The AASHTO Manual for Assessing Safety Hardware (MASH) provides a full-scale test matrix for evaluating cable median barriers on level terrain and sloped median ditches. The matrices define the critical placement of cable barriers and test criteria for 4:1 and 6:1 V-ditches to evaluate cable median barriers at various offsets or anywhere in a median V-ditch. Recent full-scale crash testing of cable median barriers mounted on the far side of a 4:1 V-ditch indicates that the 1100C small car vehicle may not be able to safely and consistently traverse a 4:1 V-ditch in MASH test no. 3-16.

The 4:1 V-ditch configuration in the MASH 2016 test matrix uses a 46-ft wide V-ditch as measured from slope break point to slope break point. This V-ditch was selected based on preliminary full-scale crash tests of cable median barriers in V-ditches, vehicle dynamics simulations, and LS-DYNA simulations. The 4:1 slope was selected based on the maximum V-ditch slopes desired by state departments of transportations (DOTs). The ditch width was selected based on ditch traversal simulations to provide for a ditch capable of evaluating the maximum vehicle override potential on the front slope, the maximum vehicle underride potential during when a vehicle bottoms out on the backside of the V-ditch, and the maximum vehicle override potential when a vehicle rebounded from the bottom of the ditch and traversed up the backside of the ditch. Additionally, the AASHTO Roadside Design Guide (RDG) notes that 4:1 V-ditches are not a preferred configuration for median V-ditches, while flat bottom median ditch configurations are at the limit of the preferred configuration guidelines. Thus, the traversability of the V-ditch configuration recommended in MASH 2016 may be near the limit of vehicle stability. 

The objective of this research is to further investigate the traversability of 4:1 V-ditches and determine any needed updates to the MASH cable median barrier test matrix to ensure consistent performance of these ditches when evaluating cable median barriers.