Characteristics of Emerging Road and Trail Users and Their Safety

Design Speed

The selected design speed of a facility affects many aspects of geometric design. Consequently, it can significantly impact the cost, constructability, and operational safety of a project. The AASHTO Guide for the Development of Bicycle Facilities (p. 36) specifies 30 km/h (20 mi/h) as the minimum design speed that should be used on shared use paths (figure 47).⁽²⁾ It goes on to provide modifiers for grades and strong prevailing winds.

Figure 47. AASHTO's design bicyclist travels at 30 km/h (20 mi/h).
(Photo by Dan Burden.)

Of the bicyclist participants in this research project, only four, or 1 percent, exceeded the suggested 30-km/h (20-mi/h) design speed. The 85^th percentile speed for bicyclists was 22 km/h (14 mi/h). This suggests that the 30-km/h (20-mi/h) design speed may be conservative; however, further research is needed.

Recumbent bicyclists had the highest observed 85th percentile speeds, 29 km/h (18 mi/h). This may suggest that they may be the appropriate user upon which to set a minimum design speed. However, as discussed in the following sections, the additional design characteristics of the various users need to be evaluated before such a conclusion can be drawn.

At the other extreme, hand cyclists appear to have the lowest 15^th percentile speed, 8 km/h (5 mi/h), of those users who would be expected to operate in the street. Strollers had the lowest 15^th percentile speed, 4 km/h (3 mi/h) (table 12).

^2. American Association of State Highway and Transportation Officials. Guide for the Development of Bicycle Facilities. American Association of State Highway and Transportation Officials, Washington, DC, 1999.