Karla A Polivka

Midwest Guardrail System for Standard and Special Applications

Development, testing, and evaluation of the Midwest Guardrail System were continued from the original research started in 2000. This new strong-post W-beam guardrail system provides increased safety for impacts with higher-center-of-mass vehicles. Additional design variations of the new system included stiffened versions using reduced (half and quarter) post spacings as well as a standard guardrail design configured with a concrete curb 152 mm (6 in.) high. All full-scale vehicle crash tests were successfully performed in accordance with the Test Level 3 requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The research study also included dynamic bogie testing on steel posts placed at various embedment depths and computer simulation modeling with BARRIER VII to analyze and predict dynamic guardrail performance. Recommendations for the placement of the original Midwest Guardrail System as well as its stiffened variations were also made.

Performance of Steel-Post, W-Beam Guardrail Systems

On the basis of the proposed changes to the NCHRP Report 350 guidelines, NCHRP Project 22-14(2) researchers deemed it appropriate to first evaluate two strong-post W-beam guardrail systems before finalizing the new crash testing procedures and guidelines. For this effort, the modified G4(1S) W-beam guardrail system and the Midwest Guardrail System (MGS) were selected for evaluation and comparison. Five full-scale vehicle crash tests were performed with the two longitudinal barrier systems, in accordance with the Test Level 3 (TL-3) requirements presented in the NCHRP Report 350 Update. For the modified G4(1S) testing program, two 2,270-kg pickup truck vehicles (2270P vehicles) were used: one 3/4-ton, two-door vehicle and one 1/2-ton, four-door vehicle. For the MGS testing program, two 2,270-kg pickup truck vehicles (2270P vehicles) and one 1,100-kg small-car vehicle (an 1100C vehicle) were used, with both pickup truck configurations being evaluated. On the basis of several findings, the NCHRP Project 22-14(2) researchers determined that the 1/2-ton, four-door pickup truck was better suited for use as a surrogate light truck test vehicle than the 3/4-ton, two-door pickup truck. The modified G4(1S) W-beam guardrail system, mounted at the top rail height of 706 mm, provided acceptable safety performance when it was crashed into by the 1/2-ton, four-door pickup truck vehicle, thus meeting the proposed TL-3 requirements presented in the NCHRP Report 350 Update. Testing of the modified G4(1S) W-beam guardrail system was not successful with a 3/4-ton, two-door pickup truck under the TL-3 impact conditions. The MGS was found to meet the TL-3 criteria presented in the NCHRP Report 350 Update for Test Designations 3-10 and 3-11. Satisfactory safety performance was observed with the MGS with both the 1/2-ton, four-door and 3/4-ton, two-door pickup truck vehicles.

Midwest Guardrail System W-Beam-to-Thrie-Beam Transition

For longitudinal barriers, it is common practice to use a standard W-beam guardrail along the required highway segments and to use a stiffened thrie-beam guardrail in a transition region near the end of a bridge. As a result of the differences in rail geometries, a W-beam-to-thrie-beam transition element is typically used to connect and provide continuity between the two rail sections. However, the W-beam-to-thrie-beam transition element has not been evaluated according to current impact safety standards. Therefore, an approach guardrail transition system, including a W-beam-to-thrie-beam transition element, was constructed and crash tested. The transition system was attached to Missouris thrie-beam and channel bridge railing system.

Midwest Guardrail System Adjacent to a 2:1 Slope

A W-beam guardrail is often used to protect motorists from steep roadside slopes adjacent to high-speed roadways. Although previously designed systems have demonstrated acceptable safety performance, the long posts and half-post spacing have proven to be costly and introduce maintenance challenges. Using longer posts is more economical to users than having a system with posts installed at half-post spacing. Furthermore, the improved redirective capacity of the Midwest Guardrail System (MGS) provides the opportunity to eliminate the need for half-post spacing and thereby greatly reduces the cost of placing a barrier at the slope break point. A stiffened version of the MGS was developed for use adjacent to steep roadside slopes. The new design incorporates 2,743-mm (9-ft) long posts with 1,905-mm (75-in.) spacing. With the top of the W-beam mounted at a height of 787 mm (31 in.), this guardrail was successfully crash tested according to the currently proposed NCHRP Report 350 Update safety performance evaluation criteria. Hence, the stiffened MGS guardrail design with full post spacing is acceptable for use on the National Highway System. This new guardrail design will provide a safe and economical alternative for use along highways with steep slopes very close to the travelway.

Long-Span Guardrail System for Culvert Applications

A long-span guardrail for use over low-fill culverts was developed and successfully crash tested. The guardrail system was configured with 30.48 m of nested, 12-gauge W-beam rail and centered around a 7.62-m-long unsupported span. The nested W-beam rail was supported by 16 W152×13.4 steel posts and 6 standard CRT posts, each with two 150-mm×200×360 mm wood block-outs. Each post was 1830 mm long. Post spacings were 1905 mm on center, except for the 7.62-m spacing between the two CRT posts surrounding the long span. The research study included computer simulation modeling with Barrier VII and full-scale vehicle crash testing, using 3/4-ton (680-kg) pickup trucks in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350. Three full-scale vehicle crash tests were performed. The first test was unsuccessful because of severe vehicle penetration into the guardrail system. This penetration resulted from a loss of rail tensile capacity during vehicle redirection when the swagged fitting on the cable anchor assembly failed. A second test was performed on the same design, which contained a new cable anchor assembly. During vehicle redirection, the pickup truck rolled over and the test was considered a failure. The long-span system was subsequently redesigned to incorporate double block-outs on the CRT posts and crash tested again. Following the successful third test, the long-span guardrail system was determined to meet TL-3 criteria.

Guardrail connection for low-fill culverts

A W-beam guardrail system was developed for attachment to the top slab of a low-fill concrete culvert. The guardrail design was constructed with a single, 2.66-mm-thick W-beam rail totaling 53.34 m in length. Over the culvert, W150×13.5 steel posts 946 mm long spaced 952.5 mm on center supported the W-beam rail. The research study included dynamic testing with a bogie vehicle and steel posts attached to a rigid foundation, computer simulation modeling with BARRIER VII, and two full-scale vehicle crash tests. The crash tests used three-quarter-ton pickup trucks and were conducted in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The first test was successfully conducted on the guardrail system with the back sides of the posts positioned 457 mm away from the front of the culvert’s headwall. The second test was unsuccessfully performed on the guardrail system with the back sides of the posts positioned 25 mm away from the front of the headwall. The safety performance of the W-beam guardrail system attached to the top of a low-fill concrete culvert was determined to be acceptable according to the TL-3 criteria found in NCHRP Report 350. Recommendations for the final placement of the guardrail system with respect to the culvert headwall are also made.

W-beam guardrail adjacent to a slope

A W-beam guardrail system was developed and successfully crash tested for use on a 2:1 foreslope. The guardrail design was constructed with W-beam rails 2.66 mm thick (12 gauge) totaling 53.34 m in length, and it incorporated a half-post spacing section of 17.15 m. The W-beam rail was supported by 15 W150 × 13.5 steel posts 1829 mm long, spaced 1905 mm on center, and 19 W150 × 13.5 steel posts 2134 mm long, spaced 952.5 mm on center. Routed, 150 × 200 × 360 mm wood spacer blockouts were used to block the rail away from each post. The research study included bogie testing on steel posts placed in sloped fill, computer simulation modeling with BARRIER VII, and one full-scale vehicle crash test, using a 2000-kg pickup truck. The test, impacting at a speed of 100.7 km/h and an angle of 28.5 degrees, was conducted and reported in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350. The safety performance of the W-beam barrier system was determined to be acceptable according to TL-3 criteria.

Crash Testing and Analysis of Work Zone Sign Supports

A variety of traffic-controlling devices are used in work zones; some of these are not normally found on the roadside or in the traveled way outside of the work zones. These devices are used to enhance the safety of the work zones by controlling the traffic through these areas. Because of the placement of the traffic control devices, the devices themselves may be potentially hazardous to both workers and errant vehicles. The impact performance of many work-zone traffic control devices is mainly unknown, and to date limited crash testing has been conducted under the criteria of NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The results of full-scale crash testing of flexible panel work-zone sign stands were evaluated and analyzed to quantify the features that successful devices shared, as well as common features of those devices that failed salient safety criteria. Parameters considered included sign base and upright properties, sign height, cross-member properties, and ancillary details. Results pointed to three problematic, fundamental design issues: (a) combinations of base and upright stiffness and strength that generally lead to significant windshield damage, (b) cross members that lead to windshield damage in the end-on (90°) impact orientation, and (c) appurtenances that have an impact on performance. Although there are a significant number of variables that control the performance of a given device, these generalizations offer a basis for the evaluation of the fundamental design elements.

Safety Grates for Cross-Drainage Culverts

This paper presents findings of an investigation of the safety performance of culvert safety grates when installed on slopes as steep as 3:1, as recommended by the AASHTO Roadside Design Guide (RDG). LS-DYNA modeling was used to identify critical impact conditions for roadside culvert grates installed on 3:1 slopes. Two full-scale vehicle crash tests were conducted under the guidelines of NCHRP Report 350 on a 6.4- × 6.4-m (21-×21-ft) culvert safety grate installed on a 3:1 slope. The full-scale crash tests demonstrated that the AASHTO RDG recommended safety grates provide acceptable safety performance when installed on 3:1 slopes.

Test Level 4 Noise Wall for Attachment to Concrete Traffic Barriers

A new transparent noise barrier system was developed for use on rigid bridge railings and other rigid structures. The crashworthy noise barrier system incorporated specially designed, strategically located structural hardware into a noncrashworthy noise barrier system. The noise barrier system was anchored to the back face of a reinforced concrete parapet with vertical steel posts. Transparent sound panels surrounded by a metallic frame were dropped between the spaced posts to create a noise barrier. Three horizontal rails were used to prevent errant vehicles from penetrating into sound panels, snagging on the support posts, or both. The test installation consisted of a 34.56-m-long Paraglas Soundstop TL-4 noise barrier system supported by 18 steel posts. Two full-scale crash tests—one with a single-unit truck and one with a pickup truck—were conducted and reported in accordance with the requirements specified in NCHRP Report No. 350: Recommended Procedures for the Safety Performance Evaluation of Highway...