This morning, I was driving along a local state highway when I passed a trailer with the above referenced warning on it. The trailer was being towed by a TxDOT vehicle. The trailer was small with a single axle and was traveling about 50 miles per hour (in a 70mph area). A nozzle in front of the left wheel on the trailer would spray water (I presume) onto the road in front of the wheel. As promised by the warning, water would spray up from under the wheel. The resulting water patch would be about fifty feet long. Judging from the splotches of water I drove over before overtaking this machine, it had been spraying these patches of water for many miles.
What might TxDOT have been testing in this way?