Karla A Lechtenberg

Guidelines for Implementation of Cable Median Barrier

A detailed examination of accidents in Kansas evaluated the need for a cable median barrier. Hard copies of all accident reports from Kansas controlled-access freeways from 2002 to 2006 were reviewed. A total of 525 cross-median events and 115 cross-median crashes were identified. Cross-median encroachment rates were linearly related to traffic volume and cross-median crash rates appeared to have a second-order relationship to volume. Cross-median crashes were much more frequent in winter months and the severity of wintertime crashes was lower. This finding indicates that median barrier warranting criteria may need to be adjusted to accommodate regional climate differences, especially for warranting guidelines based on cross-median crash rates. A relationship was found between cross-median crash rate and traffic volume for Kansas freeways with median widths of 60 ft (18.3 m). This relationship was combined with encroachment rate and lateral extent of encroachment data from the Roadside Safety Analysis Program to develop general guidelines on the use of cable median barriers along Kansas freeways.

High-Performance Aesthetic Bridge Rail and Median Barrier

Design of high-performance concrete barriers for heavy vehicles has advanced little in recent years. Barrier improvements were needed in terms of design aesthetics, safety performance, and economy. Advancement was deemed necessary for improved barrier geometry design to reduce vehicle instability and the potential for occupant head slap on the barrier, improved understanding of impact loads for heavy vehicles and use of these loads to optimize barriers, and improved barrier aesthetics. This paper describes the development of two NCHRP Report 350 Test Level 5 (TL-5) barriers that address these needed advancements. First, a TL-5 open concrete bridge rail was designed with a focus on determining accurate impact loads and providing a barrier geometry with improved safety and aesthetics. Next, a TL-5 concrete median barrier was developed through rigorous analysis of barrier shape options to determine the safest and most economic shape. Structural design of the barrier was also optimized to minimize cost while meeting the design loads for heavy vehicles. The open concrete bridge rail and the concrete median barrier were successfully full-scale crash-tested according to the TL-5 safety requirements set forth in NCHRP Report 350. These designs represent a major advancement in the safety and economy of high-performance concrete barriers.

Development and Implementation of the Simplified Midwest Guardrail System Stiffness Transition

The varied lateral stiffness between bridge rails and approach guardrail systems may cause vehicle pocketing or wheel snagging to occur near rigid bridge rail ends. To mitigate this potential hazard, an approach guardrail transition (AGT) is used to provide a gradual increase in the lateral stiffness of the barrier between the W-beam guardrail system and the bridge railing. However, these transitions can also cause a propensity for vehicle pocketing or wheel snagging if the change in lateral stiffness occurs too rapidly. Recently, a stiffness transition based on NCHRP Report 350 was developed for use with the Midwest Guardrail System (MGS) and a stiff Thrie beam AGT, and successful testing was performed close to the upstream end of the AGT. The transition was designed with three sizes of steel posts, one of which was nonstandard for state departments of transportation. Thus, a simplified version of the original MGS stiffness transition that used two common sizes of steel posts was developed and was subjected to full-scale crash testing according to Test Level 3 as set forth in the Manual for Assessing Safety Hardware. Subsequently, dynamic post properties obtained from bogie testing and numerical simulations were used to develop an equivalent wood post version of the simplified MGS stiffness transition. Recommendations are made regarding the attachment of the stiffness transitions to FHWA-accepted Thrie beam bridge rail AGTs.

Performance of the Midwest Guardrail System with Rectangular Wood Posts

Strong-post W-beam is one of the most enduring and prolific safety barriers in the world. Over the years, it has been modified and updated to improve performance. Throughout these changes, two types of guardrail posts have been used to support the rail element: W6 × 8.5 steel posts and 6-in.-wide × 8-in.-deep wood posts. Recent updates to roadside safety hardware evaluation criteria and concerns with the performance of the G4 (1S) and G4 (2W) strong-post W-beam systems have led to the need for enhanced strong-post guardrail designs. The Midwest Guardrail System (MGS) was developed to address this need and provides improved performance over previous strong-post W-beam systems. The MGS was developed and tested with steel support posts, and it was believed that the use of wood posts in the system would provide similar barrier performance. However, the effect of wood posts in the MGS was never quantified through full-scale crash testing. The objective of this study was to investigate and evaluate the performance of the MGS with rectangular posts made of southern yellow pine. This effort included a review of the performance of wood and steel guardrail posts as it pertained to the MGS, the completion of two full-scale crash tests according to the Manual for Assessing Safety Hardware (MASH) safety requirements, and a comparison of the full-scale test results with MASH safety criteria and previous steel-post and alternative species wood-post MGS tests. Finally, recommendations were developed to implement the wood-post MGS and wood posts in MGS special applications.

Racetrack SAFER barrier on temporary concrete barriers

Previously, the Steel and Foam Energy Reduction (SAFER) barrier system was successfully developed and crash tested for use in high-speed racetrack applications for the purpose of reducing the severity of racecar crashes into permanent, rigid, concrete containment walls. The SAFER barrier has been implemented at all high-speed oval race tracks that host events from NASCARs top three race series and IRLs top series. However, there are a number of racetrack facilities in the United States that use temporary concrete barriers as a portion of the track layout during races. These barriers are typically used on race tracks to shield openings or protect portions of the infield. Some of these temporary barrier installations are in areas where current safety guidance would recommend treatment with the SAFER barrier. Thus, a system was successfully designed, tested, and evaluated for a system targeted towards the most pressing need in the US motorsports industry, a system for spanning openings between rigid concrete parapets on the inner walls of various race tracks.

Nonblocked Midwest Guardrail System for Wire-Faced Walls of Mechanically Stabilized Earth

Wire-faced walls of mechanically stabilized earth (MSE) provide an economical method for building vertical structures for supporting roadways where local topography or high land costs preclude the use of conventional fill slopes. W-beam guardrail systems are often used for shielding high vertical drop-offs associated with MSE walls. For this study, the Midwest Guardrail System (MGS) was modified to decrease the overall width of the MSE wall structure. Dynamic component testing was used to determine the post–soil behavior of steel and wood posts embedded in compacted soil materials used for constructing wire-faced MSE walls as well as to evaluate the effects of sloped terrain and different installation methods. Twenty-six dynamic tests were performed to evaluate the propensity for MSE wall damage, to select post length, and to determine the preferred post material and section. The standard MGS was modified by removing the wood spacer blocks 12 in. (305 mm) deep and by incorporating W-beam backup plates. All other MGS features—including the W6 × 8.5 (W152 × 12.6) steel posts 6 ft (1.8 m) long, rail splices at midspan locations, the 31-in. (787-mm) top-mounting height, and the 75-in. (1,905-mm) post spacing—were maintained. The nonblocked MGS was installed with the posts driven at the slope break point of a 3H:1V fill slope. The modified MGS was successfully crash tested with both 1100C small car and 2270P pickup truck vehicles in accordance with Test Level 3 safety performance guidelines in the Manual for Assessing Safety Hardware. The MSE wall was not damaged during the testing programs. The nonblocked MGS is recommended for use with wire-faced MSE walls when they are placed at the slope break point of a 3H:1V fill slope. The modified MGS reduces the required width of the MSE wall, resulting in decreased construction costs.

Development of a Low-Cost, Energy-Absorbing Bridge Rail

A new, low-cost bridge railing was designed to be compatible with the Midwest Guardrail System (MGS). The barrier system was configured to reduce bridge deck width and its associated cost. Several concepts for an energy-absorbing bridge post were developed and tested; the concepts included strong-post designs with plastic hinges and weak-post designs with bending near the bridge deck attachment. The final railing concept incorporated S3 × 5.7 (S76 × 8.5) steel posts housed in a tubular bracket placed at the outside vertical edge of the deck and anchored to its top and bottom with one through-deck bolt. The W-beam rail section was attached to the posts with a bolt that was designed to fracture during an impact event. Two full-scale crash tests were performed in accordance with the Test Level 3 impact conditions provided in the Manual for Assessing Safety Hardware. The bridge rail system met all safety performance criteria for both the small car and pickup truck crash tests. Barrier VII computer simulations, in combination with the full-scale crash testing programs for the bridge railing and MGS, demonstrated that a special-approach guardrail transition was unnecessary.

Evaluating the Cost-Effectiveness of Roadside Culvert Treatments

Roadside cross-drainage culverts have been found to affect vehicle accident injury levels. As a result, highway designers have commonly used three safety treatments to protect errant motorists from striking culvert openings. These safety treatments have included: culvert extension, guardrail installation, and the application of safety grating. However, the identification of the most appropriate safety treatment for roadside culverts may be challenging; accident costs may dramatically change under different road and traffic characteristics. The purpose of this study was to estimate accident costs for a wide range of road and traffic scenarios and then define the safest treatment (i.e., treatment with lowest accident cost) for a variety of traffic, roadway, and roadside characteristics. Over 3,000 highway scenarios were modeled using the Roadside Safety Analysis Program (RSAP). This study showed that the selection of culvert safety treatments should be flexible when considering different road and traffic characteristics. The findings demonstrated that culvert extension and grating were found to produce the lowest accident costs for all highway scenarios that were modeled, and guardrail protection was not recommended for any of the scenarios. Therefore, it is believed that the expanded adoption of culvert extension and culvert grates can improve overall highway safety.

Cost-Benefit Analysis of Crash Cushion Systems

Crash cushions vary in geometry and cost. In this study, crash cushions were categorized in three different categories: redirecting with repair costs greater than

Midwest Guardrail System without Blockouts

1,000 (RGM), redirecting with repair costs less than