Highway construction and maintenance worker fatalities have been on a steady decline for decades thanks to improved safety measures in and around worksites, including the use of following vehicles – also known as shadow vehicles – with truck- or trailer-mounted impact attenuators.
These highly visible vehicle buffers add another layer of protection for road and highway work crews by absorbing the impact of a crash from an errant vehicle. However, the industry has recognized that the current safety guidelines for these truck-mounted attenuators (TMA) and truck-trailer-mounted attenuators (TTMA) are outdated for today’s heavier vehicles and faster highway speeds, and new crash rating guidelines are due in 2020 (See “New TMA Guidelines Effective January 2020” sidebar). But in the meantime, industry executives offered several guidelines to consider when spec’ing a TMA or TTMA for today’s conditions.
The effectiveness of a TMA truck – its stopping power – depends on three core elements: the attenuator itself, the braking force of the TMA truck and the ballast used to increase the truck’s weight if necessary, said Samantha Schwartz-Lenhart, marketing and business development manager with TMA supplier Royal Truck & Equipment (https://royaltruckandequipment.com).
Attenuators – the actual buffers – are measured by their test level (TL) ratings. A TL-2 attenuator, for example, is qualified and tested to stop an impacting vehicle of a certain weight at a speed of 70 kmh (approximately 45 mph). A TL-3 attenuator is rated for 100 kmh (62 mph). “TL-3 is the maximum test level rating currently available on the market, and is the top tier for what is required when operating on highways where the average speed of traffic often exceeds those speed ratings,” Schwartz-Lenhart said.