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TL-2 Combination Rails

Question
State WI
Description Text Do you know of any TL-2 combination railings that are crash tested?

We have a municipality that wants to place a TL-2 combination railing about 2’ behind vertical curb on a 25 mph roadway.

I was asked to come up with some alternatives that are similar to what they propose and other alternatives (i.e. no barrier, move barrier face to curb face…).

Thanks,
Keywords
  • Bridge Rails
Other Keywords none
Date December 5, 2014


Response
Response

I don’t know of any test TL-2 combination bridge rails offhand.

 

We have done or have seen related research in the past that Illinois is currently using.

 

In 1998, the MwRSF developed and full-scale crash tested a combination traffic / bicycle bridge railing to TL-4 of NCHRP Report No. 350. The bicycle railing consisted of steel posts and rail segments mounted to a 32-in. tall New Jersey shaped concrete barrier. The barrier system utilized steel cables strung through the longitudinal rail elements to retain fractured railing segments during severe impact events. However, during crash testing, numerous spindles were broken free from the larger longitudinal tubes.

 

Another research effort was conducted regarding pedestrian railings for Missouri Department of Transportation. Two combination traffic/bicycle bridge railings with horizontal, tubular steel rails for use on a rigid, single-slope, concrete barrier were designed, constructed, and full-scale vehicle crash tested according to NCHRP Report No. 350. The first test consisted of a 2,015-kg (4,442-lb) 1998 GMC C2500 pickup truck impacting at an angle of 25.6 degrees and at a speed of 101.5 km/h (63.1 mph). The pickup snagged on the longitudinal rails during climb and eventually rolled, resulting in test failure. For the second test, modifications were made to the system in an attempt to reduce vehicle penetration and prevent rolling. The second test was also conducted with a 1998 GMC C2500 pickup truck. The pickup weighed 2,029 kg (4,473 lbs), and impacted the system at an angle of 25.6 degrees and at a speed of 102.7 km/h (63.8 mph). Once again, the pickup snagged as it climbed the barrier, resulting in vehicle roll and unsatisfactory results. The results indicated that the barrier system is not suitable for use on Federal-aid highways. However, it was noted that modifications could be made to the system in order to increase its chances of successfully meeting the requirements specified by NCHRP Report No. 350. One change was the use of an increased lateral offset for positioning the posts and rail farther away from the back side of the concrete barrier.

 

In 2013, the Illinois DOT began to develop a parapet-mounted bicycle railing system. Although Illinois DOT initially sought to utilize the barrier previously developed by MwRSF, concerns about the steel cables and vertical spindles led them to develop a new railing design based that combined the two combination traffic/bicycle rail systems described previously. The new design eliminated both the cables and the spindles while still satisfying AASHTO, FHWA, and Illinois specifications for bicycle and pedestrian railings. The steel rails were mounted and offset from the back of the parapet such that the rail faces were positioned 13-in. away from the front-top corner of the concrete parapet. Since this offset is greater than the Zone of Intrusion for TL-2 concrete barriers, MwRSF recommended its implementation as a TL-2 barrier without full-scale crash testing.

 

TTI has done several other TL-2 bridge rail tests, but I don’t have all of the details for those. You may want to check the TF 13 bridge rail site and the 2006 FHWA bridge rail book (red).

http://www.aashtotf13.org/Bridge-Rail.php

http://guides.roadsafellc.com/bridgeRailGuide/index.php?action=view&railing=78

 

Let me know if you anything else.

Date December 8, 2014
Attachment Bicycle Railing-Parapet Mounted.pdf


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