Placement of Guardrails on Slopes (405160-4):
PROBLEM STATEMENT
The AASHTO Roadside Design Guide recommends that guardrail be installed with the back edges of the guardrail post being 2 ft from a slope break. In many mountainous areas or in locations with tight environmental controls this width is difficult to provide. As a result, designers often have to make a trade-off between reduced shoulder width and a less than optimal guardrail placement. The WSDOT Design Manual provides for the placement of the guardrail post closer to or on slopes as steep as 1H:1V. A research effort undertaken by Polivka et al (October 2000) of the Midwest Roadside Safety Facility (MwRSF) recommended a design with a 7 ft long posts spaced at 3 ft o.c. with the post placed at the slope break to a 2H:1V slope. However, in many cases, steeper slopes are encountered and more width is desired.
BACKGROUND
Earliest known research about guardrail placement on slopes was conducted by ENSCO, Inc. (1988) which included a battery of pendulum tests on a single post and three full scale crash tests. Two tests of a large sedan impacting a G4(1S) guardrail system installed on a break point of a 2H:1V slope were considered to be successful to redirect the sedan per NCHRP Report 230. One of the tests had a 6 ft post length while the other had a 7 ft post length. The 7 ft post length installation had a better performance (rail deflection and vehicle impact speed change) than the 6ft post length installation.
Polivka et al (October 2000) conducted another battery of bogie tests and a crash test of steel post guardrail system with a 2000P test vehicle per NCHRP Report 350 Test level 3. A region that encompassed the impact point had 7 ft long W 6X8.5 steel posts placed 3 ft 1.5 inches on center. These posts were placed on the break of 2H:1V slope with 4 ft 7 inch embedment depth. The crash test was considered successful per NCHRP Report 350 test evaluation criteria.
OBJECTIVE
This study would investigate the sensitivity of standard guardrail to the placement in front of or on a slope and would develop alternate methods for installing guardrail in front of or on slopes steeper than 2H: 1V.
BENEFITS
This research would determine if there is a need for improvements in the design of beam guardrail when placed in front of or on slopes that are 2H:1V or steeper and identify alternate designs that might be explored further.
FULL-SCALE CRASH TEST:
On April 16, 2008, a full-scale crash test was performed on the selected W-beam guardrail on 2H:1V slope design. A 2000 GMC C2500 pickup (weight of 4610 lb) impacted the guardrail at an impact speed of 62.3 mi/h and an impact angle of 25.1 degrees. Impact point was at post #15 (6th post from beginning of ditch), as shown in the following drawing:
CIP for guardrail on slope test 3-11
Sequence Shots:
The vehicle was redirected, but subsequently came to rest on its side.
Videos of crash test:
Pan Shot (real time)
Rear of Vehicle View (real time)
High-Speed Frontal View of Vehicle
High-Speed Overhead View
High-Speed Field Side of Barrier View
FINAL REPORT
Quarterly Progress Reports:
October 2008 Progress Report
July 2008 Progress Report
March 2008 Progress Report
December 2007 Progress Report
September 2007 Progress Report
June 2007 Progress Report
March 2007 Progress Report
January 2007 Progress Report
October 2006 Progress Report
July 2006 Progress Report
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