Factors Affecting Vehicle Passing Distance and Encroachments While Overtaking Cyclists

State and local governments are interested in providing safe and comfortable bicycle infrastructure that encourages cycling as a mode of transportation. After Hennepin County, MN, USA acquired C3FT bike-mounted radars, they collaborated with the University of Minnesota on a study of vehicle passing behavior on the county bicycle network. This study used two measures of relative safety: (1) vehicle passing distance (VPD) when overtaking cyclists, and (2) encroachments. Minnesota statute requires a minimum VPD of 3 feet (36 inches) while passing a cyclist. Anything less is an encroachment. This report investigates vehicular encroachment and VPD while overtaking cyclists on different bicycle facilities across seven roadways in Hennepin County.

Literature Review

Municipalities are grappling with building bicycle infrastructure to encourage more cyclists without interfering with traffic flows or exceeding budgets. At the center of this challenge is the need to ensure cyclist safety. In theory, increasing the safety of roads for cyclists should result in greater numbers of cyclists.1

A number of studies have looked at what variables influence vehicle-cyclist interactions, including VPD. Table 1 summarizes seven studies and their significance. Three studies found that VPD decreased when there was an adjacent vehicle. The literature has mixed findings regarding roadway characteristics such as lane width, speed limit, and shoulder width. Three studies in Table 1 find that wider lanes increase VPD. Two studies find speed limit influences VPD but they find opposing effects. In one study vehicle type was significant with trucks having the smallest "comfort zone boundary." 2 The apparel of the cyclist does not appear to affect VPD, but evidence points to the need to look at gender.3 Stipancic et al. found that female cyclists were more likely to be involved in dangerous conflicts at intersections.4

Study Background and Methodology

The entirety of the study can be summarized chronologically with the following steps:

1. Equipment Testing

2. Controlling Cyclist Position

3. Defining a Pass

4. Selecting Roadways

5. Delineation

6. Data Collection

7. Data Analysis

Equipment Testing

Two researchers tested the C3FT bike mounted radar's utility as a tool for study. Figure 1 shows the C3FT radar and GoPro mounted on a bike for testing. The equipment successfully captured VPD, but because the equipment does not record data, researchers needed to watch the GoPro...