In downtown Fort Atkinson, WI there are explicit signs warning "Unlawful to open door into traffic", but that doesn't mean that it's unlawful to disembark via the driver's side door; it means that one must wait until there are no moving vehicles in the rightmost traffic lane before doing so (either because there are no vehicles at all there, or because they have stopped at a traffic signal).
Cops must love this one. They can hassle pretty much anyone they want, based on their judgment that the traffic was too close to the suspect. Half a block away, a block away, a mile away, etc.
Based on some of the idjits I've been stuck behind waiting for traffic to clear so they can turn, any visible or imagined traffic would suffice.