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One of KDOT’s field offices is asking for some guidance for placing a sign similar to the one shown in the JPG behind a w-beam bullnose end terminal. The sign would be mounted on breakaway bases. Although there are some smaller advisory speed signs at this location today, the SB to EB loop is still experiencing larger vehicle (WB-67) rollovers where the drivers are approaching this interchange at too high of a speed. The location of the end terminal is shown in the attached Google Earth KMZ file. It’s my understanding the w-beam bullnose system was last evaluated under NCHRP 153 criteria. The distance from the nose of the end terminal to the opening between the two bridge structures is 229’. I wasn’t sure what the appropriate guidance would be for placing a large sign, similar to the attached picture, relative to the nose of the end terminal. Is there any information/guidance you might be able to provide for my consideration? Is there any reliable information available that might suggest how far into the system we might anticipate a vehicle to travel if it struck the w-beam end terminal on the nose? The posted speed for through traffic travelling SB is 65 mph.

If there’s other information needed to help with providing some guidance please let me know. I believe our field office was needing something back by Wednesday February 27th so they could order the sign to be fabricated if this is how we are going to proceed. If the recommendation is not to place the sign behind the w-beam bullnose end terminal that’s also acceptable. I’ve already suggested to them placing the sign on the west side of the SB lanes as an alternative.

Thanks

I can provide some guidance on your situation. The W-beam bullnose described below was likely based on a Minnesota W-beam bullnose that was tested to NCHRP 153 or a later version that was tested a SwRI to NCHRP 230. The system tested at SwRI never met all of the crash tests.

Regardless of which system it is, it is unlikely that the W-beam bullnose will meet MASH or NCHRP 350 due to issues with vehicle capture and occupant risk.

That said, the thrie beam bullnose developed through the Midwest Pooled Fund should provide some guidance on the sign placement. NCHRP 350 and MASH testing of these systems have had maximum capture lengths of around 55’-60’, and we have recommended a longitudinal offset of approximately 65’ from the nose of the system to objects inside the system. While we can’t guarantee that the W-beam system would have the same capture distance, we can assume that it would be in that range if the vehicle were to be contained. If we add an additional 50% to that distance to account for potential performance differences, it would result in an offset of 100’. I would think that would be a reasonable placement estimate.

Note that there would be lateral offset concerns as well. I would make sure that the lateral offset follows our current MGS working width guidance.

That would be our best recommendation at this time. Again, this assumes that the W-beam bullnose would contain the vehicle, which is not a given under our updated impact criteria.

Let me know if you need anything else.

Thanks