Abstract
To facilitate the evaluation of the safety performance of freeway merge, diverge, and weave areas, conventional crash-based Safety Performance Functions (SPFs) were developed using generalized linear models (GLM) with a negative binomial (NB) error structure. However, crash-based SPFs may not take into account all factors that contribute to the crashes. The use of simulated conflicts as a surrogate safety measure to predict crashes can address this issue and provide recommendations for the designs and traffic control strategies. This approach was explored by using Surrogate Safety Assessment Model (SSAM) and VISSIM software to generate and analyze conflicts for merge areas on Ontario freeways. Crash-conflict integrated SPFs with different Time to Collision (TTC) thresholds were then developed and compared. Their predictive capabilities were also evaluated. To complement this analysis, the transferability of US crash prediction models to Ontario data was evaluated and the goodness-of-fit of these models was explored.
Highlights
1.1 Road Safety IssuesTransportation problems such as the increased traffic congestion and amount of traffic collisions have become critical global challenges
The goodness-of- fit was determined by evaluating P- values, Mean prediction bias (MPB), Mean absolute deviation (MAD), Mean squared prediction error (MSPE), Mean squared error (MSE), k, and Cumulative Residual (CURE) plots for these models
Collision data for 22 sites were collected from auxiliary lanes and adjacent freeway mainline to develop the Safety Performance Functions (SPFs) for weave areas
Summary
Transportation problems such as the increased traffic congestion and amount of traffic collisions have become critical global challenges. The fatalities and injuries occurring in motor vehicle collisions lead to high costs for society. According to a report from Transport Canada 2007, the annual social costs of the 613,000 motor vehicle collisions regarding loss of life, medical treatment, rehabilitation, lost productivity, and property damage was around $62.7 billion (4.9% of Canada’s 2004 Gross Domestic Product). In terms of Ontario, the social cost generated by motor vehicle collisions in 2004 was $18 billion, in which fatalities made the largest single contribution of $11 billion (Vodden 2007; Heydari 2012). High speed and lane change maneuver behaviours can increase the risk of collisions on freeways. Designed ramps with inappropriate speed-change lanes could result in high frequency of collisions
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