I passed a line of cars and was just about to enter an intersection with the green light when a van made a left turn in front of me from the far right lane (parking lane). There's a dedicated left turn lane at that light, plus two thru lanes and then the parking lane on the far right. I was caught off guard because it happened really fast and I wasn't anticipating that person to cut across 3 lanes to make a left. I reefed on the front brakes but also managed to lock up the rear - I think the skid started on the white cross walk/stop line paint. Once the rear wheel starts to slide it doesn't have much stopping power and the bike will start to fishtail as you try to steer. Get enough sideways motion and you'll either lowside, or let off the rear and as the bike straightens up - highside.
Just scraped by the van. My main goal was to reduce the force of impact if that happened (and steer left to avoid the impact). I was mostly curious who was driving the van. It was a young kid - he felt really bad, motorcycle rider himself and just didn't see me. I think he was late for something at the Community College and had been looking at a map or something and saw the line of cars a 1/2 block or so behind me and figured he could zip across the intersection no problem.
Reminded me once again how important it is to drive defensively, scan ahead for possible hazards, practice quick stops/swerves, concentrate on using the front brake and staged/progressive braking.
That's the third near miss I've had in the last several years. One where a guy on a cell phone ran a red light and the other when two girls stopped their car in the road on a blind spot on a curve in Mt. Rainier National Park. They were looking at something...I locked up the rear wheel on the Sportster that time too. It's a really ? sinking feeling to feel a bike start to fishtail - because you can't tell right away how bad it will get.
There are two theories on what to do if you lock up you rear wheel - one is to keep it locked up which may mean you will put the bike down but at least on a low side rather than going up and over. I think keeping the rear wheel in a skid is a bad idea unless the bike is moving in a straight line when the skid starts...and even then it doesn't make sense to me because of the decreased braking action of a skidding tire. The other is to keep your eyes focused where you want the bike to go, let the rear wheel skid if it starts and release the rear brake - assuming the front and rear wheels aren't too far out of line - if they are the natural tendency of the wheels to line up once the rear starts spinning again, may cause the bike to snap up and over and for you to go over the top.
Ideally you don't lock up either wheel and don't get into situations where you have to do emergency stops.
From HowStuffWorks "Motorcycle Riding" -
"Both brakes should be used at the same time, although the front brakes are more powerful and will typically provide 70 to 90 percent of the total braking force. New riders often fear using the front brake, but it should be applied every time a motorcycle is slowed or stopped. Many accidents are caused by riders braking incorrectly. According to the California Highway patrol, locking up the rear brakes is a factor in the majority of motorcycle crashes."