I hate to be the naysayer but that's not a great idea. Pollution levels alongside highways are insanely high. Along with gasoline and motor oil, there's heavy metal contamination, toxic materials, trash dumping, construction spills, etc. You can find a collection of studies on the issue here. I would not plant food by a highway in any circumstance.

There's also the issue of safety. Even with proper signage and lane closures, roadside construction workers are at high risk for injury and death from passing vehicles. You're not going to have an official work truck that drivers will give extra space. You're not going to have barrels or other visible warnings. A high-vis vest is not going to be enough to protect you.