2Barrier Types Roadside Barriers Median Barriers Bridge Railings Intended to shield roadside hazards, including steep slopesDesigned to be hit from one side onlyMedian BarriersPrimarily used to prevent cross-over crashesUsually symmetrical to accommodate hits on either sideBridge RailingsYou know what they are…details are in RDG Ch. 7
3Barrier Testing: NCHRP 350 (Test Level 3) STRENGTH TEST4400 lb.62 mph25 degreesSEVERITY TEST1800 lb.62 mph20 degreesTwo 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.
4NCHRP 350 Test Levels 1-3 Test Level Impact speed Vehicle Type TL-1 50 kph/30 mph820kg Car; 2000kg Pickup(1800 lb.) (4400 lb.)TL-270 kph/45 mphTL-3100 kph/62 mphRemember, 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.
5NCHRP 350 Test Levels 4-6 Test Level Impact Speed Vehicle Type TL-4 100 kph/62 mph80 kph/50 mph820kg Car; 2000kg Pickup8,000kg Single Unit Truck(18,000 lb.)TL-536,000kg Tractor Trailer(80,000 lb.)TL-636,000kg Tanker TruckTest 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 – 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.
6NCHRP 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.
7Evaluation Criteria Structural adequacy of the tested feature Occupant riskVehicle trajectory after impactBesides listing the specific number and types of tests that need to be run, NCHRP Report 350 identifies specific evaluation factors that must be satisfied.
8Barrier Structural Adequacy Any test vehicle must be contained and redirectedControlled deflection of the barrier is acceptableAny test vehicle must be contained and redirectedIn other words, all vehicles must not penetrate, under-ride or over-ride the installation, but…Controlled deflection of the barrier is acceptable
9Occupant Risk No penetration of the passenger compartment Passenger compartment should not be significantly deformedThe 1800 lb and 4400-lb test vehicles must remain upright after collisionDetached 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
10More Occupant Risks... Unrestrained Passenger Decelerations: Under 9 m/sec (30 ft./sec) preferred12 m/sec (40 ft./sec) maxOccupant deceleration over a 10 millisecond period:Should not exceed 15 G’s20 G’s is allowableThe 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)/secFollowing initial impact, occupant deceleration over a 10 millisecond period should not exceed 15 g’s, but 20 g’s is allowableFailures 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)