May 10, 2002

> Refer to: HSA-10/B98

Terry Hopkins, PE

Traffic Congestion & Engineering Operations Unit Head

North Carolina Department of Transportation

1592 Mail Service Center

Raleigh, North Carolina 27699-1592

Dear Mr. Hopkins:

In your April 19 letter, you requested the Federal Highway
Administration's (FHWA) acceptance of the North Carolina Department of
Transportation's 3-m (10-ft) long New Jersey profile temporary concrete
barrier with a triple-loop and drop-in pin connection as a National
Cooperative Highway Research Program (NCHRP) Report 350 longitudinal
barrier at test level 3 (TL-3). Mr. Powers of my staff concurrently has
received revised copies of a Transportation Research Center (TRC) test
report dated January-April 2002 entitled "NCHRP Report 350 Test 3-11 of
the North Carolina Department of Transportation Design Portable Concrete
Barrier for FHWA Approval, Test No. 2" and videotapes of the test that
was conducted.

The tested barrier is a standard 810-mm (32-in) high New Jersey shape
portable barrier in segment lengths of 3.0 m (10 ft). The base width is
610 mm (24 in) and the barrier tapers to a 150-mm (6-in) top width.
Reinforcing consists of two longitudinal 13M (#4) bars in the barrier
stem and a u-shaped section of 6 x 6 x w2.9 welded wire fabric
throughout the barrier length. The loop connection between segments is
comprised of round 19-mm (0.75-in) diameter steel bars bent to an inside
radius of 51 mm (2.0 in). There are two such loops at the top of each
segment on one end and a single loop on the opposite end. The bottom
loops are reversed, with a single bottom loop on the end with a double
top loop and a double bottom loop on the opposite end. Barrier segments
are connected by positioning the single loops between the double loops
at each end and inserting a galvanized 32-mm (1.25-in) diameter
high-strength bolt, 660-mm (26-in) long through the all six loops. A
flat washer and nut are welded to the pin 610 mm (24 inches) up from the
bottom. No nut or other type of retention device is used on the pins.
These details are shown on the enclosure.

Twenty barrier segments were used in the test for a total installation
length of 60 m (200 ft). The test vehicle impacted the barrier at 100.4
km/h (62.4 mph) and at an angle of 25 degrees. The impact point was 1.2
m (4.0 ft) upstream from the connection between segments 7 and 8 or
approximately 19 m (62 ft) from the upstream end of the test
installation. The dynamic deflection of the barrier under these impact
conditions was reported to be 1.54 m (5.0 ft). The pickup truck was
contained and redirected, with its rear axle momentarily overriding the
barrier before it was redirected back onto the roadway. Maximum occupant
impact velocity and subsequent ridedown accelerations were 5.1 m/sec
(16.7 ft/sec) and 7.7 g's, respectively. The reported roll angle was 48
degrees. The partial override of the barrier and the relatively high
vehicular roll angle may have resulted from using a Ford F-250 pickup
truck for the test rather than the more commonly used Chevrolet C2500.
These two vehicles have significantly different suspension systems.

Based on staff recommendations, I agree that your precast New Jersey
barrier with the pin and loop connection detail described above
satisfies the evaluation criteria for an NCHRP Report 350 test level 3
(TL-3) longitudinal barrier and that it may be used on the NHS.

Sincerely yours,

(original signed by Carol H. Jacoby)

*for* A. George Ostensen

Program Manager, Safety

3 Enclosures