Roadside Barriers RDG Chapter 5

Barrier Types Roadside Barriers Median Barriers Bridge Railings Intended to shield roadside hazards, including steep slopes Designed to be hit from one side only Median Barriers Primarily used to prevent cross-over crashes Usually symmetrical to accommodate hits on either side Bridge Railings You know what they are…details are in RDG Ch. 7

Barrier Testing: NCHRP 350 (Test Level 3) STRENGTH TEST 4400 lb. 62 mph 25 degrees SEVERITY TEST 1800 lb. 62 mph 20 degrees Two tests are needed for barriers at TL-3 -- a strength test and a severity test. The strength test is used to determine if the barrier is tough enough to prevent penetration by the pickup truck, and the occupant severity test is used to determine if the resultant crash is “gentle” enough to minimize harm to vehicle occupants. The next two slides show the tests required for each of the 6 test levels for barriers. The pickup is used to represent the pickup, vans, SUV, minivans, etc.

NCHRP 350 Test Levels 1-3 Test Level Impact speed Vehicle Type TL-1 50 kph/30 mph 820kg Car; 2000kg Pickup (1800 lb.) (4400 lb.) TL-2 70 kph/45 mph TL-3 100 kph/62 mph Remember, in all these tests the 820-kg car impacts the barrier at 20 degrees and the pickup truck at 25 degrees. The only difference between these three test levels are the impact speeds. TL-3, at 100 km/h, is the standard test level for most high speed roadways.

NCHRP 350 Test Levels 4-6 Test Level Impact Speed Vehicle Type TL-4 100 kph/62 mph 80 kph/50 mph 820kg Car; 2000kg Pickup 8,000kg Single Unit Truck (18,000 lb.) TL-5 36,000kg Tractor Trailer (80,000 lb.) TL-6 36,000kg Tanker Truck Test levels 4 through 6 include the two tests with the small car and the pickup truck, but add an 18,000 pound panel truck and 80,000 pound tractor-trailers to the mix. These larger truck tests are all run at a 15 degree impact angle. NCHRP 350 is currently being updated – 2005-2006 it should be completed. Dual units used, no other significant changes. 62mph – TL3 vs. 75 mph speed limit – no good data on crash speeds – we assume that the drivers slow down a lot. And cost benefit of 62 to 75mph is minimal.

NCHRP 350 Test Levels 4-6 TL-4 Vehicle TL-5 Vehicle TL-6 Vehicle This is what the 4, 5 and 6 level trucks look like. Note the higher rail under the tank (TL6) that must be contained.

Evaluation Criteria Structural adequacy of the tested feature Occupant risk Vehicle trajectory after impact Besides listing the specific number and types of tests that need to be run, NCHRP Report 350 identifies specific evaluation factors that must be satisfied.

Barrier Structural Adequacy Any test vehicle must be contained and redirected Controlled deflection of the barrier is acceptable Any test vehicle must be contained and redirected In other words, all vehicles must not penetrate, under-ride or over-ride the installation, but… Controlled deflection of the barrier is acceptable

Occupant Risk No penetration of the passenger compartment Passenger compartment should not be significantly deformed The 1800 lb and 4400-lb test vehicles must remain upright after collision Detached fragments from the test article should not penetrate the passenger compartment of the test vehicle nor should the passenger compartment be significantly deformed. 6” max penetration. All occupants considered, including those in the rear. The 820-kg and 2000-kg test vehicles must remain upright after collision

More Occupant Risks... Unrestrained Passenger Decelerations: Under 9 m/sec (30 ft./sec) preferred 12 m/sec (40 ft./sec) max Occupant deceleration over a 10 millisecond period: Should not exceed 15 G’s 20 G’s is allowable The theoretical speed at which an unrestrained passenger strikes the interior of a rapidly-slowing vehicle should be under 9 m (30 ft)/sec, but may be as high as 12 m (40 ft)/sec Following initial impact, occupant deceleration over a 10 millisecond period should not exceed 15 g’s, but 20 g’s is allowable Failures more often for longitudinal: rollover, they don’t contain, or passenger compartment intrusion. Failures for head-on (crash cushion) – most often excessive deceleration (too stiff design)