Bicycle Railing Height Report - AASHTO - Subcommittee on Design

DETERMINATION OF APPROPRIATE RAILING HEIGHTS FOR BICYCLISTS
NCHRP 20-7 (168)
Table 3 - Eye Level <strong>Height</strong> and Associated Cone of Vision Angle
Person Avg. Eye
Level
<strong>Height</strong>
(in.)
Difference
from 42” rail
(in.)
Cone of
Vision
Angle with
42” rail
(degree)
Difference
from 54” rail
(in.)
Cone of
Vision
Angle with
54” rail
(degree)
Adult Male 65.4 23.4 33˚ 11.4 18˚
Adult Female 61.5 19.5 28˚ 7.5 11˚
Child – 12 yrs. 54.5 12.5 19˚ 0.5 0.8˚
The Effect of <strong>Railing</strong> Transparency on the View
Another consideration is the visual transparency of the railing. The structure of the posts
and rails on a combination traffic and bicycle railing is much heavier than a bicycle
railing due to the vehicle design loadings. The Standard Specifications for Highway
Bridges specifies that all assembly elements of railings 27 inches above the bikeway must
be spaced such that a six-inch sphere will not pass through any opening. Additionally, all
assembly elements of railings between 27 and 54 inches in height must be spaced such
that an 8-inch sphere will not pass through any opening. However, the design of these
openings is often reduced by state design guidelines to prevent large objects from passing
through the barrier. For example, for railings designed for bicyclists or pedestrians,
CalTrans requires bridge elements to be spaced such that a four-inch sphere will not pass
through any opening between the road surface and to 27 inches above it. For subsequent
heights, the spacing must prevent an eight-inch sphere from passing through the
elements. 12 These more restrictive specifications create a greater visual obstruction to the
view beyond the railing.
12
California Department of Transportation, “Bridge Design Specifications,” April, 2000, p. 2-4.
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