There actually is a system like this in place in Germany. Not for traffic fines, but if you get a fine in criminal court (technically your case is suspended conditionally on paying X€) it will go to a local charity.

Caused quite a bit of drama a few months ago when the "Kinderschutzbund" refused the payment in a widely publicized child pornography case (the defendant was a member of the federal parliament at the time of the crime) despite accepting it before in similar cases.