Not sure if this was addressed earlier. If it was, let me know.
With that behind, I suggest icing on roads to form as a result of freezing temperatures after a rain or fog. I'm pretty sure there's a grip mechanic regarding tires so shouldn't be hard to implement (hopefully, I'm not a dev). This would add a bit more realism and challenge to driving a car. Imagine just casually driving and then losing control which ends with a glorious crash.
Well technically even water on a road should decrease the grip in some way. Dirt roads could get muddy as well, slowing a car down.
What is your opinion on this suggestion?