1. Roadside Barriers
RDG Chapter 5

2. 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

3. 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.

4. 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.

5. 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 – 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.

6. 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.

7. 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.

8. 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

9. 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

10. 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)