DataDan
Mama says he's bona fide
Most crashes between a motorcycle and a left-turning vehicle are preventable. And many can be prevented easily by maintaining speed consistent with the traffic environment.
How fast does a motorcycle have to be going to do this kind of damage? We'll probably never know. I doubt that crash investigators' momentum equations can account for a car being knocked on its side, then spun around 180 degrees while sliding. So "real frickin fast" is as close as we'll get.
One news source said simply that the westbound motorcycle (moving away from the camera) hit the Honda Civic as the car turned from eastbound to northbound (to the right in the photo). If that's all you knew about the crash it would be pretty clear-cut, wouldn't it? Driver violated the rider's right of way. But the photo--from another source--tells a different story. When a rider is going that fast--especially in a residential area with a 45mph speed limit--the law doesn't necessarily give him the right of way. As a CHP officer said when talking about speed in a different crash: "The motorcycle community's take on it is someone turned in front of them. But when speed is that excessive you give up your right of way. You can't expect people to judge your speed and location accurately when you're going 45 miles over the speed limit."
This thread isn't about the law, though, it's about preventing crashes. And--in my opinion--most crashes between a motorcycle and vehicle crossing its path can be prevented with basic skills and good judgment. The skills can be acquired with a basic MSF course and maintained with practice. Judgment, OTOH, may require you to think about traffic in new ways.
The Truth About Left-Turn Crashes
While a crash between a motorcycle and a left-turning car is almost always assumed to be the fault of the driver, the truth is that many (though not most) are caused by the rider. Of 159 fatal motorcycle crashes in the Bay Area in 2006-2007, 33 involved a car crossing the motorcycle's path, usually a left-turner, either oncoming or from a side street. Of those 33 crossing-vehicle crashes, 17 were caused by the driver, 14 by the rider, and 2 are undetermined. Among the 14 caused by the motorcyclist, the rider ran a red light or stop sign in 7 of them, and in the remaining 7 excessive speed was cited as the cause, with speed from 15 to 35mph over the limit reported. It's pretty obvious how running a red light can cause a crash, but the contribution of speed can be more subtle.
How Speed Contributes
At high speed a motorcycle becomes a danger that a driver must reckon with when it is still far down the road. In the worst case, the motorcycle is on a collision course even though it is out of sight, beyond an intervening bend or rise. The driver checks carefully, sees clear roadway, and begins his turn. But before he completes it, a motorcycle rounds the bend and collides with the car. Driver inattention has nothing to do with that kind of crash.
A speeding rider can also be in danger when the road is straight, level, and unobstructed because a driver has a limited decision horizon or span of road he checks before proceeding. He looks only as far as he must to make sure his maneuver won't interfere with traffic moving at the speed he expects to find on that road. It's an intuitive judgment, not a precisely measured one, but if a driver can safely cross 200 feet ahead of the normal 30-mph traffic, he won't worry about vehicles 300 feet away because he assumes they're moving at normal speed.
Even if a driver does see a motorcycle coming from farther away, he may not judge its speed correctly. When an object is moving straight toward an observer, the visual cue for speed is increasing size. Since a distant motorcycle is just a small point in the visual field to begin with, it doesn't grow noticeably in size until it is quite close. If it's far away, even an extremely fast-moving motorcycle is an inconsequential dot in the background.
A motorcycle's acceleration can be deceptive too. From a standing start, an aggressively accelerated motorcycle can cover ground in half the time it takes a car. A driver waiting to turn left might ignore vehicles stopped at a light a half-block ahead because they're too far away to be a threat. He expects a safe 10-second interval in which to turn, but he'll have only 5 seconds if one of them is a hard-charging motorcycle.
Finally, speed reduces a motorcycle's visibility to drivers because it decreases the time spent in a limited visual field, and that limits the chance of being seen. A driver preparing to turn may have to keep track of traffic coming in three different directions, so he's spending only one-third of his attention looking in any one direction. Traveling at 100 feet per second (70mph) a motorcyclist might not even be in the picture when a driver makes a quick glance toward him.
"Slow Down in Town"
When riding in an area where crossing traffic is a potential hazard, think about your speed and match it to the uncertainty of the environment:
Excessive speed on the part of the motorcyclist contributes to one-quarter of Bay Area fatalities in crashes with crossing vehicles, and the tactics recommended here can help prevent them. Riders running red lights account for another quarter. It should be obvious how those can be prevented. But what about the other half, where drivers are at fault? They too, are preventable--most of the time, at least. Tactics for dealing with them will be the subject of another post.
How fast does a motorcycle have to be going to do this kind of damage? We'll probably never know. I doubt that crash investigators' momentum equations can account for a car being knocked on its side, then spun around 180 degrees while sliding. So "real frickin fast" is as close as we'll get.
One news source said simply that the westbound motorcycle (moving away from the camera) hit the Honda Civic as the car turned from eastbound to northbound (to the right in the photo). If that's all you knew about the crash it would be pretty clear-cut, wouldn't it? Driver violated the rider's right of way. But the photo--from another source--tells a different story. When a rider is going that fast--especially in a residential area with a 45mph speed limit--the law doesn't necessarily give him the right of way. As a CHP officer said when talking about speed in a different crash: "The motorcycle community's take on it is someone turned in front of them. But when speed is that excessive you give up your right of way. You can't expect people to judge your speed and location accurately when you're going 45 miles over the speed limit."
This thread isn't about the law, though, it's about preventing crashes. And--in my opinion--most crashes between a motorcycle and vehicle crossing its path can be prevented with basic skills and good judgment. The skills can be acquired with a basic MSF course and maintained with practice. Judgment, OTOH, may require you to think about traffic in new ways.
The Truth About Left-Turn Crashes
While a crash between a motorcycle and a left-turning car is almost always assumed to be the fault of the driver, the truth is that many (though not most) are caused by the rider. Of 159 fatal motorcycle crashes in the Bay Area in 2006-2007, 33 involved a car crossing the motorcycle's path, usually a left-turner, either oncoming or from a side street. Of those 33 crossing-vehicle crashes, 17 were caused by the driver, 14 by the rider, and 2 are undetermined. Among the 14 caused by the motorcyclist, the rider ran a red light or stop sign in 7 of them, and in the remaining 7 excessive speed was cited as the cause, with speed from 15 to 35mph over the limit reported. It's pretty obvious how running a red light can cause a crash, but the contribution of speed can be more subtle.
How Speed Contributes
At high speed a motorcycle becomes a danger that a driver must reckon with when it is still far down the road. In the worst case, the motorcycle is on a collision course even though it is out of sight, beyond an intervening bend or rise. The driver checks carefully, sees clear roadway, and begins his turn. But before he completes it, a motorcycle rounds the bend and collides with the car. Driver inattention has nothing to do with that kind of crash.
A speeding rider can also be in danger when the road is straight, level, and unobstructed because a driver has a limited decision horizon or span of road he checks before proceeding. He looks only as far as he must to make sure his maneuver won't interfere with traffic moving at the speed he expects to find on that road. It's an intuitive judgment, not a precisely measured one, but if a driver can safely cross 200 feet ahead of the normal 30-mph traffic, he won't worry about vehicles 300 feet away because he assumes they're moving at normal speed.
Even if a driver does see a motorcycle coming from farther away, he may not judge its speed correctly. When an object is moving straight toward an observer, the visual cue for speed is increasing size. Since a distant motorcycle is just a small point in the visual field to begin with, it doesn't grow noticeably in size until it is quite close. If it's far away, even an extremely fast-moving motorcycle is an inconsequential dot in the background.
A motorcycle's acceleration can be deceptive too. From a standing start, an aggressively accelerated motorcycle can cover ground in half the time it takes a car. A driver waiting to turn left might ignore vehicles stopped at a light a half-block ahead because they're too far away to be a threat. He expects a safe 10-second interval in which to turn, but he'll have only 5 seconds if one of them is a hard-charging motorcycle.
Finally, speed reduces a motorcycle's visibility to drivers because it decreases the time spent in a limited visual field, and that limits the chance of being seen. A driver preparing to turn may have to keep track of traffic coming in three different directions, so he's spending only one-third of his attention looking in any one direction. Traveling at 100 feet per second (70mph) a motorcyclist might not even be in the picture when a driver makes a quick glance toward him.
"Slow Down in Town"
When riding in an area where crossing traffic is a potential hazard, think about your speed and match it to the uncertainty of the environment:
- Maintain speed consistent with the normal flow of traffic. When in doubt, obey the speed limit. It's often a good idea to be going slightly faster than adjacent traffic to stay out of blind spots. But if there is no adjacent traffic, that rule doesn't apply. And "slightly" doesn't mean 20mph.
- Be able to stop in the distance you can see to be clear. When rounding a bend or cresting a hill, slow down so you can stop if you happen to find a vehicle crossing your path just out of sight.
- Save the hard acceleration for open roads. Sometimes it's necessary to squirt ahead of a knot of vehicles to give yourself some breathing room, but accelerate only as hard as necessary to improve your position and don't exceed the prevailing flow of traffic.
Slowing down gives your brain a chance to notice things and more time to react. Your peripheral vision widens and you relax enough to read and predict traffic. Try walking down the supermarket aisle and reading labels, then try running down the same aisle. Now imagine all those soup cans are about to jump into your path and you'll see how slowing down affects your perception. There are plenty of places to go fast, but in and around traffic isn't one of them. If you can't slow down in town, put me in your will.
Excessive speed on the part of the motorcyclist contributes to one-quarter of Bay Area fatalities in crashes with crossing vehicles, and the tactics recommended here can help prevent them. Riders running red lights account for another quarter. It should be obvious how those can be prevented. But what about the other half, where drivers are at fault? They too, are preventable--most of the time, at least. Tactics for dealing with them will be the subject of another post.
