Bicycle Safety - The Math of Speed

[DrkAngel]

I'm not arguing for or against speed, but I should point out that your math only allows for hit-from-behind accidents. Only about 1 in 7 are of that type; most are right-hooks, left crosses, or cars coming out of a side street.

Good point! Let's compare:
Biker at 10 mph vs 20 mph in a 30 mph traffic situation.

Per mile - 10 mph biker will be:

1. passed by 4x (times) as many vehicles =
a. 4x the possibility of hit, or swipe x (2x impact speed)
b. 4x the possibility of "right cross" **

2. 2x the volume of oncoming traffic =
a. 2x the possibility of "left cross" **
b. 2x possibility of head on x (.8 impact speed)
(30 + 10 mph vs 30 + 20 mph = 80% impact speed)

3. 2x the volume of cross traffic, sidestreets, driveways etc. =
a. 2x the possibility of cross traffic collision **
Twice as long, being a target, in the intersections!

Note: Actual percentages listed where available. Other impacts are highly variable due to possible angle and bike into vehicle or vehicle into bike.

** Speed, or severity, of impact will vary, from 50% to 100% (possibly higher).

Best case is 50% impact speed of 10 mph biker into side of vehicle.

Worst case would be, side impact of biker by car, 100% impact speed. Possibility of being "run over" might be 2x, for the 10 mph biker. (Momentum of 20 mph biker is much more likely to carry him past the car = much greater chance of not being under car!)***

(Same direction impact already established at 4x possibility & 200% speed-severity.)

*** 20 mph Biker possibility of impact is approx. 25% to 50% that of the 10 mph Biker.
Additionally, 20 mph Biker is 2x as likely to strike the vehicle while the 10 mph Biker is 2x as likely to be struck by vehicle. (Applicable to all, except same direction & head-on!) Possibility of 10 mph Biker going under vehicle is MUCH greater!

The final, measurable, variable might be, "time to see", (tts), the biker. (10 mph biker) While following traffic only has .5x the tts, oncoming traffic has 1.25x the tts, and the cross traffic has 2x the tts.

The additional factor of faster motion being more noticeable, especially in the peripheral vision area, should be added, but, I'm afraid, assigning percentages would be sheer speculation.

(Peripheral vision is much more attuned to detecting motion, as well as light, especially flashing light. Another good reason for a "strobe" headlight, during the day.)


Personally, I believe, faster still looks a whole lot better-safer.

 

[docnjoj]

Hmmm....I like the octopus suit but I'm not convinced by the speed argument. I would be concerned about avoiding stationary objects, car doors opening and pedestrians. Remember when we were "supposed" to drive at 55 mph? Traffic fatalities went down quite a bit. I see your arguments but still will remain a tricycle rider at bicycle speeds on the streets. Picking a safe route seems to be the best way to stay alive to me.
otherDoc

 

[liveforphysics]

I ride the same pace in traffic and around town on my Ebike as I ride on my GSXR1000 or any other motorcycle. Motorcycle brake, motorcycle tire, better acceleration than 95% of cars, and a 90mph top speed. But soo much better than a motorcycle. Like a million times better.

 

[LI-ghtcycle]

now some fact from my side :

I drove 11 000 km on ebikes since 2007.

average speed 25-30mph
max speed 112kmh

max speed in trafic 45mph

Accident with car: ZERO

accident on dirt in the forest : .. two.. was moderate...



We also must specify THE ACCELERATION !!

On my side i'm 100% convinced that with a resonable skilled ebike driver, aceleration decrease the risk of accident!

When you are on the front of all cars when they all start from a stop.. that avoid you to being hit by a car that is turning on that intersection!!.. while normal cyclist are stand up on the pedal to try accelerate slowly na dhave more chance to be hit by car that want to turn!

In my case, it bnever happen.. Once the light turn to greeen, i'm far away from the cars that start acelerate behing me!

believe me... Acceleration is safer than speed :wink:

Doc

I agree, it's the acceleration and situational awareness that keep you safe more than anything, however, depending on where I ride still determines the "safe" speed more than anything.

I also live in Oregon City which seems to be half retirement community, half young families, so bad combo! More than once going 25-30 MPH in the bike lane along a busy street has caused me to nearly get left crossed by in-attentive drivers, however when I am able, I keep up with traffic going the same speed as the cars (30-40 MPH going down the big hill here in town, I take the road like any other vehicle) but if I'm not careful, even riding along a street with a bike lane with all the signs indicating it as a bicycle route, I can still get into trouble.

I also agree if you're riding on the shoulder of a 55 MPH rural road is dangerous at best, and by far better if you are able to keep up with traffic.

I ride on a regular basis on the bike path/shoulder of a 40 MPH busy highway, but I just watch traffic, and that is also why I have a mirror to watch traffic behind me too.

I have been on some really bad rural roads that have a ditch rather than a shoulder, and had to "ninja bicycle" when someone wasn't paying attention and go into the ditch to avoid being hit from behind.

Sad thing is it's about 50/50 weather they are running me off on purpose or because they aren't paying attention, I have had people make the comment "I'm aiming for your if your in the way" because other bicyclists have ticked them off being a$$-hats and made them frustrated, and of course there are those who run even other cars off the road if they are in a hurry/bad mood.

I'd love to build up a high speed E-Bike next that can be capable of motorcycle speeds just for safety's sake, but most of the time I'd just be using the superior acceleration to keep a good safety bubble between me and traffic.

 

[docnjoj]

Hey LFP! How about designing and building a commercially availible bike or dare I say it, trike or Velo with those abilities! You have the ability and it would be a boon to those of us who would rather get rid of of cars but still be able to get places. I'm serious!
otherDoc

Edit: Dammit! We need a spell checker!

 

[DrkAngel]

DrkAngel,

It's been a while since I've seen such a well done and amusing put-on as the "Octopi" cycle wear post. But take care or you'll have some fools start practicing for your extreme sport. (g)

Thanks, I put some work into it.

Almost as amusing as the "fools" on a different forum, who chastised me for promoting a dangerous product.
I had to laugh at the poor soul, who claimed that the Consumer Product Safety Commission would ban this item!

Honestly, I tried to make it clear that this was a joke.

I began as plausible, but continued to increase the ... outrageousness, till ... absolutely no one could possibly think it was anything but a joke.

Or so I thought ...

I did add the disclaimer, just in case ...

Impact From Behind - Best Scenario & Solution!

 

[dogman dan]

Actually, if you are about to be hit, and have no options, like a cement wall instead of a ditch to dive into, getting hit square on and surfing the hood may be your best bet. I've surfed a hood, and came up fine. So if you can aim for hood, do so, rather than get crushed between a wall and a truck.

I totally agree about having acceleration being good. I totally agree that getting into the flow of traffic, then using cars as your blocker can be really good.

There is just too many variables for you to say faster is better and leave it there. It depends on the road, the rider, the bike. I can't say I'd be as comfy on LFP's bike as he is. But I bet I'd ride it a lot faster than my bikes. 8) My bikes tend to have weak frames, vbrakes and cheap tires. My commuters would probobaly scare lots of folks over 25 mph.

Beating the horse some more, the real safety is whatever it is that keeps you from getting hit. Mostly it's really good situational awareness. Mostly people have real poor situational awareness, that's why you don't trust em when they drive a car near you.

 

[wineboyrider]

Actually, if you are about to be hit, and have no options, like a cement wall instead of a ditch to dive into, getting hit square on and surfing the hood may be your best bet. I've surfed a hood, and came up fine. So if you can aim for hood, do so, rather than get crushed between a wall and a truck.

I totally agree about having acceleration being good. I totally agree that getting into the flow of traffic, then using cars as your blocker can be really good.

There is just too many variables for you to say faster is better and leave it there. It depends on the road, the rider, the bike. I can't say I'd be as comfy on LFP's bike as he is. But I bet I'd ride it a lot faster than my bikes. 8) My bikes tend to have weak frames, vbrakes and cheap tires. My commuters would probobaly scare lots of folks over 25 mph.

Beating the horse some more, the real safety is whatever it is that keeps you from getting hit. Mostly it's really good situational awareness. Mostly people have real poor situational awareness, that's why you don't trust em when they drive a car near you.

Yep! When you going to come ride with me in the mountains!?

 

[DrkAngel]

Acceleration is a good thing!
But ... even the most powerful bike, can't match acceleration, to my deceleration.
In, less than 2 seconds, about 1 car length, I can go from 20 mph, to a clean stop.
Going from 20, to 30mph, might take, 5x, that time and distance.
Contrary to the insistence, of a certain persistent moron, you can practice a "panic" stop!
(He went over the bar ... twice. Once in front of a menacing dog, Once, in front of an approaching car.)

It is important to become familiar with your braking capability!
It seems, more feasible, to maintain "escape speed" and be able to lose it quickly, than to ride slower and rely on, a much delayed, acceleration. ... ?

After 10,000+ eBike miles, (16,000+km), I've found, well maintained, brakes to be my best friend.
They have saved me, and various pedestrians, several times.
I began a "religious" attention, to brake maintenance, immediately after a "lapse", prompted me, to acquire some fairly persistent, joint injuries, rather than run into a newbie, child biker.
I "jackknifed" my front wheel and dove over a small biker, who decided to pull a U-turn, in front of me.

 

[dogman dan]

No kidding. At any speed good brakes are good. And knowing how to get the most out of em is gooder.

The reality though, is that the vast majority of ebikes are going to have crap brakes, and for them approaching 30 mph is pretty sketchy. I tend to have average brakes, and feel ok up to 25 mph, but I definitely need a lot more room to stop by 30 mph. Just because of gearing and liking to pedal, I tend to go 20-25 mph. At least I'm a pretty good bike mechanic, and keep cheap brakes adjusted right.

When acceleration helps is the situation where you just screwed up royal, and put yourself in danger. Only getting gone is going to save you now, so floor it an pray. See it coming, and you have time to brake, and not be there in the intersection or driveway about to get hit. So by far, I prefer not needing acceleration to save me. Most riders just use acceleration to get through a smaller hole. I'm old, and more patient now, and don't mind riding a bit slow or waiting a bit to go.

 

[DrkAngel]

After 10,000+ eBike miles, (16,000+km), I've found, well maintained, brakes to be my best friend.

I'm Sorry!
I apologize!

I have a few best friends!

1. Speed - reduces the amount of traffic that I encounter
2. Wide to zoom LED headlight - Strobe during day, gets me noticed. Bright at night, lets me see.
3. Brakes - tested daily, adjusted very often
4. Tail-turn lights - gets me noticed + signals my intentions
5. Helmet gear -
a. Nice, wide view mirror
b. Velcroed helmet-mounted wide-zoom LED light, zoomed, to see further, at night + zoomed strobe during day - I look toward people who might not notice me
c. Rear, 5 led, red flashy light - no excuse, not to see me!

Speed reduces the volume of trouble, that I can get into.
Strobe light gets me seen & respected, I can tell if I forgot to turn it on, by how traffic treats me!
Brakes, help keep me out of trouble, or reduce the severity of my mistakes.
Tail-turn lights, get me noticed and inform others of my, "responsible" actions.
My helmet mounted wide mirror keeps me well informed of side & rear traffic, with a slight eye movement, a slight head turn even lets me see right side traffic!
Zoomed, helmet mounted light lets me spot potholes ahead, and see around curves, strobe mode will wake up the most comatose driver!

Remember ... you can never have too many friends!

 

[John in CR]

If you're really interested in safety then don't ride at night. Half of bicycle fatalities occur after dark when the number of riders is many times lower and kids on bikes (also half of fatalities) are even less. Half of those night fatalities have some lights, so don't think lighting is enough. If it's unavoidable, then of course light up well.

Also, if brake maintenance is high, you should try both regen braking, which greatly reduces the work done by your mechanical brakes, and switching to hydraulic brakes, which don't need adjusting. Fiddling with brakes drove me crazy. Now I'm getting over 6 months out of a set of pads, so reducing brake maintenance to twice a year is heaven for me. Plus regen braking eliminates brake fade, so my brakes are always ready for maximum braking force, unlike before I had regen when care was needed on downhill grades, especially when taking a highway exit immediately after or during a downhill grade.

 

[gensem]

DrkAngel do mind to elaborate on brands/models of the gears that you use, specialy thoses

Wide to zoom LED headlight
Tail-turn lights
Nice, wide view mirror

 

[DrkAngel]

DrkAngel do mind to elaborate on brands/models of the gears that you use, specialy thoses

Wide to zoom LED headlight
Tail-turn lights
Nice, wide view mirror

Headgear

http://endless-sphere.com/forums/viewtopic.php?f=3&t=26860&start=15#p426034
Items:
200 lumen Wide-Zoom High-Low-Strobe $7.99 shipped!

Bicycle Bike Turn Signal Brake LED Light +8 Tune Horn - $8.99 shipped
Horn is ornamental. - I also have air horn.
Brake switch might restrict cable! - I don't use.
I upgraded the LEDs!

Zefal Spin Mirror- $6.84 free ship w/$25 order
Do not mount mirror on bar! - almost useless! Mount on helmet visor! See "Headgear" link - above. Maintain 4"+ from eye - to prevent focus problem.

 

[dogman dan]

Yeah, I pretty much gave up night riding after hitting that dummy walking along in all black. For me it's convenient enough to do that, I ride in the dark only in the early morning. Now I just wait for enough glow to see a guy in black. Then flash various lights hoping to be seen. While relying on seeing them first.

 

[DrkAngel]

Just found a great LED light!
Overrated? (Lumens), but extremely bright & efficient!
2 hours on high, 4 hours strobe, 4 hours medium, 24+ hours on low, from 1 - 2600ah Li-ion 18650.

"Buy it now" - $30 - $40, but auctions typically go for $20 - $25. Some bundled w/batteries & charger.
1300 Lumen Cree XM-L

1800 Lumen Cree XM-L

New - Brighter , better selection and price - Bicycle XML lighting!

 

[dogman dan]

If you ride at night, good lights help a lot. When I hit that dope in black, I thought I could see far enough, but couldn't for riding fast.

Faster you go the better light you need. Multiple lights are a good thing. I can't see anything being too many. Led's that flash on the tire valve are great for side visibility, and I really liked a helmet mounted light so I could give that guy in a car at a stop sign the look. See me now? bet you can't see anything now, but now you know I'm there you hugger.

 

[itchynackers]

That looks like a great light. I purchased this setup... http://endless-sphere.com/forums/viewtopic.php?f=3&t=21227
It was way better than I expected. I have just one of these, and in complete darkness, I can see clearly all the way down to the end of the block (about 200 yards). It has a nice smooth, wide visibility. Not the cheapest, but after I bought it, I was glad I spent the money.

 

[The Mighty Volt]

A car can't hit a biker that isn't there. When you have 2800w on tap, not being there is just a half-twist away.

 

[dogman dan]

That's why those dopes sitting at a stop sign wait till you are nearly there, paying attention to thier cell phone, then lunge out into your path without looking when it's to late for you to do shit about it. A little blinding light in thier eyes from your head mount light does the trick. Hey A----- here I am! Flasher lights up front help the same way. I flash a light in my morning commute, even though it's daylight by then.

 

[999zip999]

I went to Tucson the speed limit is 15mph at the school zone with 2- 4way stop signs took 20min's because there was no GO sign.

 

[dogman dan]

Beats the standard here, go without looking. At stop signs, as I roll past in the morning on the non stop frontage road, all I see is people looking at thier laps while they text. Then they roll, then they look. 8)

I saw a new bike commuter on the frontage road last week. New comfort bike, riding with a shiny new yellow shirt on. Rides up to an all way stop intersection with three cars that just stopped. He looks at all three of us one by one, and rolls right through.

We need a mandatory bicycle riding class as the first step in the punishment when a guy gets his DUI. :lol:

 

[DrkAngel]

I just re-found a representation of collision rate vs speed differential.



Collision rate would appear to be 20-25% for the 20mph cyclist vs the 10mph cyclist, in a 30mph traffic environment.

 

[MadRhino]

This shows that if you ride at traffic speed, you are less likely to have an accident.
It also shows that riding slower than average traffic speed is more dangerous than riding faster.

 

[DrkAngel]

Fall = Impact speed - analogy

"A fall off a 3.3 feet desk results in a speed at impact of 10 m.p.h.
A 10 m.p.h. change in speed (Delta-V) in a motor vehicle collision is equivalent to falling off a desk.
Similarly,
a 15 m.p.h. change in speed is equivalent to falling 7.5 feet - off a step ladder.
A 20 m.p.h. change in speed is equivalent to falling 13.4 feet - off the roof of a one story building.
A 25 m.p.h. change in speed is equivalent to falling 20.5 feet - off a two-story building.
A 30 m.p.h. change in speed is equivalent to falling 30 feet - off a three-story building."

A very relateable impact speed analogy - scientific numbers.