DRAFT Comprehensive Transportation Plan Update: 2/23/2018 version

DESIGN SPEED The design speed determines the geometric features of a new or existing multi-use path in the design process. The design speed can

fluctuate depending on the context of the path, the user types expected, the path terrain, and other path characteristics. Table F-3 shows

the horizontal curves recommended for use at various design speeds. Engineering judgement needs to be applied on a case-by-case basis

to determine the most appropriate design speed. In addition, other factors including stopping distance will need to be considered. The

following examples from AASHTO help to illustrate these factors:

Guidelines  According to AASHTO, the typical riding speed varies from 8-to 15-mph for cyclists.

 Multi-use paths anticipated to accommodate a variety of user types or frequent conflicts and constraints must be designed for

lower design speeds than multi-use paths with few conflicts.

 Allow for an 18-mph design speed for relatively flat areas, except on inclines where high speeds can occur.

 Design speed within a maximum downhill terrain condition (6 percent or greater) is 30-mph

 Horizontal curvature in path design can reduce speed

Table F-3. Minimum Radii for Horizontal Curves

DESIGN SPEED (MPH)

MINIMUM RADIUS (FT.)

12 14 16 18 20 25 30

27 36 47 60 74

115 166

CURVE WIDENING

In some circumstances when environmental or physical constraints limit the geometrics, slower design speeds (12 to 16 mph) may be

appropriate and sharper horizontal curves may be used. Figure F-2 (taken from the North Carolina Bicycle Facilities Planning and

Design Guidelines ) provide an example of the maximum widening of 4 feet to a path. The suggested minimum curve widening within the

Town is 2 feet.

Guidelines  Wider paths (12 feet or greater) or curve widenings are recommended to let users navigate the effects of substandard curves.

 Curve widening of 2 to 4 feet must be implemented.

Figure F-2: North Carolina Bicycle Facilities Planning and Design Guidelines Curve Widening Example

STOPPING SIGHT DISTANCE AND MINIMUM VERTICAL CURVE Providing multi-use path users with opportunities to visually see unexpected conditions can be achieved through designing appropriate

stopping sight distances. The AASHTO Guide for the Development of Bicycle and Pedestrian Facilities has been referenced to present

stopping sight distance (SSD) in the figures below. Figure F-3 presents the minimum (SSD) controlled by the ascending grade. Figure F-4

shows the determined stopping sight distance vs. the grade in a descending path. Figure F-5 then shows the minimum SSD that can be

used to determine the minimum crest vertical curve length.

Guideline 

Minimum length of a vertical curve is 3 feet

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