FWIW, we drove up SR1 from Morro Bay to Salinas this week, and I was surprised to see only low-band antennas on every Caltrans Truck I saw. (And we saw a LOT of their vehicles). Almost all the cars (supervisors?) had NO antenna on them, with the exception of a broadcast antenna. I saw no sign of the usual gain 800Mc Antennas or even the 2" spike. I wish I had read this thread earlier, as we only had the 800Mc freqs programmed in the scanner, and heard nothing on them. Did put in 47.18 on the rest of the trip back down SR25 from Hollister, and nothing heard on that one either.
The good news is that the drive up SR1 was free of any delays, and the weather was glorious.