Sidepath Suitability Score

Ed Barsotti, League of Illinois Bicyclists, April 3, 2001

The following algorithm rates the suitability of a sidewalk or sidepath as a bicycle facility. (A sidepath is a trail parallel to, but separated from, a roadway). The algorithm can be used to:

• Rate existing sidepaths
• Determine whether a new sidepath would be an appropriate option for accommodating bikes
• Suggest safety improvements for existing or planned sidepaths

At present, no such nationally-accepted suitability index exists. The AASHTO Guide for the Development of Bicycle Facilities describes some of the problems encountered when using sidewalks or sidepaths as bicycle facilities. I have attempted to combine these and other factors into a quantified suitability score. No field testing, statistical analysis, or calibration has been done - the algorithm is only my estimation of the relative importance of key terms. It was developed for the Non-Motorized Transportation Plan of North Aurora, Illinois.

The factors considered are: intersection traffic, continuity, curb cuts, pedestrian use, crosswalks, and path/road separation at intersections. Assumed is that bicyclists will travel in both directions on the sidepaths.

1. Intersection Traffic Score.
The volume and speed of traffic - especially turning traffic - directly affect the risk of collision. Determine the intersection traffic score X from the following:
X = [R+(2*A)+(4*B)] / M * [Spd*Vol];
Where:
R = Number of residential intersections (driveways) on the segment,
A = Number of minor commercial intersections and streets (<1000 ADT),
B = Number of major commercial intersections and streets (>1000 ADT),
M = Length of segment in miles
Spd = Speed limit factor, for the parallel street: 30 and under = 1, 35-40 = 2, 45 and over = 3.
Vol = Traffic volume factor, parallel street: <2,000 = 1; 2,000-10,000 = 2; >10,000 = 3.

X	Points
0	0
1-40	1
41-80	2
81-120	3
121-160	4
161-200	5
201-240	6
>240	7

2. Continuity.
Discontinuities (major gaps, or sidepath ends) may force cyclists to ride through grass, etc., and enter the roadway awkwardly. Often cyclists will avoid sidepaths with these gaps. Add 4 points if major discontinuities exist.

3. Curb cuts.
Uncut curbs compromise cyclist movement and attention at intersections. Add 3 points if any intersections are lacking curb cuts.

4. Pedestrian use.
Sidewalks and sidepaths are used by both bicyclists and pedestrians. Insufficient width increases user conflict. (However, extra width encourages higher cyclist speeds - which becomes a problem at incorrectly-designed intersections.) Add points according to the following chart:

Low (rare) ped use		Medium (sometimes) ped use		High (often) ped use
<= 5'	1 point	<= 5'	2 points	<= 5'	4 points;
> 5'	0 points	6-7'	1 point	6-7'	2 points
		>= 8'	0 points	>= 8'	1 point;

5. Crosswalks.
Visible crosswalks can help make motorists more aware of non-motorized traffic. Sometimes 2 parallel painted stripes are sufficient. At busier intersections, ladder crosswalks and other techniques enhance visibility. Add 2 points if there are no crosswalks. Add 1 point if there are some crosswalk markings, but more visibility is warranted for that intersection type. Add 0 points for appropriately marked crossings. Take the average crossing for the segment.

6. Intersection sidepath/road separation.
AASHTO recommends that sidepaths be brought closer to the parallel road at intersections, so motorists more easily see and consider bicyclists during their approaches. The vehicular stop line should be in back of the sidepath crossing - cyclists must not weave through stopped traffic when crossing. Add 5 points if the crossing goes through stopped traffic. Add 3 points if the crossing is not brought "close enough" to the parallel road. Add 1 point when the crossing is brought close to the road. (Paved shoulders and bike lane crossings - 0 points.) Again, take the average crossing for the segment.

Add together all the points for the sidepath suitability score. Ranges of suitability are: