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Evaluating the Safety Effects of Driver Feedback Signs and Citywide Implementation Strategies
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- Author / Creator
- Wu,Mingjian
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Speeding is a leading factor that contributes to about one-third of all fatal collisions. To improve drivers’ compliance with speeds, various passive/active countermeasures have been adopted by municipalities around the world. A Driver Feedback Sign (DFS) is one such countermeasure as it dynamically displays the speed of the driver and warns them if they are speeding. It is relatively new, but it has the added advantage of being a low-cost intervention tool and its use is growing in urban centers worldwide. Despite documentation showing that DFSs are effective at reducing speeds, literature on its impact for reducing collisions is limited. This research serves to add to and advance the body of research into DFSs impact on traffic safety.
This research was completed in two phases. Phase I is a before-and-after study with the Empirical Bayes (EB) method to examine the effects DFSs have on reducing collisions. Safety Performance Functions (SPF) and yearly calibration factors were developed to quantify the sole effectiveness of DFSs using a large-scale spatial dataset of reference road segments. Afterwards, a detailed economic analysis was conducted to investigate the cost-effectiveness of DFSs.
As many municipalities’ budgets and resources are limited, Phase II of the thesis makes use of the methods and findings from Phase I to develop a location allocation framework to aid in determining the optimal implementation strategy for DFSs for two scenarios, an all-new scenario and an expanded scenario. The all-new scenario would represent a case of moving all existing DFS to optimal locations or for a completely new DFS system. The expanded scenario takes the existing DFS system and finds optimal locations where new DFSs should be installed. This optimization framework makes use of the safety effectiveness of DFSs and its spatial coverage for vulnerable road users as factors. By assigning different weights to these factors, transportation agencies can make a preference for either one over the other. The greedy algorithm was employed to solve the combinatorial optimization problem.
The case study area is the City of Edmonton, Alberta, Canada where they have been using DFSs since 2011 and to date has installed 212 DFSs throughout the city. The City has a large and vastly varied road network with an extensive history of DFSs and other speeding countermeasures. The data set used was provided by the City and encompasses collision data, locations of school and senior housing, traffic volumes, and road geometry over 10 years. This thesis makes use of these large data sets for both Phase I and II. The main findings of this thesis are summarized below.
Phase I results showed significant collision reductions that ranged from 32.5% to 44.9%, with the highest reductions observed for severe speed-related collisions. The economic analysis found that the benefit-cost ratios, if combining severe and Property-Damage-Only collisions, ranged from 8.2 to 20.2 indicating that the DFS can be an extremely economical countermeasure. The combined use of both DFS and mobile photo enforcement (MPE) was found to result in a slightly higher effect on safety. Before-after change models suggested that segments with higher initial collision frequencies, and generally with higher traffic volumes and longer road lengths, seem to benefit the most from the installation of DFSs. Additionally, the presence of shoulders was also found to impact the reduction in collisions for most collision types.
Phase II used the location allocation framework to develop a baseline of the City of Edmonton’s existing DFS deployment for comparison to the two previously mentioned scenarios. It was found that the collision frequency reduction and coverage of vulnerable road users/facilities can be improved by up to 149.44% and 69.27%, respectively, in the all-new scenario. The expansion scenario study was done with 10 and 20 additional units to the system. It was found that collision frequency reductions can be improved by up to 30.22% and 51.61% for the additional 10 and 20 DFSs respectively, depending on the weights being used. Likewise, the coverage of vulnerable road users/facilities could be improved by up to 14.64% and 29.27% respectively.
Overall, the approaches proposed and developed in the thesis provide a new and innovative method to quantify the sole effects of DFSs on road safety. By linking risk factors that contributed to the collision reductions and increase at DFS location with various city-wide DFS implementation strategies developed herein, this research helps to provide transportation agencies in need of implementing cost-effective countermeasures with a tool they need to design a long-term strategic DFS deployment plan to ensure the safety of travelling public and thus maximize the return on their investment. -
- Graduation date
- Spring 2020
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.