Calibration of Highway Safety Manual Safety Performance Function

Brimley, Bradford K.; Saito, Mitsuru; Schultz, Grant G.

doi:10.3141/2279-10

Cited by 85 publications

(24 citation statements)

References 12 publications

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“…In order to determine the overall CMF, it is necessary to compute the weighted average log odds ratio (R) across all of the treated sites, according to Equation (14) and as explained in the methodology section. When the R-value is known, the overall CMF can be easily estimated according to Equation (15) in the methodology section.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

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Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach

et al. 2018

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In the summer of 2011, a change in the Kansas laws came into effect, increasing the speed limit on a selected set of freeway sections from 70 mph to 75 mph. Higher speeds were thought to have economic benefits, mostly because the travel time reduction means people reach their destinations more quickly. In this study, the sections where the speed limits remained unchanged, are compared to freeway sections that have been influenced by speed limit increase, to evaluate safety effectiveness. The study utilizes the before-and-after study with comparison group method to assess the safety effects provided in the Highway Safety Manual (HSM). Two crash datasets, obtained by considering three years before and three years after the speed limit increase, were compared in order to evaluate the safety effects of the speed limit change. The crash modification factors (CMFs) were estimated, which showed that there was a 27% increase in total crashes and a 35% increase in fatal and injury crashes across all sections after the speed limit change, and these increases were statistically significant at 95% confidence level. These confounding results show that the speed limit increase has not been beneficial for traffic safety in Kansas, and hence it is important to be cautious in such future situations. Also, additional data have been presented which would be beneficial in identifying and understanding any behavior change in drivers following a speed limit increase.

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Section: Data Analysis and Resultsmentioning

confidence: 99%

“…There are some multi-lane highway sections where the speed limit remained unchanged. However, all the sections that received a speed limit change are freeways, which need specific SPF(s) for identifying the predicted crash frequency [15].…”

Section: Discussionmentioning

confidence: 99%

Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach

et al. 2018

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“…The results of the goodnessof-fit showed that the SPF developed presented a better fit than the model calibrated using the SPFs [5]. Other research calibrates the SPFs [5] and develops new models for two-lane rural roads in each direction in the state of Utah using 3 years of crashes reports [27] determining as significant variables the average annual daily traffic volume (AADT), segment length, speed limit and percentage of ADDT made up of trucks.…”

Section: Estimating Models Of Spfsmentioning

confidence: 99%

Safety performance functions in Dedicated Bus Lane of BRT on Caracas Avenue Corridor at Bogotá city

Polo

Pérez

2019

Inge Cuc

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Introduction- Road safety is a global concern due to the fact that traffic accidents represent serious temporary and / or permanent damage to the health of those involved. On the other hand, the Bus Rapid Transit (BRT) systems carries a large volume of passengers and during their operation; they are involved in this problem. Objective- Accident prediction model implemented in the Highway Safety Manual 2010 or HSM is an alternative to evaluate the strategies that allow to reduce accidents in this type of systems. However, there is not specified safety performance functions (SPFs) developed for BRT systems. In the present work, the accident model of HSM is adapted by calibration of general SPFs expressions of the manual and also, SPFs were developed for BRTs installed on the central-line of main roads and use an exclusive lane of all other transport systems (both public or private) and mobility (e.g. bike paths). Method / Results - Crashes reports and traffic volumes data supplied by the Department of Transportation of Bogotá were used. The model was calibrated using the safety performance functions (SPFs) of the HSM and a specific developed functions for the BRT conditions. These SPFs were developed using a negative binomial model in roadway segments and intersections. Conclusions- Through the validation, it was found that the functions developed have a better fit than the established SPF of the HSM. The developed SPFs can be used as a tool to define safety performance guidelines of Bogotá's BRT corridors in the coming years.

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“…On the other hand, estimating combined safety impacts of multiple countermeasures remain an unresolved key issue in HSM and just multiplication of the CMFs may lead to an over-or underestimation of combined effects [13]. In addition, AASHTO has addressed the failure in considering the local impact of different factors in HSM [14]. The duration of study for developing CMFs is another drawback, in that the research process requires data of traffic crashes before and after implementation of countermeasures.…”

Section: Introductionmentioning

confidence: 99%

Simulation-Based Framework for Estimating Crash Modification Factors (CMFs): A Case Study for ITS Countermeasures

Das

Park

Bhavsar³

2019

Journal of Advanced Transportation

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The efficient movement of users and goods is the primary purpose of the surface transportation system. Roadway traffic crashes have devastating impacts on quality of life of the users as well as health of the system. While researchers are utilizing advanced computing and communication tools to reduce number of crashes on the roadways, there is still an absence of appropriate method to evaluate the safety performances of these advanced technologies in the planning stage. Development of crash modification factors (CMFs) is a standard method to evaluate the safety effect of proposed countermeasures. Though, the current practices of developing CMFs are not efficient and cost-effective in case of addressing impacts of Intelligent Transportation System (ITS) countermeasures. This study demonstrated a proof of concept of simulation-based framework for determining CMFs for ITS countermeasures. The proposed framework includes the application of traffic microsimulation model and Surrogate Safety Assessment Model (SSAM) developed by Federal Highway Administration (FHWA). The integration of these two models is suggested to estimate CMFs efficiently. However, the calibration of traffic microsimulation model and SSAM model is essential to portrait the real-world scenarios. A case study for estimating CMFs of ITS countermeasures was conducted to validate the proposed simulation-based approach. Four ITS countermeasures were considered: ramp metering, variable speed limit, junction control, and dynamic lane assignment. They were coded in traffic microsimulation environment and vehicle trajectory files were generated to import into SSAM model. After analyzing these trajectory files in SSAM tool, it was found that all proposed ITS countermeasures, except variable speed limit assignment, could reduce the number of crashes at crash prone locations.

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Calibration of Highway Safety Manual Safety Performance Function

Cited by 85 publications

References 12 publications

Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach

Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach

Safety performance functions in Dedicated Bus Lane of BRT on Caracas Avenue Corridor at Bogotá city

Simulation-Based Framework for Estimating Crash Modification Factors (CMFs): A Case Study for ITS Countermeasures

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