Turn signals have been standard equipment on automobiles since the late 1920s, but not all drivers use them like they should.
"(Blinkers are) your way of communicating with the traffic around you," said San Antonio police Officer Marcus Trujillo. "If you don't use your turn signals, no one knows when you intend to change lanes."
Signaling that you are about to change lanes or make a turn is not only considerate of other drivers, it cuts down on accidents -- not to mention it's the law.
"You want to give the drivers behind you sufficient warning so they can start slowing down ... because you don't want a chain-reaction accident to happen behind you," Trujillo said.
But just because you use your blinker doesn't mean you can be a bully about it, Trujillo said.
"That doesn't give you carte blanche just to go ahead and bull-doze over (other people)," Trujillo said.
You must give ample warning.
There are also rules for those drivers who like to zip across several lanes of traffic at once.
You have to travel at least 100 feet before you can make a lane change. The stripes on the road will help you make that maneuver.
"All lanes are marked with stripes," Trujillo said. "The spaces between the stripes are 30 feet long, the stripes themselves are 10 feet long, so if you take the gap plus the strip, that's 40 feet, so once you have three sets of those, you have passed 120 feet."
Trujillo said an illegal lane changes could cost you $150 in fines.