Study Details
Study Title: Crash Modification Functions for Pavement Surface Condition and Geometric Design Indicators
Authors: Cafiso et al.
Publication Date: 2021
Abstract: The combined contribution to highway safety of pavement surface and geometric design indicators is not well
investigated due to the complexity of data collection and high time variability of pavement surface conditions.
Introduction of high efficiency equipment for comprehensive road surveys is mitigating this issue, expanding
possibilities of data integration. In this framework, the present study developed crash modification functions
(CMFs) of pavement surface and geometric design indicators for different crash types (total, run-off-the-road, and
others), pavement conditions (dry and wet), and lighting conditions (daytime and nighttime) based on data from
two-lane rural highways in Italy. Geometric and pavement data were surveyed with the Automatic Road
Analyzer and the Grip Tester. Pavement surface condition data were corrected to the crash time by pavement
performance deterioration models based on traffic load to account for the variation in pavement conditions over
time. Crash, traffic and weather data were retrieved from national and local databases. This study used safety
performance functions (SPFs), fitted with generalized linear modelling techniques and a negative binomial
distribution error structure, for developing CMFs. The SPFs were used to quantify the effect of a specific variable
on crash occurrence and CMFs were then derived from the model coefficients. CMFs were developed for the
following parameters: Grip Number, International Roughness Index, curvature change ratio, coefficient of
variation of the curvature, maximum superelevation deficiency, and minimum lane width.
According to the study results, an increase in friction, as measured by the Grip Number, is associated with a
reduction in crash frequency while an increase in roughness, as measured by the International Roughness Index,
is associated with an increase in crash frequency. Thus, both pavement maintenance treatments aimed at
increasing friction as well as treatments aimed at reducing irregularities have a positive safety effect, especially
when wet, run-off-the-road or nighttime crashes are overrepresented. Study results allow to effectively integrate
pavement management systems and safety management systems. When developing paving schedules, transportation
agencies often base their decisions on asset management condition targets but do not explicitly account
for the role of pavement conditions in highway safety. Availability of CMFs for both pavement surface parameters
as well as geometric design parameters is crucial to improve pavement and geometric characteristics
considering their safety effects.
Study Citation: Cafiso, S., A. Montella, C. D'Agostino, F. Mauriello, F. Galante. "Crash modification functions for pavement surface condition and geometric design indicators". Accident Analysis and Prevention, Vol 149, (2021) pp. 105887.
Study Report: Download the Study Report Document
CMFs Associated With This Study
Category: Roadway
Countermeasure: Change in pavement roughness
CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
---|
| | | All | All | Not specified | Rural |
| | | Run off road | All | Not specified | Rural |
| | | Other | All | Not specified | Rural |
| | | Dry weather | All | Not specified | Rural |
| | | Day time | All | Not specified | Rural |
| | | Nighttime | All | Not specified | Rural |
| | | Run off road | All | Not specified | Rural |
| | | Other | All | Not specified | Rural |
| | | Dry weather | All | Not specified | Rural |
| | | Wet road | All | Not specified | Rural |
| | | Day time | All | Not specified | Rural |
| | | Nighttime | All | Not specified | Rural |