THey have, but that's different from actually getting the word out to people stuck in their cars. There's also the issue that many interstates have concrete dividers that make it impossible to cross easily from one side to the other. If there were a grass median, it's much easier to cross.
I'm more worried about I-45, it's always had major gridlock even in daily traffic and they do have concrete medians.
From Houston to San Antonio, Once you are west of Katy, almost all of I-10 is grass median. There of course are places you can't get across, but not many. The entire length is 2 lane service + median + 2driving and 1 shoulder + median + 2 driving + shouder + median + 2 service. In effect an 8 lane hwy + 2 shoulder lanes.