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Road Safety Performance Associated with Improved Traffic Signal Design and Increased Signal Conspicuity

3.0 Background and Early Installations

In 1998, MoT and ICBC initiated a project entitled, Safety Benefits of Improved Signal Backboard Visibility. The purpose of the project was to study the safety performance impacts associated with highly reflective tape on signal head backboards. Standard size backboards were fitted with an additional 75mm reflective border. The objective was to determine if the new signal backboard design resulted in a reduction in traffic accidents at signalized intersections. The new signal backboard design is expected to be effective in reducing rear-end accidents and, to a lesser degree, other miscellaneous intersection accident types.

In September 1998, 3M yellow diamond grade VIP reflective tape was placed on the outer edge of the yellow backboards on the signals heads of six intersections located along McKenzie Avenue Expressway between the Patricia Bay Highway and the Trans Canada Highway in Saanich BC. Figure 1 shows a backboard with tape during the daytime, providing evidence that the tape highlights the border of the backboard. The effect of the tape during nighttime is very pronounced as shown in Figure 2. The tape provides a distinctive frame around the traffic signal display, allowing drivers to more readily locate the signal head among background lighting. There may be a secondary benefit when there is a power failure since the driver will see the backboard without a signal display.

Figure 1. Signal During the Day

photo depicting signal head with reflective backboard,highly visible against daytime background.

Figure 2. Signal During the Night

photo depicting signal head with reflective backboard,highly visible against nighttime background.

The Saanich Police Department collected the accident data for the study, including the requisite data for both the pre-installation and post-installation time periods. The before and after traffic volume data was obtained from the engineering departments from the Municipality of Saanich. The results from a simple before and after safety analysis was undertaken by MoT with the results indicating that the aggregate collision frequency was reduced from the before to the after periods. Although it is known that a simple before and after road safety analysis can be unreliable (and the sample size of treated locations was small), a decision was made to expand the number of intersections to which the treatment was applied. This decision was made based on the encouraging results from the simple before-after results and because of the low cost of the improvements. Hence, MoT in partnership with ICBC began applying the highly reflective tape around signal backboards at a number of intersections on Vancouver Island.

The relative effect of the retro-reflective tape on the backboard is significant. Figure 3 shows an intersection that has two primary signal heads for the through movement. Both signal heads have backboards however only the left-side signal head has retro-reflective tape around the outside of its backboard. The visibility of the right-side signal head (located to the right of the street sign) is difficult to identify from the background lighting. The figure clearly illustrates the difference in visibility between the two signal displays.

Figure 3. Traffic Signal Framed with Highly Reflective

photo depicting two signal heads at a distant intersection at night, one with reflective border and clearly visible, one without border and lost amidst other lights.

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