Connecticut Truck Mounted Attenuator - Portable Crash Cushion




FHWA approves

Connecticut Truck Mounted Attenuator

as NCHRP Report 350

TL-2 Truck Mounted Attenuator

Originally approved under NCHRP 230 in the mid 1970's.

Approved under NCHRP 350 on July 13, 1995. 

Free downloadable plans below.

CTMA as seen from the rear by motorists


In-house fabrication and repair of this highway safety system have saved taxpayers an estimated $1.3M versus commercially-available truck mounted attenuators.  The CTMA's have been in service protecting workers since the 1970's when the CTMA was first approved for use on the National Highway System.  Today, one-hundred thirty-four (134) CTMA units are in service on Connecticut highways.

Repair History for period 1999 to 200


The Federal Highway Administration (FHWA) has approved the Connecticut Truck Mounted Attenuator (CTMA) for use on the National Highway System.

The July 13, 1995 FHWA approval letter is linked to this Web page.

The ConnDOT crash test program report on the CTMA is linked to this Web page for viewing.


The CTMA consists of four 24-inch (610-mm) diameter steel cylinders supported between a steel guide frame that attaches to a shadow truck, and an aluminum impact plate assembly with aluminum channels that slide into steel tubes in the guide frame during impact.  The steel cylinders are A53 Grade B seamless steel pipe (API 5L steel pipe - oil and gas transmission line pipe, water pipe and water well casing.).  Three cylinders have 1/4-inch wall thickness and the fourth has 3/8th0inch wall thickness.


CTMA lower rail CTMA as seen from the left rear by motorists CTMA detached from truck - it's on casters!

The cylinders rest on the lower rail.

View of truck mounted attenuator. 

CTMA detaches from the truck and can be rolled about on four retractable casters.

CTMA four cylinders CTMA cylinder connection CTMA first cylinder

View of the four collapsible cylinders, which are bolted together.

Close-up of bolted connection.  Cable provides power to lights on the impact plate.

The cylinder nearest the mounting plate is cylinder number 1. 

View of retractable caster and aluminum impact plate gussets CTMA side view near aluminum impacting plate CTMA bolt connection to chasis and crank to raise/lower caster wheel

When the CTMA is detached from the truck it rolls on retractable caster wheels. 

Side view of retractable caster wheel. 

Crank for retractable caster at the chassis mounting plate.
CTMA frame attachment CTMA detached from truck - it's on casters! CTMA mounting plate

The CTMA frame attaches to the chassis beneath the truck.

The lower rail slides safely into these tubes and under the truck chassis when the attenuator is hit.

View of the CTMA frame and mounting plate 


Connecticut's one-hundred thirty-four (134) were fabricated by Department personnel in the Office of Maintenance.  The current-year cost for labor and materials to fabricate a CTMA is $5,000.  For more information, contact Charles A. Drda, P.E. [P (860) 594-2606 ]

Below are free "downloadable plans".

The CTMA meets "Test Level 2" performance requirements for truck-mounted attenuators, which were established by the Transportation Research Board [National Research Council] through the National Cooperative Highway Research Program, NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features." 

TR News Article No. 107a, "Portable Crash Cushion Saves Lives of Maintenance Crews," was published in the July-August 1983 issue.  The article provides an overview of the portable attenuator.

Photo from TRNews Article in 1983

Photo from TRNews Article in 1983

TRB Transportation Research Record 679 explains the development of the CTMA in the 1970's by Dr. John F. Carney III, then a professor at the University of Connecticut.

TRB Transportation Research Record 833 describes the original crash testing of the CTMA under NCHRP 230 standards.

Downloadable Plan Sheets for CIAS

Adobe Portable Document Format (PDF) Microstation Design File Format (DGN)
Intergraph Design File of CTMA shop fabrication details, sheet 1

PDF File of Shop Fabrication Details, Sheet 1

DGN file of Shop Fabrication Details, Sheet 1

Intergraph Design File of CTMA fabrication details, sheet 2

PDF File of Shop Fabrication Details, Sheet 2

DGN File of Shop Fabrication Details, Sheet 2

Adobe PDF of CTMA cutout pattern for aluminum sheet

Adobe PDF of cutout pattern for aluminum sheet

DGN File of cutout pattern for aluminum sheet