Bicycle Railing Height Report - AASHTO - Subcommittee on Design

DETERMINATION OF APPROPRIATE RAILING HEIGHTS FOR BICYCLISTS
NCHRP 20-7 (168)
Additional Recommendations
The following issues are recommended for further consideration or study.
Criteria for determining when <strong>Bicycle</strong> <strong>Railing</strong> should be specified
During the course of the research and outreach effort, it became clear that one of the
major concerns of transportation planners and designers is the lack of guidance relative to
specifying bicycle railing on bridges that do not have designated bicycle facilities, but
that experience bicycle traffic. This issue and the current guidance from <strong>AASHTO</strong>
documents is discussed in Chapter 3.
Although this issue was not part of the problem statement or project objective, and the
survey was not designed to solicit information or preferences regarding the need for
bicycle railing, numerous questions and comments were received relative to the need for
guidance in this area. Indeed, three of the six crashes that occurred on roadway bridges
involved vehicular railing that was less than 1.4 m (54 inch) bicycle railing. It appears
that criteria addressing the need for bicycle railing on bridges may have a greater impact
on the safety of bicyclists than the critical height of bicycle railing.
Some of the questions that have been raised that will need further analysis are:
• What is considered “occasional” bicycle traffic?
• How much “shy” distance from a vehicular barrier is necessary for a bicyclist to
safely travel on a bridge?
• What bridge length or duration of exposure is acceptable for bicycle traffic next to
vehicular railing?
• Should geometric conditions such as grade or environmental conditions such as
crosswinds be considered?
<strong>Railing</strong> spacing on a 1.2 meter (48 inch) high combination bicycle railing
The <strong>AASHTO</strong> Standard Specifications for Highway Bridges limits the spacing between
rails on combination pedestrian and bicycle railings. The documents states “Within a
band bordered by the bikeway surface and a line 27 inches above it, all elements of the
railing assembly shall be spaced such that a 6-inch sphere will not pass through any
opening. Within a band bordered by lines 27 and 54-inches, elements shall be spaced
such that an 8-inch sphere will not pass through any opening.”
The spacing appears to be very conservative. In fact, the 1989 <strong>AASHTO</strong> Guide
Specification for Bridge <strong>Railing</strong> specifies “a maximum clear spacing of 15 inches.”
If the top rail of a 1.1 m (42 inch) combination pedestrian railing was raised an additional
150 mm (6 inches) to a 1.2 (48 inch) height combination bicycle railing, the need for an
additional rail would not be necessary. The cost of a combination bicycle railing would
be substantially reduced with the elimination of the additional rail that a 1.4 m (54 inch)
high railing currently requires. The opening between the two top rails would be 360 mm
(14 inches) if the top rail was raised.
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