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I was contacted yesterday by FHWA about a construction project that will be bid on in February.  The FHWA had some concerns about some of the roadside safety devices being used on this project.

As I looked at the plan, I found out that the designer has developed a special detail to install steel bars to make a box culvert traversable (see attached details).  I believe that the safety pipe runner s spacing is correct.  The inside diameter of the safety pipe runners are slightly over sized.

My concerns are:

1. Does the Schedule 40 steel pipe have adequate structural strength to allow a vehicle to traverse the culvert?
2. Are the structural connections of the safety pipe runners adequate to allow a vehicle to traverse a culvert?
3. Does this detail have enough detail to be built?
4. Does MwSRF believe that this design is NCHRP 350 compliant?

I know that MwRSF tested a traversable safety runner design for a culvert.

Would it be possible to get a copy of the report (I probably have one buried somewhere in my files, but given the time frame for response, I do not know if I will have a chance to look at it).

I am not sure I have enough details from what you sent to answer all of your questions completely, but I will start with answering what I can and then we can move forward from there.

To answer the questions below:

1. The Schedule 40 pipe listed on your plans is sufficient for allowing the vehicle to transverse the culvert. The table in your plans is developed from testing done at TTI in 1980 and was later adopted as an AASHTO guideline. Furthermore, we conducted a test of the culvert pipes with the largest spacing and size in the table on a 3:1 slope with the 2000P vehicle and the 820C vehicle and found that the specified pipes and spacing were adequate.
2. I cannot fully evaluate the structural connections for the pipes from your plans. The bolt grades are not listed and no details of the culvert wall reinforcement are listed. I don't fully understand the detail for section C-C. This appears to be a detail for additional crossbars on culverts with over 20' spans. The overall details have no guidance on the location and so it is hard to evaluate. Cross bars should not be necessary on culverts with spans of 20' or less. Do you expect to install culvert grates on culverts larger than this?
3. I would add the bolt grades and the details for the cross bar installation location if necessary. Your design appears to be identical to the Iowa DOT culvert detail. There detail is more complete in terms of specifying the cross bar details and such. You may want to look at their details for further guidance.
4. If the connections for the pipes to the headwall are structurally sufficient, this design should be NCHRP 350 compliant.