Truck stop showers are for anyone who wants to or needs to use them.
Truck stop showers are mostly used by truck drivers to shower and get cleaned up but if you're traveling by car and want to take a shower and have the money to pay for the shower you can do so.
I once had bad diarrhea on a road trip and had to change clothes and needed a shower so I stopped in at a truck stop where I paid the $10.00 fee and took my shower.
So as long as you have the money you can pay for and take a shower if you want too.
However if you can wait until you get to a hotel or motel room then you can save money because you'd be paying the hotel or motel room fee anyway.
So if I were just gonna be going to a hotel or motel and I didn't need a shower right then I would wait and shower at the hotel or motel.
But if you do need to take a shower at a truck stop you certainly can do so.