Bay Area Riders Forum official Lane Splitting Guidelines

[DataDan]

What are the general recommendations for deltas when:
1. cars completely stoped
2. cars barely moving 10-20mph
3. cars moving less than speed limit 20-60

I caught myself doing a over 30 mph yesterday when cars were completely stopped on the highway. My brain didn't register it as being dangerous but once I saw the 30+ delta I slowed down a little. Generally try to stick to <20mph delta since 20 mph can be scrubbed off near instantly.

This is a dangerous underestimation. At +20mph, vehicles within 50ft (about 3 car lengths) are an immediate threat. If a vehicle 2 car-lengths ahead suddenly changes lanes, you're going to hit it. Probably not very hard, and if you go down, you probably won't be seriously injured. But you won't be able to prevent the collision.

My estimate assumes 1 second reaction and 16ft/s^2 deceleration (MSF-level braking skill--I don't know what the TCT standard is).

 

[dangerzone02]

This is a dangerous underestimation. At +20mph, vehicles within 50ft (about 3 car lengths) are an immediate threat. If a vehicle 2 car-lengths ahead suddenly changes lanes, you're going to hit it. Probably not very hard, and if you go down, you probably won't be seriously injured. But you won't be able to prevent the collision.

My estimate assumes 1 second reaction and 16ft/s^2 deceleration (MSF-level braking skill--I don't know what the TCT standard is).

20 mph is ~30ft/sec. 3 cars length, should be avoidable. <2 cars length and yeah, breaking alone probably wont save you.

Its so difficult to judge. Too bad there isn't an accurate way to test/practice a car pulling out in front of you.

 

[budman]

My advice follows the research study and that is that most accidents lane splitting occur at speeds above the speed differential (Delta between you and surrounding cars).

That extra 10MPH or whatever is providing little in terms of time saved and increases the danger greatly. Many splitting accidents occur with little space between you and a car shooting for the open gap and therefore the time and space you think you have may not be there for you.

 

[Enchanter]

Yes, 30ft per second, but it’s still going to take you 0.75-1.0sec to perceive and react.

 

[ScarySpikes]

To address the easier said than done:

"Training and practicing is essential to operating the controls smoothly which will help you overcome the tendancy to panic in emergency situations."

IOW, what you should do, how you should do it ,why you should it and the results of doing it.

:thumbup

 

[rcgldr]

"cover your brakes" - I'm able to cover the front brake with all 4 fingers, using palm, thumb, and the crotch between index finger and thumb for throttle control when lane splitting. Should I consider switching to just using 2 fingers to cover the front brake?

There was a proposed legal guideline about a year or so ago, perhaps only for southern California. It pretty much matches the guideline in the pdf file, but mentions a specific speed for freeway lane splitting, that it's only allowed if traffic is moving at 35 mph or less. It was just a proposal at the time, and looks like it wasn't followed up on. I'm wondering if anyone here has an update on this.

 

[budman]

I would use two. Practice with two in that case as well.

The official CHP guidelines are in the works. Whatever you saw was unofficial sort of like BARF's. They only have meaning if you believe they do. I believe they do.

The CHP guidelines will have a max speed in them. The Committee disagreed on what that was, but the suggested in either case was higher than the old guidelines... mostly because their is research now.

 

[Marcoose]

...filtering...

Precious.

 

[budman]

Thanks... I think your pretty cool too.

 

[DataDan]

20 mph is ~30ft/sec. 3 cars length, should be avoidable. <2 cars length and yeah, breaking alone probably wont save you.

Its so difficult to judge. Too bad there isn't an accurate way to test/practice a car pulling out in front of you.

The distance to slow by 20mph--measured in the MOVING reference frame of traffic at a steady speed of whatever--is the same as the distance to stop from 20mph, measured in the stationary frame of the earth.

So to gauge slowing distance while splitting at +20mph, first practice stopping in a parking lot, and figure out the distance you need to stop from 20mph. Add to that the distance you need to recognize what's happening and transmit the neural signal to the brake lever--I would suggest 1 second * relative speed in feet/second (20mph=29fps), but maybe you're more optimistic. Then, as you are splitting, estimate that distance ahead of you. Everything closer than that is a potential threat.

For example, if you stop from 20mph in 30ft, reaction distance plus slowing distance is 59ft. If a "car length" is 15ft, that's about 4 of them.

For a dose of reality about the danger of splitting, read the 2013 thread about Starshooter10's crash and eventual recovery.

 

[Dave H]

Filtering helps - though I hear that word in a british accent every time. :laughing

Filtering - makes me think of this silly video (from the UK):

https://youtu.be/Q29inP2m3do

Enjoy!

 

[danate]

Nice job guys!

The only thing I feel could be misleading is what you define as "lower risk." I typically find cars are more likely to make unpredictable and rapid moves in slower speed traffic (10-30mph) and generally ride with a lower delta in those situations. Higher speed certainly has a higher risk of serious injury or death, but I feel the risk of being in an accident is similar or even greater at lower speeds where rapid lane changes are more likely (this includes traffic slowing down from a higher speed).

 

[DataDan]

Its so difficult to judge. Too bad there isn't an accurate way to test/practice a car pulling out in front of you.

Instead of the estimate in my previous post, you can use this rule of thumb: While splitting, any vehicle within a 2-second range can become an immediate threat. Count it out like the 2-second rule for following distance: Spot a vehicle ahead. Guess when it's 2 seconds ahead and start counting: one-thousand one, one-thousand two. Adjust and repeat. You'll quickly learn to recognize that range and identify the vehicles that require the most attention.

Unlike a distance rule, this time rule scales up with speed (though not perfectly), and it's easy to use. Try it with KazMan's speed differential video:

Parking spaces on that street are 22 feet long, so this is how the 2-second interval translates:

[table=head]speed|spaces
10 | 1.5
15 | 2.0
20 | 2.5
25 | 3.5
30 | 4.0
[/table]

Two seconds is conservative for a 10mph speed differential, it's borderline for 30, and not applicable over 30. I assumed 1 second reaction time and 16ft/s^2 braking deceleration.

 

[anytwowilldo]

Budman, DataDan, Enchanter, Kazman. This is great information! I'm amazed we have not had more comments here yet. What I learned, and have always thought I knew, is the threat is larger than many think. Splitting with a 25 MPH or more delta can produce an unavoidable impact. We get numb to the speed or to the fact that we are covering a lot of distance quickly. I hope this gets people thinking about their delta and slows some down a bit.

 

[DataDan]

"cover your brakes" - I'm able to cover the front brake with all 4 fingers, using palm, thumb, and the crotch between index finger and thumb for throttle control when lane splitting. Should I consider switching to just using 2 fingers to cover the front brake?

You should cover the brake in traffic the same way you practice maximum braking. Basically, you're preparing for maximum braking by pre-positioning your hand.

For most riders and most current bikes, two fingers is a popular choice. But don't let someone else's preference influence your own. With practice, you'll find a position that gives you both full braking potential and smooth, precise throttle control.

There was a proposed legal guideline about a year or so ago, perhaps only for southern California. It pretty much matches the guideline in the pdf file, but mentions a specific speed for freeway lane splitting, that it's only allowed if traffic is moving at 35 mph or less. It was just a proposal at the time, and looks like it wasn't followed up on. I'm wondering if anyone here has an update on this.

At higher traffic speeds, splitting saves little time. In 25mph traffic, splitting at +15mph saves about a minute per mile. In 50mph traffic, splitting at the same speed differential saves only 15 seconds per mile.

But higher traffic speed carries greater risk. In the event of a lane-splitting crash in traffic moving at 50mph or more, you're more than twice as likely to suffer a head injury as in 20mph traffic. Same with internal injury.

More risk, less benefit in higher traffic speed. And it should go without saying that exceeding the speed limit while splitting can earn a ticket.

 

[boney]

At higher traffic speeds, splitting saves little time. In 25mph traffic, splitting at +15mph saves about a minute per mile. In 50mph traffic, splitting at the same speed differential saves only 15 seconds per mile.

But higher traffic speed carries greater risk. In the event of a lane-splitting crash in traffic moving at 50mph or more, you're more than twice as likely to suffer a head injury as in 20mph traffic. Same with internal injury.

More risk, less benefit in higher traffic speed. And it should go without saying that exceeding the speed limit while splitting can earn a ticket.

That is what investors call the "risk to reward" ratio.

In Marin County heading south it's common to catch, once past San Rafeal, the same dude that split past at 20+ delta in 50 MPH traffic, before reaching the GGB. There is no time savings and plenty of added risk. To emphasize that last point, in the past several years I've seen several of the bikes of the high-delta-high-speed riders on flat beds, and never seen them riding that bike (on the commute) again.

Perhaps some of the CMSP should be posters aimed at "high-risk" populations about dying while lane splitting at stupid speeds.

 

[ilikefood]

Instead of the estimate in my previous post, you can use this rule of thumb: While splitting, any vehicle within a 2-second range can become an immediate threat. Count it out like the 2-second rule for following distance: Spot a vehicle ahead. Guess when it's 2 seconds ahead and start counting: one-thousand one, one-thousand two. Adjust and repeat. You'll quickly learn to recognize that range and identify the vehicles that require the most attention.

Unlike a distance rule, this time rule scales up with speed (though not perfectly), and it's easy to use. Try it with KazMan's speed differential video:

Parking spaces on that street are 22 feet long, so this is how the 2-second interval translates:

[table=head]speed|spaces
10 | 1.5
15 | 2.0
20 | 2.5
25 | 3.5
30 | 4.0
[/table]

Two seconds is conservative for a 10mph speed differential, it's borderline for 30, and not applicable over 30. I assumed 1 second reaction time and 16ft/s^2 braking deceleration.

So you’re assuming 4x normal reaction time and about 1/2 maximum braking? That sounds a little too pessimistic, no? Especially with all this talk about how ABS is so awesome

I’m all for people slowing down, but there is a lot more to splitting than speed differential. There are situations where splitting at a 10 mph delta is super dangerous and other situations where a 20 mph delta is ok. And let’s not forget that nobody knows their (or others’) delta with any accuracy. So yes, let’s all slow down, but let’s not forget the importance of factors other than speed.

 

[ilikefood]

At higher traffic speeds, splitting saves little time. In 25mph traffic, splitting at +15mph saves about a minute per mile. In 50mph traffic, splitting at the same speed differential saves only 15 seconds per mile.

But higher traffic speed carries greater risk. In the event of a lane-splitting crash in traffic moving at 50mph or more, you're more than twice as likely to suffer a head injury as in 20mph traffic. Same with internal injury.

More risk, less benefit in higher traffic speed. And it should go without saying that exceeding the speed limit while splitting can earn a ticket.

Totally agree with the higher risk that comes with higher speed, but the benefit (time savings) calculation is a little simplistic because the actual time savings will depend on traffic behavior. There is often a clump of traffic that rolls slowly, so if you stay in traffic at 50 you could go at that speed for many miles, while splitting though the clump of slower traffic can get you to clear space that allows you to go much faster (and save a lot more time).

 

[budman]

I agree with the premise of finding a better space. That was part of the reason I did not want to place a suggested speed limit. The SafeTREC study showed that speeds above 50 was where danger increased a lot. Part of that is simple physics in term of motorcycle crashes.

There are times where it is beneficial to split at faster speeds. A general sense of the increasing speed led to more serious injuries in the study as one would expect. The Delta or speed differential was a great cause of crashing at all speeds. That is shown in the study. Crashing increases with higher deltas. I firmly believe this is the biggest reason to adjust your delta down.

Not everyone is a competent lane splitter even if they think they are. Your safety depends on good judgement and at times luck.

There are plenty of nuances of splitting that come to riders as they gather experience. Expectations are a key to being able to do this with greater success, but the unexpected can still happen to anyone. Applying a low delta helps keeps the unexpected more in check. If you are not a multi year seasoned commuter then the speed differential is the best way to apply the practice successfully.

People die splitting. Most motorcycle crashes don't involve another vehicle. We do it to ourselves because of various reasons. Here we have a good data based factual reason to apply a good piece of knowledge.

If you are not seasoned in the practice a lower speed differential is a valuable asset to apply, so you can become more seasoned and capable. We humans are an overconfident lot many times and that could be something that can bite you. It has bitten me before. Luckily never while splitting.

 

[DataDan]

I’m all for people slowing down, but there is a lot more to splitting than speed differential. There are situations where splitting at a 10 mph delta is super dangerous and other situations where a 20 mph delta is ok.

Exactly right. That's why we didn't place the speed differential advice in the top section about good judgment. But for a novice splitter who hasn't yet learned to identify high risk situations, speed is an important consideration, and a 10mph differential is a good place to start.

And let’s not forget that nobody knows their (or others’) delta with any accuracy. So yes, let’s all slow down, but let’s not forget the importance of factors other than speed.

Maybe you don't know your differential, but it's easy to learn. Watch KazMan's video, or just use the simple rule that one car-length in one second--one-thousand one--is +10mph (Camry-length, not F-350-length).

So you’re assuming 4x normal reaction time and about 1/2 maximum braking? That sounds a little too pessimistic, no? Especially with all this talk about how ABS is so awesome

You cannot react to a real-world lane-spitting threat in .25 seconds.

On some bikes, a pro rider on a test track with practice runs can brake from 60mph to zero at a deceleration rate as high as 1.0g. But that's the average rate from initial application--where half the bike's weight is still on the back tire--to full stop--where the back tire is just skimming the pavement. You cannot achieve that kind of deceleration at initial application. The figure I used, .5g or 16ft/s^2, is only slightly below the MSF braking skill test standard from 15mph to zero. It's what I would expect of a typical rider in a real-world situation.

ABS is awesome because it prevents crashes due to overbraking, not because it improves maximum deceleration.