Sometimes even a gate won't stop people. I was at an afternoon baseball game at Safeco Field in Seattle the other day, and got bored, so I walked around the stadium for awhile. I stopped at a terrace on the east side of the stadium that overlooks the BNSF tracks and the grade crossing at Royal Brougham Street, where there is lots of traffic of the rail, auto and pedestrian variety. It's just to the south of King Street Station.
As I stood there, a BNSF freight approached from the south, and the bells and lights at the crossing went off, followed by the gates a few seconds later. A mobile unit for one of the radio stations was crossing just as this happened. The driver stopped, and the gate came down on the back of the van, which caused the driver to stop on the tracks in confusion or panic or something. The gate broke off and landed on the tracks.
I was horrified, thinking that there was going to be a collision - the engineer was blowing his horn, but the driver wasn't moving. Luckily, a conductor from Amtrak came running over and beat on the hood of the truck and got the guy to move, but man, was it close!
Since the gate was out of commission, they had to put a cop there for the rest of the game, but I wonder how much this happens.