Missouri law (section 304.022.2) requires that drivers–on roads with two or more lanes in each direction–upon approaching a stopped emergency vehicle with flashing lights shall move over into a lane away from the emergency vehicle. The exception is where changing lanes is unsafe or impossible; then the driver must slow down.
This is the law as written and as enforced by the Missouri Highway patrol. So if you can move over, but you don’t, then you get a ticket. Slowing down is not an option–IF you could have moved over.
Defense attorneys, however, are challenging those tickets because of these brilliantly executed signs which have been erected on our state highways:
Imagine the driver, upon being ticketed for not moving over, complaining, “But I slowed down!”
It’s true, ignorance of the law is no excuse, but it’s a bit of a dirty trick to get bad legal advice from the highway department (I presume) and then a ticket from the highway patrol. Somebody goofed.