Developing crash modification factors for roundabouts using a cross-sectional method

Al-Marafi, Mohammad Nour; Somasundaraswaran, Kathirgamalingam; Ayers, Ron

doi:10.1016/j.jtte.2018.10.012

Cited by 13 publications

(10 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Novák et al (2018) found that entry design parameters significantly influence safety in terms of crash frequency and speeds at the roundabout, especially at the approach level. Similarly, Al-Marafi et al (2020) considered traffic and geometric features and their influences on the safety performance of roundabouts. It was found that increasing the number of entry lanes, entry width, entry radius, traffic volume, circulatory roadway width, weaving width, and speed limit positively affects roundabout safety.…”

Section: Literature Reviewmentioning

confidence: 99%

Safety evaluation of urban roundabouts in India: a safety performance function-based approach

Vinayaraj

Vedagiri

2022

TSR

View full text Add to dashboard Cite

There is a lack of comprehensive research in roundabout safety under non-lane-based traffic conditions, mainly due to the absence of relevant crash data and effective tools for safety evaluation. Safety Performance Function (SPF) is a suitable tool for providing valuable information related to factors which can potentially contribute to the likelihood of increasing traffic crashes. Currently, very limited studies are available to explain the usefulness of SPF in the vicinity of roundabouts, especially at non-lane-based traffic conditions. This study aims to develop an SPF model for assessing the safety evaluation at roundabouts as a whole (intersection level) and the approach level. Data corresponding to crashes in nineteen roundabouts with different geometric and traffic characteristics was used for model formulation. Crash data for five years (2015–2019) was obtained from the State Crime Records Bureau. An SPF model was developed using a negative binomial model with a log-link function based on the number of crashes, traffic characteristics, and geometry characteristics of the roundabouts. The proportion of powered two-wheelers, percentage of heavy vehicles, entry-angle, and weaving-length were all significantly related with higher crash occurrences at roundabouts, according to the findings. In contrast, the number of circulatory lanes, inscribed circle diameter, and presence of road lane marking were negatively associated with the increased crash occurrences at the roundabout vicinity. In addition to this, the overall crash rate significantly varies across roundabout sections due to the asymmetric effects of geometric and traffic characteristics. The developed SPF would best explain the relationship between geometric and traffic characteristics and the crash occurrence rate in non-lane traffic conditions. The findings of this study support the need to relook at design parameters for better movement at the roundabouts, thereby improving the existing facilities to enhance road users' safety, especially in developing countries. The proposed SPF tool would help engineers examine the safety of roundabouts in terms of design adequacy, quantifying the risk factors, and future crash predictions.

show abstract

Section: Literature Reviewmentioning

confidence: 99%

Safety evaluation of urban roundabouts in India: a safety performance function-based approach

Vinayaraj

Vedagiri

2022

TSR

View full text Add to dashboard Cite

show abstract

“…Crash prediction models were used by various researchers to explain the safety aspects at various levels based on the influence of geometric and traffic characteristics (6,15,(25)(26)(27)(28)(29)(30)(31)(32). The variables considered are radius at entry, the width of entry, angle to next leg, central island diameter, entry path radius, average annual daily traffic, number of approaches, and circulating lane number.…”

Section: Crash Prediction Modelsmentioning

confidence: 99%

“…It is impractical to collect the before-and-after study treatment data from developing countries such as India. To overcome this limitation, a few studies ( 25 , 32 ) estimated CMF values-based CMF functions, while considering the safety effects of geometrical and traffic features. In short, there are limited studies investigating the effects of safety evaluation at roundabouts through CMF using only the CS approach in non-lane-based heterogeneous traffic conditions.…”

Section: Research Backgroundmentioning

confidence: 99%

Developing Safety Performance Functions and Crash Modification Factors for Urban Roundabouts in Heterogeneous Non-Lane-Based Traffic Conditions

Vinayaraj

Vedagiri

2023

Transportation Research Record: Journal of the Transportation R

View full text Add to dashboard Cite

This study aims to develop safety performance functions (SPFs) and crash modification factors (CMFs) for the safety assessment of roundabouts as a whole and their components, especially at entry, exit, and circulating lanes. This study uses historical crash data collected over five years (2015–2019) from 21 roundabouts (78 approaches) situated in some of the major cities in India. SPF and CMF models were developed using negative binomial and cross-sectional approaches. Results show that the percentage of motorized two-wheelers, average daily traffic, central island diameter, entry angle, weaving width, departure width, number of lanes at approach, exit angle, exit width, posted speed limit, weaving length, circulating roadway width, road surface condition, number of circulatory lanes, central island height, and number of legs contribute to the crash occurrence in the roundabout vicinity. In addition to this, circulating roadway width, average daily traffic, and posted speed limit are the most influencing risk factors across the entire roundabout vicinity. Furthermore, an interesting fact is that, given the asymmetrical impact of geometric and traffic factors, the overall crash rate varies across roundabout segments. The findings of this study may be useful for updating the current design guidelines for roundabouts, considering the safety perceptive. Besides, the proposed SPF and CMF tools could be used to investigate the likelihood of crashes at roundabouts. Moreover, this model would help safety experts to implement adequate safety treatment in the vicinity of roundabouts under heterogenous non-lane-based traffic conditions.

show abstract

“…In cross-sectional observational studies (such as this study), CMFs are estimated to only represent correlations instead of causal relationships. HSM suggests using a before-after study approach to estimate CMFs with available roadway geometric data (e.g., shoulder width, vertical grade) ( 8 ); however, under a data-limited environment, when before-after studies are not feasible, CMFs are often estimated with a cross-sectional study approach based on jurisdiction-specific SPFs ( 30 – 32 ). SPF predicted crash frequencies can be used to estimate the CMFs by comparing multiple median types ( 19 ).…”

Section: Literature Reviewmentioning

confidence: 99%

Bayesian Approach to Developing Context-Based Crash Modification Factors for Medians on Rural Four-Lane Roadways

Yang

et al. 2021

Transportation Research Record

View full text Add to dashboard Cite

Rural four-lane roadways provide important transportation accessibility and mobility to populations in rural areas. It is a challenge for practitioners to determine cross-section types when both benefits and costs need to be considered. Crash Modification Factors (CMFs) are developed to evaluate the safety effectiveness of alternative designs. However, safety effectiveness could vary significantly across contexts. Thus, this study aims to estimate CMFs for alternative cross sections of rural four-lane roadways under different contexts characterized by traffic volume, truck percentage, and access point density. Using Georgia state-wide crash data, this study developed Safety Performance Functions (SPFs) to predict crash frequencies for different contexts. Considering linearity and independence assumptions of traditional negative binomial SPFs, this study adopts Bayesian generalized negative binomial modeling approaches to relax those assumptions and only follows the Bayes rule to form SPFs for CMF estimation. This study focuses on four typical cross-sections including: (1) non-traversable medians; (2) two-way-left-turn lanes; (3) 4-ft flush medians; and (4) undivided roadways with double-yellow lines (the base cross-section design). The results show that CMFs vary significantly across different contexts. Compared with the base cross-section design, safety benefits of the other three designs can be either positive or negative under different traffic or road conditions. For example, 4-ft flush medians are found to have positive safety benefits (CMF < 1) under lower average daily traffic volumes (e.g., ≤ 6,000) and negative benefits (CMF > 1) under greater average daily traffic volumes (e.g., ≥ 15,000). The findings suggest that, to enhance roadway safety, practitioners should vary cross-section designs for different rural contexts.

show abstract

Developing crash modification factors for roundabouts using a cross-sectional method

Cited by 13 publications

References 26 publications

Safety evaluation of urban roundabouts in India: a safety performance function-based approach

Safety evaluation of urban roundabouts in India: a safety performance function-based approach

Developing Safety Performance Functions and Crash Modification Factors for Urban Roundabouts in Heterogeneous Non-Lane-Based Traffic Conditions

Bayesian Approach to Developing Context-Based Crash Modification Factors for Medians on Rural Four-Lane Roadways

Contact Info

Product

Resources

About