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


Ed Miska, PTOE, P.Eng., Senior Electrical and Traffic Engineer, BC Ministry of Transportation, Victoria, BC.

Paul de Leur, Ph.D., P.Eng., Road Safety Engineer, Insurance Corporation of British Columbia and the BC Ministry of Transportation, Vancouver B.C.

Tarek Sayed, Ph.D., P.Eng., Professor of Civil Engineering, University of British Columbia, Vancouver British Columbia.

Table of Contents:
1.0: Introduction
2.0: Hypothesis
3.0: Background and Early Installations
4.0: Installation Costs
5.0: Using Prediction Models for Road Safety Analysis
6.0: Data for Road Safety Evaluation
7.0: Methodology to Estimate the Safety Improvement Effects
8.0: Results and Discussion

The lack of traffic signal conspicuity is often cited as a contributing factor by drivers who are involved in accidents at intersections. As such, increasing the conspicuity of traffic signals should lead to improved safety performance. This paper describes a project to determine the road safety effectiveness associated with improved signal conspicuity. The project described in this paper was conducted in two phases. Phase 1 investigated the impact of improved signal head design on road safety performance. In Phase 2, the conspicuity of standard signal backboards was increased by adding yellow diamond grade reflective tape along the outer edge. This was done in an attempt to frame the signal heads and make them more visible to motorists, with the intent of improving intersection safety.

A time-series evaluation was completed to investigate the effectiveness of the improvements to the traffic signal on road safety performance. The use of comparison groups, prediction models and an Empirical Bayes analysis technique was used to account for the problematic confounding factors associated with road safety evaluation and ensure that the results are reliable. Anecdotal information concerning the effectiveness of the improved traffic signals were also collected and evaluated.

The British Columbia Ministry of Transportation has partnered with the Insurance Corporation of British Columbia on a multi-year program to upgrade all primary signal displays to the improved design. This paper quantifies and describes how the improved signal design and the use of diamond grade yellow tape at signalized intersections can provide cost-effective road safety benefits.

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