SAN ANTONIO -

On Sunday, San Antonio police Officer Jonathan Esquivel was critically injured when he was struck by a vehicle while working an accident scene on Loop 410.

The accident brought attention to a law on the books since 2004 -- drivers in the lane next to emergency vehicles have two choices: slow down or move over.

"If no lane is available for you to vacate to, then you need to slow down 20 miles an hour below the speed limit,” said San Antonio police Officer Marcus Trujillo.

The law applies to police, fire, EMS and tow trucks.

"Folks really need to pay attention (and) be on the lookout for emergency lights (and) emergency vehicles because we are trying to make it safer for everybody out there," Trujillo said.

The law just doesn’t apply to highways -- it also applies to roadways and school zones.

"Where the speed limit is already reduced to 20 miles an hour and you see flashing lights, in cases like that, you need to slow down to five miles an hour," Trujillo said.

Since the accident involving Esquivel, Chief William McManus said he has seen a change.

"I have come across several emergency vehicles pulled over to the side of the road -- police and ambulances -- and (motorists) are making a wide birth,” said McManus. "Apparently, that message is out there right now and I am glad of it."