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.