Bicycle Railing Height Report - AASHTO - Subcommittee on Design
Bicycle Railing Height Report - AASHTO - Subcommittee on Design
Bicycle Railing Height Report - AASHTO - Subcommittee on Design
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DETERMINATION OF APPROPRIATE RAILING HEIGHTS FOR BICYCLISTS<br />
NCHRP 20-7 (168)<br />
The Effect of <str<strong>on</strong>g>Railing</str<strong>on</strong>g> <str<strong>on</strong>g>Height</str<strong>on</strong>g> <strong>on</strong> the View<br />
The ability to see over a traffic barrier designed for bicyclists appears to be an issue for<br />
motorists in mountainous terrain or where the viewing subject is higher than the horiz<strong>on</strong><br />
line. For the purposes of calculating sight distance, the average height of a vehicle<br />
occupant’s eye is 1,080 mm or 1.1 meters (42 inches), 10 which corresp<strong>on</strong>ds to a 1.1-meter<br />
(42-inch) railing height. Theoretically, a pers<strong>on</strong> in a vehicle would have an uninterrupted<br />
view of objects above the horiz<strong>on</strong> line if the railing height were 1.1 meters (42-inches).<br />
The view would ultimately depend <strong>on</strong> the cross slope of the roadway, the l<strong>on</strong>gitudinal<br />
slope of the roadway, and the vehicle occupant’s c<strong>on</strong>e of visi<strong>on</strong>. The additi<strong>on</strong>al 0.3<br />
meters (12 inches) of a 1.4-meter (54-inch) high railing would likely obscure a vehicle<br />
occupant’s view of the horiz<strong>on</strong>.<br />
The ability to see over a railing al<strong>on</strong>g a bikeway is a functi<strong>on</strong> of the eye level height of<br />
the bicyclist or pedestrian. The average eye level of a bicyclist varies with the type of<br />
bicycle, riding stance, and seat height. For the purposes of illustrating the impact of<br />
railing height <strong>on</strong> the unobstructed view from a bikeway, the average height of<br />
pedestrians, rather than bicyclists, was used for this study. Data for pedestrians is more<br />
readily available and c<strong>on</strong>sistent.<br />
The average standing eye level height is 65.4 inches for an adult male and 61.5 inches for<br />
an adult female. The average eye level height of a 12-year old child is 54.5 inches. 11 As<br />
illustrated in Table 3, the difference in eye height and railing height for a 1.1-meter (42-<br />
inch) high railing is much greater than that for a 1.4-meter (54-inch) high railing. The<br />
lower height can greatly increase the potential for an unobstructed view from a pedestrian<br />
<strong>on</strong> a bikeway.<br />
The measure of the unobstructed view is<br />
determined by an individual’s c<strong>on</strong>e of visi<strong>on</strong><br />
angle. As shown in Figure 11, a 64.5-inch<br />
tall adult male, positi<strong>on</strong>ed three feet from a<br />
1.1-meter (42-inch) railing, has a c<strong>on</strong>e of<br />
visi<strong>on</strong> angle of 33 degrees. C<strong>on</strong>sequently,<br />
the same adult male positi<strong>on</strong>ed before a 1.4-<br />
meter (54-inch) railing has a smaller c<strong>on</strong>e of<br />
visi<strong>on</strong> angle (18 degrees), and therefore,<br />
experiences a greater obstructed view. Table<br />
3 provides the c<strong>on</strong>e of visi<strong>on</strong> angles for an<br />
adult male, adult female, and child positi<strong>on</strong>ed<br />
before a 1.1-meter (42-inch) and 1.4-meter<br />
(54-inch) railing.<br />
Figure 11 - C<strong>on</strong>e of Visi<strong>on</strong> Angle<br />
10<br />
<str<strong>on</strong>g>AASHTO</str<strong>on</strong>g>, “A Policy <strong>on</strong> Geometric <strong>Design</strong> of Highways and Streets,”4 th Ed., 2001, p. 127.<br />
11 Hoke, Jr., John R., American Institute of Architects, Ramsey/Sleeper, “Architectural Graphic<br />
Standards,” 9 th ed., 1994, p. 1.<br />
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