bicycle (p. 52)
Critical physical dimensions for upright adult bicyclists are shown in Figure 3-1. The minimum operating width of 4 ft (1.2 m), sufficient to accommodate forward movement by most bicyclists, is greater than the physical width momentarily occupied by a rider because of natural side-to-side movement that varies with speed, wind, and bicyclist proficiency. Additional operating width may be needed in some situations, such as on steep grades, and the figure does not include shy distances from parallel objects such as railings, tunnel walls, curbs, or parked cars. In some situations where speed differentials between bicyclists and other road users are relatively small, bicyclists may accept smaller shy distances. However this should not be used to justify designs that are narrower than recommended minimums.
Bicyclists’ Lateral Position on the Roadway (p. 56)
Bicyclists’ Lateral Position on the Roadway Is Determined by Speed and Usable Width
Bicyclists ride as far right as practical, which on a typical roadway means that the bicyclist rides in (or near) the right tire track. A bicyclist traveling at the same speed as other traffic, or in a travel lane too narrow for a motor vehicle to safely pass without encroaching into the adjacent lane, travels in the center of the lane (often referred to as “taking the lane”). The primary reason for taking the lane is to encourage overtaking traffic to make a full lane change instead of squeezing past the bicyclist in the same lane. The Uniform Vehicle Code and most State codes support bicyclists’ right to take the lane, if necessary. Most vehicle codes also allow exceptions to the rightmost position on the road requirement for reasons such as avoiding hazards, passing other bicyclists and preparing for and making left turns. Slower bicyclists travel to the right of faster bicyclists (and other vehicles). Like other vehicles, emergency stops made by bicyclists must occur at the rightmost position on the road.
4.3.1 Shared Lanes on Major Roadways (Wide Curb/Outside Lanes)
Lane widths of 13 ft (4.0 m) or less make it likely that most motor vehicles will encroach at least part way into the next lane to pass a bicyclist with an adequate and comfortable clearance (usually 3 ft [0.9 m] or more depending on the speed of the passing vehicle). Lane widths that are 14 ft (4.3 m) or greater allow motorists to pass bicyclists without encroaching into the adjacent lane. The usable lane width is normally measured from the center of the edge line to the center of the traffic lane line, or from the longitudinal joint of the gutter pan to the center of the lane line. The gutter should not be included in the measurement as usable width, as bicyclists will typically ride well to the left of the joint.
On sections of roadway where bicyclists may need more maneuvering space, the outside lane may be marked at 15 ft (4.6 m) wide. This width may be appropriate on sections with steep grades or on sections where drainage grates, raised delineators, or on-street parking effectively reduces the usable width. However, lane widths in extremely congested areas that continuously exceed 16 ft (4.9 m) may encourage the undesirable operation of two motor vehicles side by side. The provision of wide outside lanes should also be weighed against the likelihood that motorists will travel faster in them and that heavy vehicles (where present) will prefer them to inside lanes, resulting in decreased level of service for bicyclists and pedestrians. When sufficient width is available to provide bike lanes or paved shoulders, they are the preferred facilities on major roadways. Roadways with shared lanes narrower than 14 ft (4.3 m) may still be designated for bicycles with bicycle guide signs and/or shared-lane markings, per the guidance in this chapter.
Shoulders (p. 69)
For any given roadway, the determination of the appropriate shoulder width should be based on the roadway’s context and conditions in adjacent lanes. On uncurbed cross sections with no vertical obstructions immediately adjacent to the roadway, paved shoulders should be at least 4 ft (1.2 m) wide to accommodate bicycle travel. Shoulder width of at least 5 ft (1.5 m) is recommended from the face of a guardrail, curb, or other roadside barrier to provide additional operating width, as bicyclists generally shy away from a vertical face. It is desirable to increase the width of shoulders where higher bicycle usage is expected. Additional shoulder width is also desirable if motor vehicle speeds exceed 50 mph (80 km/h); if use by heavy trucks, buses, or recreational vehicles is considerable; or if static obstructions exist at the right side of the roadway. The Bicycle LOS model may be used to determine the appropriate shoulder width (see Chapter 2 on “Bicycle Planning”).
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