In the UK it’s not too hard to identify which is which, grass snakes are quick little buggers as well, although this time of year they’re readying themselves for hibernation.
You can always tell an adder, they’re quite common, and i dare say most of us into mountain biking have been within a few feet of them quite a bit over the years, you have to really upset them to get them to actually attack though, they’re quite low down the food chain though and are prey for many other wildlife, so don’t tend to stay out in the open too long, have seen some basking in the sun a couple of years ago, which i was oblivious to at the start, and probably got a little too close to 3 or 4 of them!