Table 1. Summary of VTMA Crash Test Results.

NCHRP Report 350 3-50 3-51
Test Designation

Vehicle mass (kg) 820 2000
Impact speed (km/h) 100.95 101.91
Impact Angle (degrees) 0 0
Vehicle impact location Nose Nose
Occupant impact velocity

(m/s)

Longitudinal 10.70 9.34
(12 max. allowable)

Lateral 1.73 0.41
(12 max. allowable)

Occupant ridedown

acceleration

(peak 10 ms avg g’s)

Longitudinal 16.53 21.48
(20 max. allowable)

Lateral 5.04 7.32

(20 max. allowable)



(Page 2 of 2)

“Crash Testing and Evaluation of the Vanderbilt Truck Mounted Attenuator” Revised 08/22/96

Wire Rope

VTMA attachment to Support Vehicle

102 mm x 78 mm x 6 mm Sox 580

5 mm thick

2D 182 mm x 152 mm x 13 mm Angles

29 mm 00 hole 25 mm doit of pin to
Cheah te tne abhor
702 mm \
oma , —_—
Boom to bed enchor
(welded to bed) RSI
Boom _ Detail

Figure 1. Details of the Vanderbilt TMA (VTMA) (continued).


@

US. Department

400 Seventh St., S.\W.
of Transportation AUG 27 1906 Washington, 0.C. 20590
Federal Highway
Administration

Refer to: HNG-14

John F. Carney, III, Ph.D., P.E.
Professor of Civil Engineering
Provost and Vice President for
Academic Affairs

Worcester Polytechnic Institute

100 Institute Road

Worcester, Massachusetts 01609-2280

Dear Dr. Carney:

Your July 22 letter requested the Federal Highway
Administration's (FHWA) acceptance of the Vanderbilt Truck
Mounted Attenuator: (VTMA) as a National Cooperative Highway
Research Program (NCHRP) Report 350 test level 3 (TL-3) crash
cushion. In support of this request, you sent copies of crash-
test videotapes and the Texas Transportation Institute's June
1996 report "Crash Testing and Evaluation of the Vanderbilt Truck
Mounted Attenuator" by Mr. Dean Alberson and Ms. Wanda Menges.
Supplemental information was provided in your August 13 letter to
FHWA's Office of Engineering.

As indicated in the enclosed drawings, the VIMA consists of four
910-mm high polyethylene cylinders of varying diameters and wall
thickness bolted to each other and to a backup structure
connected to a support vehicle (dump truck). The cantilevered
end of the TMA is supported by a cable connected to a steel boom
mounted in the bed of the dump truck and extending out over the
VTIMA at a 45 degree angle. An 890-mm square "Vehicle Grabber
Assembly" is bolted to the impact face of the VTMA. The VTMA is
3780 mm long and weighs 1158 kq.

Two NCHRP Report 350 test level 3 (TL-3) tests were reported:
Test 3-50 and test 3-51, the results of which are summarized in
Enclosure 2. The support vehicle for both tests was an 8880-kg
dump truck. For test 3-50, with the 820-kg car, this truck was
blocked to prevent forward movement. For test 3-51, it was in
second gear with its parking brake engaged. The dump truck
rolled ahead 5.4 meters after impact into the VTMA by the 2000-kg
pickup truck.


2

As noted in your letter, all the NCHRP Report 350 TL-3 evaluation
criteria were met in both tests, except the longitudinal occupant
ride down acceleration in test 3-51 which exceeded the maximun
allowable value of 20 g's by 1.48 g's. You presented an analysis
which indicated that if the impact speed had been at the low end
of the tolerances allowed,.or if the support vehicle had been
significantly lighter than the 9000-kg dump truck recommended by
the NCHRP Report 350, the 10-ms ride down acceleration would have
been below the maximum 20 g's. Although both of these statements
are valid, Report 350 suggests only a 450-kg tolerance in the
weight of the support vehicle and states that the impact severity
(IS) for a truck-mounted attenuator test should preferably meet
or exceed the nominal value. While we can agree that a
difference of only 1.48 g's may be insignificant in most cases,
we are not willing to set a precedent by accepting test values
above the NCHRP Report 350 maximums. Appendix A of the NCHRP
Report 350 states that "test results should fall below (the
"maximum" limiting values of Table 5.1] and desirably should not
exceed the "preferred" values . . ." Section A5.3 goes on the
say ". . . values in excess of the "maximum" limits are
considered to be unacceptable." Consequently, we will accept the
VTMA as an NCHRP Report 350 TL-2 attenuator based on the tests
done to date, recognizing that, with the one exception, its
performance equalled or exceeded that of TMA units that were
tested at only 70 km/h. It may be used in work zones on the
National Highway System (NHS) when such use is requested by a
highway agency. Asa proprietary device, its use on Federal-aid
highway projects, except exempt, non-NHS projects, is subject to
the conditions stated in Title 23, Code of Federal Regulations,
Section 635.411.

Sincerely yours,

Seppo I. Sillan, Acting Chief
Federal-Aid and Design Division

2 Enclosures

Geometric and Roadside Design Acceptance Letter CC-36


13 mm All-thread

29m

Bock-up Piote
jaidea to back-up structure)

19 mm Eyedort

9.9 mm Grade 80 Chain

A

Bolted to truck

wn 25, mm “|

29 mm OD holes

610 meq

T
438 mm
i

14 mm fer Graco: Assembly
vies 19 mn Eyebott ‘ste Betou’a)
Bip
29 mon Eyebott
22 mm Bolts
246 mm
an
286 mmm
120 mm
t 203 mn 7
—

Pion

Weided to tne backup plate

as fo mm x 184 mm

U-channels

Backup plate

17 mm OD holes.

Bolted to truck
with 25 mm’ bons

W405 mem «184 men

Elevation

Guck-up Stvcture

|e» rm «bm rat

|_——t90mm + 880mm + Simm Piote

Se

Figure 1. Details of the Vanderbilt TMA (VTMA).

890mm «75mm + Sm Pte

80mm 4 680mm « 9 Sm Piote
890mm 4 Témm « Gem Pate

Yam + Sim Prote

.dowenuany pero] ons] yiqepue, op JO uonenjeag pue Buse] Yse1D,,

96/77/80 Pesiacy

(2 $0 T abeq)