We don't have this information, and plant dieback along highways can be caused by a range of factors, like herbicide applications (either by a utility or an agency targeting invasive species, perhaps) or vehicle fires or disabled vehicles or hot construction vehicles parked overnight (especially during this drought and high heat). These are only guesses, and we can't determine from the images what the cause here was. You could ask county government or the State Highway Administration, depending on who is responsible for managing the right-of-way along those roads. We've seen similar, highly-localized vegetation dieback situations this summer along other roads in other counties, especially in areas with road work.

Miri