A truck-mounted attenuator (TMA) is a device that attaches to the back of a work truck to help protect work crews and the traveling public from the severe consequences of rear-end crashes between motorists and slow-moving or stopped work vehicles. Although TMAs have been used by most highway agencies and contractors for many years, there are few data on the actual in-field performance of TMAs and on reductions in crash costs attributable to their use by agencies and contractors. Such data would be useful in establishing criteria on when and where TMAs must be used. An analysis of potential rear-end crashes of motorists with work vehicles in mobile and short-duration operations found that TMAs were highly effective in reducing the severity of rear-end crashes and the costs of crashes. Each crash involving a TMA resulted in a savings of $196,855 in crash costs relative to the costs that would have been incurred had no TMA been present. On the basis of current TMA prices, agencies can recoup the cost of the TMA in terms of reduced rear-end crash costs in less than a year of daytime work shifts on facilities serving 20,000 vehicles per day or more and of nighttime work shifts on facilities serving 50,000 vehicles per day or more.