Bicycle Safety - The Math of Speed

[ZOMGVTEK]

It really just depends on where you ride. I tend to ride on the shoulder of the road, and most roads on my way to work have ample space. However, drivers entering or exiting side streets and businesses are less likely to see me if I am traveling fast, so I tend to go about 20 MPH. At that speed, most people see me, and recognize me as a bicycle. When I'm going 40 in the middle of the road, I have a lot of people pulling out right in front of me. I prefer to ride 30 MPH in 30 zones, following a car. The car in front of me cant really present much of an issue for me, and people tend to get out of the way. The vast majority of the time, people also give me ample following distance when I ride in traffic at higher speeds. Nobody is likely to pull out between two cars, regardless if they see me or not, and I dont have to worry about people passing me.

Basically, I ride with traffic at 30-40 when there is no shoulder, and ride as far over as possible at 18-22 MPH when there is.

[dogman]

You guys have seen what I have. At some point, your speed changes the hazard from bike type hazards to motorcycle type hazards.

The right and left crossing traffic that either didn't see you, or expected you to be going 12 mph definitely increases. Somewhere around 30 mph, you aren't going to stop in time anymore, no matter how good your brakes are. Now you are in motorcycle territory, where your survival depends on being capable of choosing the place you crash. Slide off the side of that car, or smack into the hood. Choose the slide if you can.

Again, the single most effective thing you can do, is ride a safer route, even if its a few miles longer. My route has all kinds of little safe cuts in it. Avoiding a few big intersections, detouring around a 1/2 mile section of dangerous 4 lane street by taking to the parking lots. etc. Of course, on the back streets the speed limit is 25 mph. I have a section of route where I could travel fast safely, and go 30 mph. Few driveways, and no left crosses on a on way street. 30 is ok with me, its the limit for mopeds in my state.

[DrkAngel]

Open Road Edition

I've demonstrated how faster is safer, in a 30 mph traffic environment. But "On the road", with higher speed traffic, is where the most concern about passing vehicles exists. How does speed effect your risk in a 60 mph traffic situation.
First, let me qualify;
1. Riding is in an rural area and 95% of the roads are 55 mph limit.
2. I ride on the right side of the road, going "with traffic", as is the legal method.

For ease of math - Let's figure a 10 mile trip, w/traffic @ 10 cars per minute.

60 mph traffic:

At 10 mph -
60min x 10cars - 1/6 (for 1/6 speed of cars) = 500 cars passing you at 50mph.
Driver has 7 seconds to notice & accommodate biker.

At 15 mph -
40min x 10cars - 1/4 (for 1/4 speed of cars) = 300 cars passing you at 45mph.

At 20 mph -
30min x 10cars - 1/3 (for 1/3 speed of cars) = 200 cars passing you at 40mph.
Driver has 9.5 seconds to notice & accommodate biker. Cars have approx. 1.4 times the time to notice, and avoid, you! (vs 10 mph).

At 25 mph -
24min x 10 cars - 5/12 (for 5/12 speed of cars) = 140 cars passing you at 35mph.

At 30 mph -
20min x 10cars - 1/2 (for 1/2 speed of cars) = 100 cars passing you at 30 mph!
Driver has 12 seconds to notice & accommodate biker.

(Math is simplified - but "sound")

When you consider that, in "open road" conditions, most bike collisions are directly related to passing cars, then 20 mph would be (2.5 times safer than 10 mph) x (1.4, the time the, approaching, driver has to see biker) = nearly 4 times safer @ 20 mph, compared to 10 mph!

30 mph would be (5 times safer than 10 mph) x (2, the time the, approaching, driver has to see biker) = 10 times safer @ 30 mph, compared to 10 mph!

Note: Some of the math is approximated, fairly accurate, but will modify if deemed necessary.

Most impressive is that every bit of speed increase greatly reduces the volume of passing traffic and therefore increases the safety factor!

A__hole factor! Everyone might agree that, possibly, 1 in 100 motorists are AHs toward bicyclists, (Conservative Estimate!), Going 10 mph you'll get passed by 5, only 1 @ 30 mph.

[dogman]

Couldn't agree with you more, for more rural riding where the right and left cross opportunites are few.

In that situation, for sure going faster can be safest. Texting mofo might even look up soon enough to see you. But what is really key, is it gives you more time to do your endo into the ditch avoiding having him tag you.

On the other hand, I much perefer doing my riding the bike off the road and into the ditch much slower. At 15-20 mph, I might even avoid going over the bars. I've been run into the ditch at 50 mph, while descending a big hill. Pretty sure it was deliberate by the driver. Watched him swerve at me to run me off the pavement. Riding off into the ditch at 50 mph was,,,, entertaining. Might even say stimulating. A nice ditch I didn't crash ,but wow that frame was bending like rubber.

Which brings me to the other thing. No car, or truck, EVER passes me that I didn't eyball the sob. That way the relative speed of the car doesn't matter. No way I'm allowing it for him to hit me. NO WAY. But for sure, when you ride faster, you buy a potentially life saving extra few milliseconds for you to dodge for the ditch. Definitely a pain in the rump to eyball 300 cars an hour, but whatever the number, you must eyball every single one.

We get a few bike fatalities every year localy. Nearly always the situation you describe, 45 or more speed limit, driver hits the bike from behind. In a way, always partly the riders fault. Didn't eyeball that driver and take evasive action.

Does trusting drivers not to be drunk, texting, spilling the coffe etc make sense? hell no.

[scotticeberg]

Getting hit sucks. I don't ever want to do that again.

Sometimes I take the ENTIRE lane. Sometimes I take the sidewalk. Sometimes I ride the wrong way down the road(not often). It all depends where I am riding.
Whatever keeps me safest. It's an art.

In San Diego taking the lane, or taking the sidewalk, all depended if I was traveling uphill, or downhill. Sometimes there were bike lanes. Downhill I might hit 40mph. Uphill, in some places, I was off the bike and walking.

In Detroit it is whatever goes. More towards the city there are enough under utilized side-streets that I have the road all to my self. Out in the suburbs its an anything goes 'Mad Maxesquean' gauntlet of sidewalks that stop and start at random, bike/ped paths that make no sense, and motorists who rarely see a cyclist, and act like it.

We have some nice rail-trails here in Michigan, not really practical for commuting purposes, however.

We need a national bike highway system....so I can go fast, and rarely have to worry about getting creamed by some moron in a car/truck/bus/semi.

[DrkAngel]

Any direct impact by a car will, (almost), instantly accelerate a biker to, (very near), the vehicle speed, regardless of biker speed, or direction.

Math based on rear impact, at various speeds

C=Car
B=Biker
"Result" is the, post impact, resulting speed for car & biker both.

3000lb C (30mph) vs 150lb B (stationary) = 30mph impact = 28.5mph result
Initial impact comparable to fall from roof of 3 story building, onto hard car
Damage=probable broken bones, severe internal & head injuries etc.

3000lb C (30mph) vs 150lb B (10mph) = 20mph impact = 29mph result
Initial impact comparable to fall from roof of 2 story building.
Damage=possible breaks, internal injuries, concussion etc.

3000lb C (30mph) vs 150lb B (20mph) = 10mph impact = 29.5mph result
Initial impact comparable to fall from roof of 1 story building.
Damage=possible sprains, bruises etc.

3000lb car @30mph could be completely stopped by head on collision with 150lb biker @600mph, (near Mach1)!

Sorry, ... got carried away by math, it can be fun, ... maybe not for that biker tho ...

[Doctorbass]

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

Doc

[DrkAngel]

Absolutely the best solution to a rear impact scenario requires good speed capability, constant awareness, and one piece of specialty equipment.

First you want to be traveling, as closely as possible, to the speed of the approaching vehicle.

Second you must have an awareness as to the velocity, angle, mass and surface composition of the vehicle. Sets of 4 mirrors, or more, recommended, if possible, arrange into a stereoscopic, full 3D configuration.

Thirdly, and most importantly, the one piece of specialty equipment! "Cyclists Downunder", (based, possibly, in Australia?), has begun marketing their "Octopi" line of cyclewear.

Just make sure that you are struck squarely from behind. If you are about to be hit, quickly swerve and position yourself directly towards the center of the vehicle, the car should knock the bicycle from under you and you should roll gracefully onto the hood and, or, windshield, where the Octopi suction cups should keep you safely secured. (Tip: As soon as you get stuck to the vehicle, rip off one, or both windshield wipers! Some drivers will use them to try to knock you off. You can also beat them on the roof to get the drivers attention, in case he is sleeping, or just doesn't notice you.) Hopefully the car will come to a gentle stop and you can then safely get off. Much safer than rolling down the road at 30 mph or bouncing over the roof and landing, "who knows where"! (Tip: Please do not anger, or insult, the driver! You will probably need their help getting unstuck from the car!)

Warning! Speed is important! 20 mph bike speed is optimal to be hit by a 30 mph car.
Slower can result in fairly severe injuries.
Faster and you might not be bounced onto the top of the car, you might have to jump backwards, timing is critical! Warning! Be careful, some a__hole drivers will approach like they are going to hit you, then ... slow down, just before impact. If not aware you might jump, and miss, ... then where would you be? ... Embarrassed! ... ???

Large trucks can be very tricky. Most don't have a nice hood to get stuck to.
1. Ideally, you must be going 10 mph slower than the truck.
2. Timing is critical, you must jump straight up just as you are being run over.
3. You must hit the windshield squarely, with enough body, to stick. Grills-radiators don't work well with suction cups!

This is a skill! Like any skill it requires practice. You should have a friend try to run you down, a few times, just so you can get good at being safer.

Oh, ... Make sure you have a good supply of bikes handy.


P.S. Be prepared for being hit by the, proverbial, "Redneck Pickup". Keep an Armageddon bag handy, on your bike. Recommend couple bottles of water, sun screen, some granola bars, "Space blanket" ... anything you might need in case they drive around with you stuck to their hood, for a few days.

Disclaimer! You must read "Epitaphs of the Downunder Cyclists", before attempting this "solution"!!!

[Uncle Ron]

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)

[Uncle Ron]

I have found that when riding my bike at +30mph the average car driver and pedestrian isn't expecting you to be travelling that quick and they pull out in front of you. Then there is a surprised look on there face as you almost run up there ass. If you were riding a motorbike people expect it to be Doing 40mph + and give you space.

I feel its great to have a bike that can do 40mph with strong acceleration. But riding at 20mph would be safer and just use the power to get you out of a dangerous situation.

Kurt,

A most sensible post that I heartily concur with! On the other hand there have been lots of sensible posts on this thread that are well worth heading, particularly in how to deal with various types of riding situations. It always a combo of safety/speed/acceleration. Best to have all three if you can, but to always remember that speed can kill and maim whether with e-bike alone or in crossing paths with another vehicle. Dogman's "eyes on the idiots" is most appropriate, because it keeps your mind in the safety game and may give you that extra split second that's the difference.

[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

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]

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. 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. 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]

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]

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.