01666008

Monograph

http://www.trb.org/Main/Blurbs/177422.aspx

This report documents the methodology and presents the results of a study aimed at estimating the safety effects of intersection sight distance (ISD) at stop-controlled intersections. To establish the relationship between ISD and safety at stop-controlled intersections, crash, traffic, and geometric data were collected for 832 intersection approaches with minor road stop control in North Carolina, Ohio, and Washington. These intersections represented a range of traffic volumes and major road cross section geometrics (e.g., two-lane, undivided; four-lane, undivided; four-lane, divided) in both urban and rural areas. Sites were selected for data collection without considering historic crash frequencies and severities. The data collection included field-measured ISD as a continuous variable using a standardized method as well as an exploratory measure of ISD quality. A cross-sectional study design with count regression modeling was used to quantify the relationship between safety and ISD. Target crashes were defined as those where a vehicle on the minor road collided with a vehicle on the major road. Target crash counts were associated with specific, measured values of an approach level ISD (i.e., one observation of target crash frequency in the database represents the target crash frequency for one minor road and major road approach combination). The results suggest that the expected numbers of target crashes and target fatal and injury crashes are associated with available ISD. Target crash frequencies increase as available ISD decreases. ISD quality may also impact safety performance, but it was not included in ISD crash modification functions (CMFunctions) that were created as part of this research. Results also suggest that ISD is associated with the expected number of target crashes in a non-linear fashion. The sensitivity of the expected number of target crashes to changes in ISD is highest when ISD is shorter, and decreases as ISD increases (i.e., the safety benefit of increasing ISD from 300 to 600 feet is substantially larger than the safety benefit of increasing ISD from 1,000 to 1,300 feet). Moreover, the results suggest that the impact of ISD on target crashes and target fatal and injury crashes varies as a function of the major road two-way annual average daily traffic (AADT) and the major road speed limit. The sensitivity of the expected number of target crashes to changes in ISD increases as both major road traffic volume and speed limit increase.

NCHRP Project 17-59

English

119p

2018

NCHRP Web-Only Document

9780309474740

Contractor's Final Report

Digital/other

Appendices; Figures; References; Tables

Crash rates; Highway safety; Intersections; Sight distance; Traffic safety

Stop-controlled intersections

Design; Highways; Safety and Human Factors

TRIS, TRB, ATRI

Apr 13 2018 9:18AM