First down! Lane split 101N in SF

[firewatch]

First off, it's been about 15 hours since the incident, and I'm not feeling any real injuries. Had some sensitivity around the back of my left ribs, and my left knee (which is already crappy) feels aggravated. No bruising anywhere.

Gear: Shoei RF-1200, Alpinestars leather jacket, Bilt Trophy leather gloves, Bilt Iron Workers jeans, Alpinestars Tech 5 MX boots

All except the helmet made some contact with the ground. Tech 5 boots probably saved me from a world of hurt, as the bike landed RIGHT on my leg, and I felt the Astars logo sliding on the pavement. This is literally the reason I normally commute with MX boots! Jacket has no visible damage, jeans have two small holes where I carry my flashlight in the left rear pocket, gloves barely scraped as I pretty much just held onto the bars until my sliding speed was low.

What happened: splitting between lanes 1 and 2 on 101 North around 9:30am, probably a delta of 20mph. Fiat changes lanes as traffic was slowing ahead, and spends a decent amount of time slowing in between the lanes. While braking my front tire contacted the rear bumper, maybe just hard enough to pop some plastic rivets off, and sent my rear tire around my right side, low siding in the far left lane at maybe 15mph. Only slid for a few yards, maybe.

My mistakes identified so far:
Delta. I may have been as fast as 40mph, and traffic in that section may have slowed to 10mph, leaving up to a 30mph delta. I believe it was more like 20mph delta, as that's where I feel comfortable, but I could have been going faster. Truthfully, I was tired of the changes in speed so I wasn't on top of it. I wasn't being a dumbass on purpose
Better rear brake control. I started to slide almost immediately, and let it keep sliding to avoid a high side. Because the rear tire was already sliding it ensured that I went down when my tire tapped the bumper.
Target fixation. I found myself looking at the rear bumper as I got closer, while I probably could have swerved right. This is debatable, as the rear tire was already sliding to the right. Had I tried to swerve right I may have high sided. (or would I?) Then we circle back to brake control! Neverending loop!

Afterwards: The driver of the truck behind me stopped quickly and even pulled over to give me his business card. The Fiat driver also stopped and we exchanged phone numbers and license info. Both have replied and everything seems fine. Don't think I'll bother with filing a claim, as it was an honest mistake of her not realizing that traffic was slowing while she changes lanes. The reason for such a slow down was a previous traffic accident, about 100 yards ahead. The left lane was blocked, so it kind of explains the situation.

[bmwbob51]

Too fast and lay off the rear brake! Lesson learned.

[DataDan]

Originally Posted by firewatch

My mistakes identified so far:

The mistake you have not identified is spotting the gap in traffic into which the Fiat merged and recognizing it as an immediate danger. The most common lane-splitting crash by far is the one you had: the lane-change cut-off. Actively look for lane-change opportunities and when you see one, adjust accordingly: SLOW DOWN and be ready to brake. Lower speed differential gives you two advantages: If the driver is checking his mirror for splitters (big IF), you are more likely to be seen, and if he does initiate a move into the gap, you will be able to slow in less distance.

Delta. I may have been as fast as 40mph, and traffic in that section may have slowed to 10mph, leaving up to a 30mph delta. I believe it was more like 20mph delta, as that's where I feel comfortable, but I could have been going faster. Truthfully, I was tired of the changes in speed so I wasn't on top of it. I wasn't being a dumbass on purpose

Vulnerability to a lane-change cut-off increases with speed differential as shown in this graph:



At +20mph over the slower lane--you are vulnerable out to 3 car-lengths. If a vehicle 3 car-lengths ahead begins to cross the corridor, you will not be able to avoid it. You're gonna crash. By slowing to +5 in that situation, you have a much better chance to avoid a collision in the event of a lane change--at 1 car-length you should be able to slow in time.

Learn to accurately estimate differential. And remember that the relevant speed is relative to the SLOWER of the two lanes. If one lane is faster and has a gap, the threat is from the slower lane. You will need to slow to that speed in the event of an incursion.

The easiest way to judge speed differential is to count out one second as you overtake a typical car (not a truck). Approaching an Accord or a Camry or whatever, begin counting as you pass the rear bumper: "One thousand one". If you reach the front bumper as you finish the last syllable, you're doing +10mph.

Kazman's video shows how speed differental looks:

edit: the vimeo embed is apparently not working. Watch here: https://vimeo.com/135403669.

[Enchanter]

Great post Dan. You're a huge asset to BARF.

[ScottRNelson]

It appears that you've already figured out what you did wrong. The last time I crashed - 15 years ago - it took me months to come up with a good theory for what exactly I did wrong.

This is a good reminder to me about watching speed differences. I can't legally split lanes where I live now, so that isn't an issue, but being in a lane next to traffic that is going significantly slower is still a concern. You have to be in a position where you can avoid lane changers that don't see you and invade your space. If you can't move over another lane that means reducing speed to where you don't have one of those tall red columns in DataDan's chart.

By the way, I would also like to thank DataDan for an excellent post.

[firewatch]

Thanks for all the input, especially the metrics.

Very soon into riding (started this past Dec) I did the same visual estimation of lane splitting speed, using parked cars as markers. That's how I decided I was uncomfortable above 20mph, and will smoothly decrease throttle.

The driver that saw it happen wrote back to me, saying that the Fiat made a late timing choice to change lanes, and got stuck slowing down in the corridor, which just confirms what I thought happened, and why it wasn't possible for me to slow enough. I asked if he thought I was going fast, but he said that there wasn't much I could do. This is all just opinion, and doesn't change what happened. It still comes down to me not anticipating it.

Future changes:

More conservative delta and more conscious of maintaining it when traffic slows down even more

Avoid the rear brake until I have the front suspension settled, and feather it lighter

Going back to looking at side mirrors - this is what I did at the beginning, and while riding bicycles. I'd ensure that I have at least two seconds with which the driver could peek and see me coming up before I get to a single car length behind them. This is provided that they even check

More left-to-right movement with high beam on to draw attention...again, if their mirrors are adjusted properly

Most importantly: exercise more patience. I've had times when I caught myself riding too aggressive, and thought up a few "what if" scenarios. Then I dial it down. Lane splitting already gets us there faster, so there's no need to add an extra rush.

[berth]

Originally Posted by DataDan

The mistake you have not identified is spotting the gap in traffic into which the Fiat merged and recognizing it as an immediate danger.

The other thing to consider also is simply cars the size of Fiats, which are particularly small and short, can move very quickly from lane to. More so than, say, an Accord, or and SUV.

Mini's also fall into that category. Very quick and nimble and potentially will jump into smaller gaps that what you may consider normally for cars.

[WorldSBK]

Very glad to hear you are fine.