Spotted...

naturally a lot of people in cars driving like twats because it's raining.
no idea how it really affects them considering roof/wipers.

Was thinking just the same, the motorists behave as if they're trying not to get their vehicles too wet as if it's part of their body.

I think what actually happens is that the wet weather slows general traffic progress, so it creates more congestion which causes people to drive faster on the bits they can drive fast on out of frustration.

Notice also pedestrians becoming even more reckless in their road crossing attempts, which contributes to the general hampering of vehicular progress.