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Minimum Concrete Barrier Lengths

Question
State	NM
Description Text	I work for NMDOT. We are in the process of completing a project to upgrade guardrail along Interstate 40 to MASH standards. It is my understanding that NMDOT requires all concrete wall barrier along the Interstate to meet TL-4 criteria and must be a minimum of 42” in height. However, we cannot locate any information correlating the length for a 42” permanent concrete wall to meet TL-4 criteria. The only information our general office could locate was a test where a 120’ long 42” CWB met the TL-4 criteria. Based on this information, the general office is requiring the minimum length of a 42” CWB to be 120’ long. This is a very expensive CWB and, as you can imagine, is eating up our project budget very quickly. Do you have any testing information or guidance that you can provide NMDOT that indicates a shorter length of 42” CWB will meet MASH standards? This information would be greatly appreciated.

Question

State

Description Text

I work for NMDOT. We are in the process of completing a project to upgrade guardrail along Interstate 40 to MASH standards. It is my understanding that NMDOT requires all concrete wall barrier along the Interstate to meet TL-4 criteria and must be a minimum of 42” in height. However, we cannot locate any information correlating the length for a 42” permanent concrete wall to meet TL-4 criteria. The only information our general office could locate was a test where a 120’ long 42” CWB met the TL-4 criteria. Based on this information, the general office is requiring the minimum length of a 42” CWB to be 120’ long. This is a very expensive CWB and, as you can imagine, is eating up our project budget very quickly.

Do you have any testing information or guidance that you can provide NMDOT that indicates a shorter length of 42” CWB will meet MASH standards? This information would be greatly appreciated.

System Performance Evaluation

System Types
Permanent Concrete Barriers

Applications

System Features

Date March 19, 2019
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Response
Response (active)	To answer your question on the minimum length for a concrete barrier to meet TL-4 criteria, it all depends on what you want it to do. When we conduct crash testing to TL-4, we typically utilize a 100-150 ft long system to ensure the vehicle box has adequate time (system length) to stabilize following the impact event. After initial impact, the vehicle typically rolls toward the system and leans on the barrier. If the barrier is too short, the vehicle will continue to roll and may eventually rollover. A shorter system length may be able to contain a TL-4 single unit truck, but the stability and trajectory of the vehicle after impact is unknown. Also, system lengths are typically calculated using run-out lengths to ensure the barrier extend far enough upstream of the hazard to prevent arrant vehicles from getting behind the barrier and impacting the hazard. You may want to consider this before selecting a very short barrier length.

Response

Response
(active)

To answer your question on the minimum length for a concrete barrier to meet TL-4 criteria, it all depends on what you want it to do. When we conduct crash testing to TL-4, we typically utilize a 100-150 ft long system to ensure the vehicle box has adequate time (system length) to stabilize following the impact event. After initial impact, the vehicle typically rolls toward the system and leans on the barrier. If the barrier is too short, the vehicle will continue to roll and may eventually rollover. A shorter system length may be able to contain a TL-4 single unit truck, but the stability and trajectory of the vehicle after impact is unknown.

Also, system lengths are typically calculated using run-out lengths to ensure the barrier extend far enough upstream of the hazard to prevent arrant vehicles from getting behind the barrier and impacting the hazard. You may want to consider this before selecting a very short barrier length.

Date April 22, 2019
Previous Views (198) Favorites (0)