If you want to go to the well, you need to turn left.

I think it's a petroleum producing area. "Well" is not the adverb. It is _not_ saying "the traffic is all well" (good). "Well" is the noun for a deep hole in the ground. There is an oil well nearby, and traffic should turn left to go to it. A "frac truck" must have something to do with the process of "fracking" or hydraulic fracturing, to increase the amount of petroleum that can be extracted. I don't know why frac trucks would not be going to the well.