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Our maintenance department likes the detail from WashDOT shown below.

We are looking to upgrade to only MASH TL-4 HTC.

I'm concerned that the end anchor of the HTC could be run over by a truck and the vehicle travels through the median and hits oncoming traffic. (I think ending it past the end of the guardrail would be safer? Seems like they conflict.)

What do you think of this detail?

thanks!

From here https://www.wsdot.wa.gov/publications/manuals/fulltext/m22-01/1610.pdf

page 35.

I would agree that there may be concerns that impacting vehicles may gate through the downstream end of the HTC and pass between the two barrier systems without being redirected. That said, a fully MASH compliant design for this situation has not been developed to my knowledge.

Another complicating factor is that While you may have a TL-4 HTC, the downstream W-beam is likely not. So, a complete TL-4 system may be difficult to achieve. Thus, my comments below pertain mainly to trying to achieve this type of installation under MASH TL-3 for passenger vehicles.

In order to place these adjacent barrier systems to prevent a vehicle from being able to penetrate through the mesh point in the systems, one would need to overlap the barriers longitudinally such that a impacting vehicle gating through the end portion of the cable barrier would then impact far enough down the guardrail that the guardrail would redirect the vehicle. Additionally, one would likely want some kind of lateral offset between the barriers such that they limit vehicle interaction with both barriers at the same time. We know that W-beam can generally redirect vehicles under TL-3 impact conditions after 12.5’ into the system (ie. the beginning of length of need starts at post 3 on most end terminals).  Thus, you would need to examine the HTC you are using to determine at what point on the downstream end the cable system and end terminal allow the vehicle to gate through. This point should overlap the W-beam at least up to post no. 3.

In terms of the lateral offset, you would want to consider having a lateral offset based on the dynamic deflection of the cable barrier system in MASH testing. See the example in the Q&A response below for aa similar type of installation guidance we gave for the bullnose system adjacent to cable barrier. I think something similar would apply here.

https://mwrsf.unl.edu/q&a/view.php?id=486

Another option would be a cable to W-beam transition. There are HTC to W-beam transitions out there. However, they have not been evaluated to MASH to the best of my knowledge. We would recommend that you contact the individual high-tension system manufactures for their recommendations.

Note again that these comments are only a statement of our best engineering judgement and the current state of knowledge and have not be fully analyzed or crash tested to the MASH criteria.