Fig 1.
Geometry of lawfully passing a bicyclist.
Depiction of two common US motor vehicles (typical sedan on the left, pickup truck/sport utility vehicle on the right), 0.91m (3ft) minimum lateral passing distance required in most states (red dashed line), and typical 1.22m (4ft) operating space for bicyclists. The resultant total width does not include any “shy distance,” typically 0.46m (1.5ft) that motorists and bicyclists keep away from hazardous objects, between the motor vehicle and the lane marking to its left, or between the bicyclist and the edge of the road.
Fig 2.
Bicycle-related traffic control devices.
From left to right, “Share the Road” (Manual on Uniform Traffic Control Devices W11-1 upper plaque plus W16-1 lower) and “Bicycles May Use Full Lane” (R4-11) signage; Shared Lane Markings (sharrows) are painted on the roadway pavement [21].
Fig 3.
Each tweet included a request that the viewer complete our survey and retweet it and was directed at other Twitter users (the @handles) and Twitter users interested in specific issues (keywords preceded by #).
Fig 4.
This shows the image and statements we used for the two-lane roadway with the Bicycles May Use Full Lane signage treatment. Images for the other three treatments were identical except for signage, which was appropriate for the treatment. The full survey is shown in S1 Methods; images for all four treatments are reproduced in S2 Methods.
Table 1.
Characteristics of our survey respondents.
Fig 5.
Comparison of agreement with four road use statements under three treatments.
Bicycle May Use Full Lane–square; Shared Lane Markings–inverted triangle; Share the Road–yellow diamond; and control (No Sign)–red circle on 2-lane (left column) and 4-lane (right column) roads. In each plot results for the overall sample (n = 1,824) are compared to respondents who bicycle ≤ 16km/week (n = 369), who commute by personal motor vehicle (n = 776), who bicycle > 16km/week (n = 1,455), and who commute by other means (n = 1,048). The y-axis scales vary among statements (rows). For all respondents, significant differences between the Bicycles May Use Full Lane treatment and the control (No sign) are marked using * for p<0.1, ** p<0.05, *** p<0.01; similarly, for the Shared Lane Marking treatment they are marked using +; Share the Road never differed significantly from no signage.
Table 2.
Comparison of agreement with four road use statements by treatment and by two user categories on 2- and 4-lane roads.