警察即便在,你也能贏

you didn't violate any rules.

According to your description, there is no sign of "road closed" or they failed to show it. They (police) have to show that normal person should see it clearly.  Since it's raining, it will be difficult for them to prove that nomal person can see it clearly.

And the fact that there were  people also using that road (police acknowledged that) PROVED that normal person can't see that SIGN (if it were there) at all.

I failed to see how police has a chance in this case :).

not a lawyer.