Travel a long distance by car and it is likely that you will have to make at least two stops to visit the loo, or have a 'comfort break'. But where to find one when needed?
Motorway drivers have no problem, stop at a service station, but beware: you can go a long way before coming to one. On other roads, some petrol stations have loos, often in a filthy condition. The loo strategically situated in a lay-by is a vanishing species. You can always pull up at a pub, so long as the pub is open, but it is only polite to partake of refreshment which only stores up problems for you further down the road. Likewise with cafes.
It is likely you will find a loo in a town, but traffic is often directed via a loo-less ring road. Should you make it into the town centre it is likely you will be hit by parking charges, quite apart from the significant delay to your journey
My own experience is that by far the best places to head for are out-of-town supermarkets. Parking is free (usually), the loos are free, (unlike some in towns - I have vivid memories of a pay loo, with attendant to take your money, in Northallerton on a Sunday morning) and unless you have a burning desire to buy something, you can leave with your finances intact. So, before you set off on that long non-motorway journey take a look at supermarket websites and identify stopping points for that comfort break. Oh, and take some change, just in case your needs cannot wait for the supermarket.
Recently I came across an article in which the author bemoaned the fact that at some railway stations you have to pay to use the loo. Charing Cross is a pay loo, but Cannon Street, Waterloo East and London Bridge are not. Interesting that train passengers have to pay whilst supermarket, cafe and pub customers do not.