Erdong Chen

Effectiveness of cable barriers, guardrails, and concrete barrier walls in reducing the risk of injury

Roadway departure crashes tend to be severe, especially when the roadside exposes the occupants of errant vehicles to excessive injury hazards. As a cost-effective method when the clear zone width is insufficient, road barriers are often installed to prevent errant vehicles from colliding with dangerous obstacles or traversing steep slopes. This paper focuses on the safety performance of road barriers in Indiana in reducing the risk of injury. The objective of the study presented here is to compare the risk of injury among different hazardous events faced by an occupant in a single-vehicle crash. The studied hazardous events include rolling over, striking three types of barriers (guardrails, concrete barrier walls, and cable barriers) with different barrier offsets to the edge of the travelled way, and striking various roadside objects. A total of 2124 single-vehicle crashes (3257 occupants) that occurred between 2008 and 2012 on 517 pair-matched homogeneous barrier and non-barrier segments were analyzed. A binary logistic regression model with mixed effects was estimated for vehicle occupants. The segment pairing process and the use of random effects were able to handle the commonality within the same segment pair as well as the heterogeneity across segment pairs. The modeling results revealed that hitting a barrier is associated with lower risk of injury than a high-hazard event (hitting a pole, rollover, etc.). The odds of injury are reduced by 39% for median concrete barrier walls offset 15-18ft from the travelled way, reduced by 65% for a guardrail face offset 5-55ft, reduced by 85% for near-side median cable barriers (offset between 10ft and 29ft), and reduced by 78% with far-side median cable barriers (offset at least 30ft). Comparing different types of barriers is useful where some types of barriers can be used alternatively. This study found that the odds of injury are 43% lower when striking a guardrail instead of a median concrete barrier offset 15-18ft and 65% lower when striking a median concrete barrier offset 7-14ft. The odds of injury when striking a near-side median cable barrier is 57% lower than the odds for a guardrail face. This reduction for a far side median cable barrier is 37%. Thus, a guardrail should be preferred over a concrete wall and a cable barrier should be preferred over a guardrail where the road and traffic conditions allow. In the light of the results, installing median cable barriers on both sides of the median to reduce their lateral offset is beneficial for safety. The study also found that the unexplained heterogeneity across vehicles is much larger than it was across matched segment pairs.

Analysis of Crash Frequency in Work Zones with Focus on Police Enforcement

Highway work zone safety has been a concern nationwide and will likely draw ever increasing attention as more highway funds are invested in the maintenance of existing highways. To improve work zone safety, the Indiana Department of Transportation (DOT) established a special fund for work zone patrolling, and this study was commissioned to help the Indiana DOT achieve the maximum safety benefits within its budget constraint. With help from the Indiana DOT, a survey of project engineers was conducted to collect work zone information. The findings from the survey were linked with other available data. A random-effect negative binomial model was developed to identify the contributing factors and to estimate crash frequency in highway work zones. The results from the model provided insight for better understanding of crashes in work zones. Various factors, including roadway information, traffic volume, work zone–specific features, and police presence, were identified as things that affect crash frequency in work zones. These and other findings will be used to plan police enforcement activities in future Indiana DOT work zones.

Best Practices for INDOT‐Funded Work Zone Police Patrols

Transportation agencies across the U.S. are expending a great deal of effort to improve highway work zone safety. Among those efforts is a special fund for work zone enforcement established by the Indiana Department of Transportation (INDOT). The allocation of enforcement funding was based on expert knowledge and weights and scores applied to work zone characteristics considered relevant to traffic safety. The objective of the reported project was to develop a rational and defendable tool for programming police enforcement that maximizes the safety benefits of police enforcement in INDOT work zones. To understand what affects work zone safety, the research team carried out an extensive literature review, designed field experiments to evaluate the effect of selected enforcement strategies on drivers’ behavior in work zones, and developed speed models incorporating the effect of police enforcement. The estimated speeds were used to derive crash modification factors (CMFs) that express the effect of the police enforcement strategy on work zone safety. Finally, the research team combined all of the developed components in a method of predicting the costs and the safety benefits in work zones under various enforcement strategies. This last method was included in the optimization tool for programming police enforcement in a group of planned work zones. The described project developed an optimization tool implemented in a Microsoft Excel spreadsheet with the OpenSolver add‐in. The tool is flexible, straightforward, and easy to use. The user should be able to quickly become familiar with the required input, results, and obtained solution.

Use of Barriers in Rural Open Road Conditions—A Synthesis Study

The use of wide medians and clear zones that do not require median and roadside barriers is the current design practice for new and reconstructed rural highway facilities. Constructing or reconstructing roads with full-width medians and clear zones is much more expensive today compared to when the design standards were developed. Considerable costs can be accrued in additional overhead bridge length, earthwork and ROW in new construction projects, and widening of existing right–of-way and bridge structures in reconstruction projects. This synthesis study focuses on the use of median barriers and roadside barriers and it identifies: (a) the current design practice and the existing body of knowledge, (b) design conditions where adding extra traffic lanes without widening the ROW is acceptable from the point of view of safety and costs if barriers and guardrails are installed, and (c) future research needs. One of the practical outcomes of the project is a set of Crash Cost Modification Factors (concept found in the German design guidelines) estimated based on the past research for Indiana and simulation experiments executed with the Roadside Safety Analysis Program. These factors can be used to evaluate the safety benefit produced by a modified cross-section of a rural freeway.

Updating RoadHAT: Collision Diagram Builder and HSM Elements

were compared and their performance evaluated using Indiana data. The HSM models also were checked as to whether they would perform better in Indiana by calibrating them with Indiana data. A second major component of the study was to improve the current Indiana safety management tool, RoadHAT2, by developing a computer application facilitating preparation of a so-called collision diagram. These diagrams are an important component of safety audits. However, they are not used frequently due to the considerable time required to build collision diagrams.