Forensics of traffic signal span wires

[ACtrafficengr]

Is there any way to tell whether a signal span wire slipped through a strandvise gradually, or was forcibly pulled through it? We had an incident where a traffic signal was damaged by a hit-and-run overheight vehicle.

The signal is at the intersection of a public road and an office park driveway, and is owned by the office park. We replaced it when we reconstructed the road.

During installation, an inspector measured the height to the bottom of the lowest signal head at 16' 6". After the accident (a year later), the height was measured at 13' 6".

Since 13' 6" still puts the point of impact above legal height, it's clear to me the primary cause was the overheight vehicle.

If the spanwire slipped through the strand vise after construction, the owner could say the subcontractor was partly responsible, since the signal heads were below the MUTCD minimum. If it was pulled through during the collision, the unknown driver of the overheight vehicle should receive all the blame.

I think the owner is looking to minimize or eliminate the claim on his insurance. This is understandable, but we want to maintain good relations with contractors.

 

[Ron]

ACtrafficengr...yes, this can be determined. A microscopic examination will usually tell such by striations along the wire relative to the strand vise or clamp.

A dynamic elongation of the wire or a dynamic pull through the strand vise will show a different pattern than a slow move over time through the vise.

Would the overheight vehicle have hit the signal at its original height?

(this is not a forum I frequent, but say your post directing to this thread)

 

[msquared48]

If the hit was hard enouogh, there might even be a very slight kink in the wire where the light was when it was hit.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[sunnysky]

I read that in 1993 that the OEM , MacLean reported that certain StrandVise models did not meet 90% load specs ( specifically 5101 & 5102) , when it took over the company from Reliable.

Then again in 2000 MacLean advised against using Strandvises for ANY Challenge course particularly those designed "without automatic backup" and alternatives were strongly recommended.

Was this installation designed according to MacLean's advisory. MacLean indicate they are to be used at your own risk.

In some states the Maximum Legal height is 14ft and >14ft 6" requires a front end escort. So 13 ft 6" is an older general standard. Farm equipment is allowed up to 17ft.
Was there proper signage on clearance?