Background
With its publication by AASHTO in October 2009, the Manual for Assessing Safety Hardware (MASH) has superseded NCHRP Report 350 as the recommended procedures for the safety performance evaluation of roadside features. The majority of longitudinal barrier crash tests are preformed on flat, level terrain. However, it is recognized that cable median barrier is commonly installed in a median ditch on sloped terrain. This practice accommodates the needed working width of the barrier and helps reduce the frequency of impacts. It is, therefore, desirable to test and evaluate cable median barriers in a ditch.
A question has arisen pertaining to what ditch configurations should be used to evaluate a cable median barrier that is designed to be placed anywhere in any ditch with 4H:1V slopes or flatter. The multitude of ditch configurations that exist in the field makes the selection of appropriate test conditions a challenge. Although a maximum slope is defined (e.g., 4H:1V), other variables include ditch width, shape, and degree of rounding of the hinge points.
Several crash tests have been conducted at the Midwest Roadside Safety Facility (MwRSF) at the University of Nebraska Lincoln (UNL) on a generic cable median barrier being designed for placement anywhere in a 4H:1V ditch. The testing was conducted in a relatively wide (42 ft) ditch and has included a barrier placed at the critical lateral offset on the foreslope and near the ditch bottom on the backslope.
Additional consideration is being given to the evaluation of cable barriers in a narrower (e.g., 30 ft) ditch. The narrower ditch width will result in vehicle interaction with the backslope during redirection. This interaction may or may not cause the pickup truck to become unstable. There is a need to evaluate and compare performance related to both ditch widths to determine which is more critical for use in future testing.
It has also been observed in previous testing of cable median barriers on the backslope of a narrow ditch, that a passenger car has the propensity to steer up the backslope before impacting the barrier. This behavior can induce a yaw opposite the direction of desired redirection. It has been proposed to further evaluate this test condition through additional testing.
Objective
The objective of this project is to conduct a full-scale crash test of a generic 4-cable median barrier in a narrow ditch with 4H:1V slopes – one on the ditch foreslope with a pickup truck, and one on the ditch backslope with a small car and develop and final matrix for updating and refining the MASH.
Tasks
Task 1. Conduct a Manual for Assessing Safety Hardware (MASH) Test 3-11 with a cable barrier placed on a 4H:1V ditch foreslope. (cancelled)
Amended Task 1. Develop cable median barrier test matrices using information from existing testing, simulation, and Delphi method approach.
Task 2. Conduct a MASH Test 3-10 with a cable barrier placed on a $H:1V ditch backslope.
Task 3. Submit a final report documenting the research approach and test results.
Status: Completed; final report sent to AASHTO.
