Bicycle Railing Height Report - AASHTO - Subcommittee on Design

DETERMINATION OF APPROPRIATE RAILING HEIGHTS FOR BICYCLISTS
NCHRP 20-7 (168)
Acrophobia
The lack of empirical evidence supporting the need for the higher railing height leads to
the possibility that the feeling of insecurity associated with the lower railing height may
be due to a fear of heights. This disorder is known as acrophobia. In general, phobias
(including acrophobia) affect about 9 to 10% of Americans.
Summary
Perception represents a strong force in an individual’s determination of personal safety
when traveling along a bicycle path adjacent to a steep slope or high drop-off. Despite
the lack of empirical evidence proving that a 1.4-meter (54-inch) railing height provides
added protection, many of the responses from the survey and outreach process indicated
that a 1.1-meter (42-inch) high railing was inadequate, and that the additional height
provides an added sense of security. There appears to be a consensus that an increased
level of comfort is experienced when bicycling across a bridge with a 1.4-meter (54-inch)
high railing.
Views and Aesthetics
The issue that appears to have had the greatest influence on lowering the recommended
railing height from 1.4 meters (54 inches) to 1.1 meters (42 inches) is aesthetics. Most of
the relevant survey responses and comments referred to the general term of “aesthetics”
as the reason for preferring a 1.1-meter (42-inch) height railing. Some responses and
comments specifically identify a desire to avoid obstructions to the view.
<strong>Railing</strong> Aesthetics
A number of documents related to bridge aesthetics were reviewed to determine aesthetic
attributes or criteria that should be considered in the design of a railing. Most of the
reviewed documents discuss the design attributes of a bridge, and outline how the
attributes are seen in the context of the surrounding landscape. Typical design attributes
of a bridge that relate to form and aesthetics include proportion, symmetry, order and
rhythm, contrast and harmony, detail, simplicity, and unity of design. The specific bridge
components that are viewed in the context of the surrounding landscape are the piers, side
fascia, abutments, wing walls, and other fixtures, including railings or treatments on the
side of the bridge.
Based on the available guidance on bridge and structure aesthetics, it is difficult to
determine any general suggestions, principles, or guidelines regarding the size, scale, or
form that would render a railing system aesthetically objectionable. Using conventional
wisdom, bridge designers tend to design a shallow bridge section that would be visually
unobtrusive, and maximize the vertical clearance. A higher bridge railing could appear
disproportionate with the thin section of a bridge. However, the visual quality or beauty
of a railing system would have to be judged based on its physical setting.
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