SWUTC Research Project Description
Safety Performance of Different Types of Freeway Weaving Segments
University: Texas Southern University
Principal Investigator:
Yi Qi
Center for Transportation Training and Research
(713) 313-6809
Project Monitor:
Jun Yao
Transportation Specialist
Stantec
Funding Source: USDOT
Total Project Cost: $56,200
Project Number: 600451-00045
Date Started: 5/1/13
Estimated Completion Date: 5/31/14
Project Summary
Project Abstract:
Freeway weaving segment represents a stretch of freeway formed between merge (entrance ramps) and diverge points (exit ramps), over which traffic streams cross paths through lane-changing maneuvers. At freeway weaving segments, the design of ramp roadways, auxiliary lane, and continuity of lanes have significant effects on the roadway level of service and traffic safety. The objective of this study is to investigate the safety performance of three most representative types of freeway weaving segments, which have varying lane arrangements in term of ramp roadways and auxiliary lanes. The potential approaches will include crash data analysis, statistical modeling, and field inspection. The outcomes of this project will provide traffic engineers with necessary understanding of the critical issues associated with design of freeway weaving segments.
Project Objectives:
The goal of this research is to investigate the safety performance of three representative types of freeway weaving segments. The potential approaches will include crash data analysis, statistical modeling, and field inspects. To achieve this goal, the researchers will:
- Collect data concerning traffic, geometric, pavement markings, and information on crashes (crash rate, severity, collision type, and potential cause) at three different types of freeway weaving segments;
- Identify contributing factors to the crashes;
- Develop models for predicting crash rates/frequencies at different types of freeway weaving segments, as well as crash modification factors (CMF) accounting for different geometric features;
- Provide recommendations based on the outcomes of the research.
Task Descriptions:
Task 1: Review Literature
The purpose of this task is to conduct a thorough literature review. The areas to be reviewed include, but are not limited to (1) existing design standards and best practices for designing freeway weaving segments, and (2) safety performance of freeway weaving segments.
Task 2: Conduct Data Collection
The purpose of this task is to design and conduct a data collection at selected weaving segments, which have varying lane arrangements in terms of ramp roadways, lane connectivity, and auxiliary lane settings. The field study aims at providing necessary data for the safety analysis in the following tasks. More than 15 locations will be selected, which will cover three different types of freeway weaving segments. At each selected freeway weaving segment of three types, freeway surveillance videos will be recorded and all the relevant information will be collected. The data to be collected includes the traffic, geometric, and pavement markings conditions at each segment. Information on crashes occurred at the selected segments, e.g. crash rate, severity, collision type, and potential causes to the crashes, will also be collected from the TxDOT Crash Record Information Systems (CRIS).
Task 3: Develop Safety Models for Freeway Weaving Segments
In this task, models for predicting crash rates or frequencies will be developed for freeway weaving segments based on the traffic and geometric conditions. Statistical modeling approaches, such as negative binomial regression, analysis of factors, and correlation analysis will be used.
Task 4: Identify Contributing Factors to Crashes at Freeway Weaving Segments and Develop CMFs
In this task, contributing factors to the crashes at freeway weaving segments will be identified through (1) collision diagramming, (2) analysis of statistical regression results, and (3) field inspection when necessary. Following the AASHTO Highway Safety Manual methodology, crash modification factors will be developed to count for the safety impacts of different geometric features at freeway weaving segments.
Task 5: Document Research Findings
The purpose of this task is to document all the research findings from Tasks 1 to Task 4. A final report will elaborate the work performed, methods used, and results achieved.
Implementation of Research Outcomes:
The intensive lane change maneuvers at weaving sections often result in safety and operational problems. Various factors, including the design of ramp roadways, use of auxiliary lanes, and continuity of lanes will have significant effects on the level of service and safety performance of the weaving sections. This study investigated the safety performance of freeway weaving sections and developed a quantitative model for predicting the safety impacts of different types of geometric treatments for freeway weaving sections.
This study produced a new model for predicting the crash frequencies of freeway weaving segments. This is a unique model that can take account of the impacts of various factors, including the length of weaving section and the minimum required lane changes for merging or diverging vehicle. The impacts of these factors cannot be directly found in the current Highway Safety Manual.
Products developed by this research:
Presentation: Safety Performance of Freeway Weaving Sections, Qi, Y., X. Chen and J. Liu. Accepted for Presentation at TRB 94nd Annual Meeting, January, 2015.
Presentation: Safety Performance of Different Types of Freeway Weaving Segments, J. Liu and Y. Qi, , presented at TSU Research Week, April 3, 2014.
Model Developed: A model was developed for predicting crash frequencies of freeway weaving segments based on the traffic and geometric conditions.
Crash Modification Factors Developed: Crash modification factors (CMFs) were developed for projecting the change in crash frequency, given a specific safety treatment for a freeway weaving segment.
Impacts/Benefits of Implementation:
The results of this project provide guidelines to transportation engineers in the design of freeway weaving segments and assessing the safety impacts of various influencing factors. The developed methods, tables, models can be incorporated into the state or Federal roadway design manuals and the Highway Safety Manual. Resulting in reduced crash rates at freeway weaving segments. Thereby, it will also reduce social and environmental cost associated with the traffic accidents.
Web Links:
Final Technical Report