A total of 132 km of Interstate routes 8 and 10 in south central Arizona constitute a Dust Storm Alert System in which 40 remotely controlled signs with changeable messages alert motorists to blowing dust hazards. This system was installed because of a history of dust-related, multiple-vehicle accidents with abnormally high injury and fatality rates. Dust-related traffic accidents are caused primarily by locally derived dust blowing across the freeways during mesoscale dust storms spawned by cool air downdrafts from summer thunderstorms. These dust storms are most often spatially associated with abandoned, sparsely vegetated farm fields. As first installed, each battery-powered sign had two warning modes, one of which would be displayed depending on the severity of local dust conditions; each sign was controlled individually at a central console in response to reports from field personnel. An evaluation of this method of operation, mainly by questionnaire, showed that it was difficult to match the appropriate warning sign with fast-changing dust conditions, and motorists wanted better and more timely advice than the system was capable of providing. As a consequence, it was redesigned so that only one warning mode is now used, and all signs are activated at the same time. The warning mode cautions motorists and instructs them to tune to one of three commercial radio stations broadcasting special dust alert messages when the system is activated. Questionnaire responses suggest that the redesigned system is highly effective in alerting drivers to a general dust hazard condition. However, there are too many independent variables to determine statistically whether the system is responsible for a reduction in the frequency of dust accidents.