The Practical Guide to Truck-Mounted Attenuators

Everything a fleet manager needs to understand about TMAs in one place: how they work, what the ratings mean, deployment basics, and how to keep a unit legal.

A truck-mounted attenuator, or TMA, is a crash truck that shields a work crew from traffic. It parks behind the work area as a shadow vehicle, and if a driver runs into the closed lane, the attenuator absorbs the impact and steers the vehicle away from the cab's coffin corner. This guide covers what you need to know to buy, run, and maintain one.

Ratings and standards

MASH 2016 is the current crash-test standard; it replaced NCHRP 350. Test levels tell you where a unit belongs. TL-2 suits work zones at 45 mph or below. TL-3 is required at 50 mph and up, and those units are crash-tested at roughly 62 mph. Every compliant attenuator carries an FHWA Hardware Eligibility Letter tied to its specific model.

Deployment and daily use

• Deploys from travel position to protect in about 20 seconds.
• Rated to run at up to 50 mph while positioned behind a moving operation.
• Transfers between trucks in around 10 minutes, so one attenuator can serve several trucks.
• Optional testing to 70 mph is available for higher-speed applications.

Keeping it legal

The truck plus payload should sit at roughly 26,000 lb GVWR or more to prevent underride. And watch the calendar: non-MASH-2016 attenuators built before January 1, 2023 have to be off the road by January 1, 2030. If your unit predates the standard, plan the replacement now rather than scrambling later.

How is a TMA different from a fixed crash cushion?

A crash cushion is bolted to the ground at a fixed hazard. A TMA is mounted on a truck so it can shadow a mobile or short-duration operation wherever the crew works.

Can one attenuator move between our trucks?

Yes. A transfer takes about ten minutes, so many fleets buy fewer attenuators than trucks and move the unit to wherever it is needed.