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Cable Barrier Heights

Question
State WI
Description Text

We have a number of resurfacing project near previously installed cable barriers.

These project likely will change the cable height of the proprietary systems being used. 

Does MwRSF know of acceptable variation in height for proprietary systems?

Does MwRSF know of acceptable modification to existing proprietary systems to get the cables at the appropriate height?

Has MwRSF had similar conversations with other states about this topic?


Thanks

Keywords
Other Keywords cable barrier
Date October 1, 2015


Response
Response Our current experience with development and testing of the non-proprietary, high-tension cable median barrier for the Midwest Pooled Fund has shown that cable median barriers can be sensitive to cable heights along with other factors. With respect to overlays, the greatest concern would lie with override of the cable barrier system. As the overlay increases the height of the roadway with respect to the barrier, the potential for the vehicle to impact higher relative to the cable locations increases and thus increases the potential for vehicle capture to be compromised and override the barrier. Additionally, the cable interaction and interlock height with respect to the vehicle will be affected even if the vehicle is captured which could promote increased vehicle instability.

We are not able to directly comment on specific proprietary cable barrier systems and what level of overlay they may be able to tolerate as these systems vary in cable height, cable position on the post, cable attachment to the post, and other factors. Additionally, testing of the Midwest cable median barrier system has largely been conducted to MASH according rather than NCHRP 350. But in a general sense, one would expect that the additional of a pavement overlay would degrade vehicle capture and increase the potential for barrier override and vehicle instability.

In terms of retrofitting the existing cable barrier systems, there is not simple answer. There may be potential means for adjusting the height of the cables in these systems without a complete re-install, but it is largely system dependent. A simple lifting of the post is not likely a good solution as this would raise all of the cable heights and may degrade vehicle capture and barrier performance for backside impacts or low angle hits that compress the vehicle suspension and cause the vehicle to engage the lower cables on the system. Similarly, retrofits that increased the height of the top cable to compensate for the overlay might help with override mitigation, but the increase in the cable spacing on the post could increase the potential for vehicle penetration. 

At this time, MwRSF does not know of any acceptable height tolerances and/or potential retrofits for cable barrier systems to compensate for overlays. However, as noted above, there are concerns with the effects on barrier performance, and it seems be be a topic worthy of further consideration. 


Date October 1, 2015


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