# Advocacy & Safety - Bicycle Safety - The Math of Speed

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

Pages : [1] 2

DrkAngel
07-13-13, 07:02 AM
Faster is Safer!
My Sister-in-Law just can't understand, why I feel that going faster, on a bicycle, is safer. "30 mph!" ... "You're gonna kill your self!". ...

I feel it necessary to prove that, up to the speed of surrounding traffic, faster is safer. Let me try a mathematical approach.

First, let me qualify;
1. My riding is in an urban area and 95% of the streets-roads are 30 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.

30 mph traffic:

At 10 mph -
60min x 10cars - 1/3 (for 1/3 speed of cars) = 400 cars passing you at 20mph.

At 15 mph -
40min x 10cars - 1/2 (for 1/2 speed of cars) = 200 cars passing you at 15mph.

At 20 mph -
30min x 10cars - 2/3 (for 2/3 speed of cars) = 100 cars passing you at 10mph.
AND, cars have twice the time to notice, and avoid, you! (vs 10 mph).

At 25 mph -
24min x 10 cars -5/6 (for 5/6 speed of cars) = 40 cars passing you at 5mph.

At 30 mph -
20min x 10cars - 3/3 (for 3/3 speed of cars) = 0 cars passing you!

(Math is simplified - but "sound")

When you consider that many bike accidents are directly related to passing cars, especially in a "road" environment, then 20 mph would be (4 times safer than 10 mph) x (2 - twice the time the, approaching, driver has to see biker) = 8 times safer @ 20 mph, compared to 10 mph!

Most impressive is that each speed increase of 5 mph reduces the volume of passing traffic by 50%!

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 4, only 1 @ 20 mph and at 30 mph you might never encounter 1.

EBikeFL
07-13-13, 07:51 AM
DrkAngel, I agree with you that going faster is safer. However, I've noticed cars don't like the idea of a bicycle either maintaining their same speed and/or catching up to them at the stop lights.

Imagine if you're in a car and see a cyclist maintaining speed with you. You probably start wondering why am I paying for gas, car payments, insurance, etc. when this cyclist is going to get to the same destination about the same time as me. It's like watching someone get a 50% discount when you just paid full price. It would make you upset and angry.

When you ride your bicycle at 30 mph you remind car drivers they just paid full price.

There is the other issue of reminding car drivers that gas prices are only going to go up and that they are stuck with being a forced consumer. Eventually, they will entertain the idea of riding a bicycle and that probably frightens them too.

The positive car drivers will actually see a light at the end of the tunnel witnessing you travel at 30 mph. I've always believed that traveling at 30 mph conveys to the driver that there are other transportation methods besides a car. They no longer see the bicycle as just a fun recreational activity but more of a legitimate form of transportation.

Many car drivers want to ditch their vehicles but they just don't know what other options are out there. When they see me carrying groceries and traveling at 30 mph it's like a light has come on in their head.

turbo1889
07-13-13, 07:56 AM
Provided you don't wipe out - Yes, speed to keep up with traffic is good and helps earn you some respect. The same is true with a pedal only bike by the way. I can break above 20-mph for short spurts on my pedal only "bus bike" (ride the bus with the bike in the rack between towns and then ride the bike around town) and doing so really helps with safety and getting a little more respect when I ride around town in traffic riding "All In" technique center of lane and holding my position in the traffic cue like I was a motorcycle in stop and go 25-mph speed limit square grid traffic patterns.

Now when it comes to wiping out - speed is your enemy even more then weight since weight is linear to kinetic energy in a wreck where as velocity is exponential to the square. Wipe out at 20-mph instead of 10-mph and you hit with four times the kinetic energy, wipe out at 30-mph instead of 10-mph and you hit with nine times the kinetic energy.

Shimagnolo
07-13-13, 08:06 AM
To be specific, energy in a moving object: 0.5 x mass x velocity^2

But I agree with the OP that I feel safer when my speed is closer to that of motor vehicles.

turbo1889
07-13-13, 08:22 AM
My point is the faster you go, the more carefully you need to ride because the harder you go down if you go down.

As to keeping up with traffic actually ticking off some drivers, that is usually only the case if you filter up, if you don't filter up at the reds and stops and instead hold your position in the traffic cue it won't make as many drivers mad and actually make a lot of them respect you more when they see that you can keep up with them and hold your own.

If you filter up and as a result you are either making better time then they are and getting further and further ahead of them at every light or worse yet they have to pass you over and over again (yes in the mental state of 99% of all car drivers when it comes to a bicycle in the road ahead of them they do have to pass even if it is in the middle of a block between stop lights and they know your just going to filter up again), now that is what gets them ticked off. They will blame you for constantly getting in their way and it just about makes them go critical mass nuclear with a lot of dirty fallout.

Long story short, if your moving fast enough to keep up with traffic, don't wipe out, and hold your position in the cue at the reds and stops rather then filter up because doing so can make some drivers go nuclear on you when they end up passing you multiple times and more then minus out any safety gains you may have made by keeping up with traffic better with more speed. Now if you can make good enough time to outrun them altogether, then it is worth considering filtering up but use some discretion on that as well.

Jimi77
07-13-13, 10:04 AM
Interesting way to think about it. Maybe I'll start looking at 2kw motor again. :p

Watchdog
07-13-13, 10:35 AM
Well I don't think you can assume that by going 30 mph no one is going to pass you. If you assume there are some a_hole's out there, then they'll certainly pass you at 30 mph. EBikeFL kind of touches on it. If someone is an a_hole and sees a bike going 30 mph they might be upset and pass you dangerously to prove a point.

But I do agree with you that keeping up with traffic makes an aspect of riding safer. On my route to work I often take a different route in one section than the route I take coming home. The reason? Going to work the one street that's a more direct route is uphill (about 3% to 4% grade) on a narrow road and I don't want to be going 15 to 20 km/hr up this road with traffic stuck behind me getting pissed off. But going home it's downhill and with the slight downhill I can easily go over 40 km/hr and I find traffic doesn't mind being behind me for the one block stretch the road is narrow. No one ever honks or tries to pass, and I move over as soon as the road widens.

Jimi77
07-13-13, 12:15 PM
Well I don't think you can assume that by going 30 mph no one is going to pass you. If you assume there are some a_hole's out there, then they'll certainly pass you at 30 mph. EBikeFL kind of touches on it. If someone is an a_hole and sees a bike going 30 mph they might be upset and pass you dangerously to prove a point.

For some reason, I suspect that a_hole is going to pass dangerously whether you're doing 10mph or 30mph. :notamused:

EBikeFL
07-13-13, 12:28 PM
Well I don't think you can assume that by going 30 mph no one is going to pass you. If you assume there are some a_hole's out there, then they'll certainly pass you at 30 mph. EBikeFL kind of touches on it. If someone is an a_hole and sees a bike going 30 mph they might be upset and pass you dangerously to prove a point.

I've had this happen on more than one occasion. Drivers become fascinated with my e-bike and slow down to get a closer look but piss off the drivers behind them in doing so. Then when they finally pass me, all the drivers behind them decide to take their frustration out on me.

I had one driver nearly run me off the road, then pointed to the sidewalk when I caught up to him.

EBikeFL
07-13-13, 12:36 PM
Long story short, if your moving fast enough to keep up with traffic, don't wipe out, and hold your position in the cue at the reds and stops rather then filter up because doing so can make some drivers go nuclear on you when they end up passing you multiple times and more then minus out any safety gains you may have made by keeping up with traffic better with more speed. Now if you can make good enough time to outrun them altogether, then it is worth considering filtering up but use some discretion on that as well.

You make a good point turbo1889. I don't filter when I stop at stoplights. I do take the center lane and hold it until I get across the intersection. I had a motorcycle filter up and pass me and several cars to make a right hand turn once. I couldn't believe what I was seeing, there was very little room for him to navigate but he did it anyway.

wphamilton
07-13-13, 12:36 PM
My point is the faster you go, the more carefully you need to ride because the harder you go down if you go down....

It may sound picky, but not necessarily. mass x g x height is the same at any speed. That's not just snarky because I'd rather fall with a moderate forward speed than a dead stop - easier for either a shoulder roll or forward roll. Hitting an obstruction or another vehicle you (and the other comments) would be right.

Which is all to say that travelling 30 as opposed to 15 isn't all that much more dangerous with respects to falls. Control, cornering and collisions is another story.

turbo1889
07-13-13, 02:51 PM
It may sound picky, but not necessarily. mass x g x height is the same at any speed. That's not just snarky because I'd rather fall with a moderate forward speed than a dead stop - easier for either a shoulder roll or forward roll. Hitting an obstruction or another vehicle you (and the other comments) would be right.

Which is all to say that travelling 30 as opposed to 15 isn't all that much more dangerous with respects to falls. Control, cornering and collisions is another story.

The worst (single vehicle) bicycle wipe out I've had so far was when I lost it going down-hill on a pedal only mountain bike at about 40-mph on a gravel back-road (I was a lot younger and stupider back then) and I absolutely guarantee you that it was far worse at speed and I would have much preferred to be going a lot slower when I took that spill (hindsight being a lot clearer and wiser).

wphamilton
07-13-13, 04:03 PM
You didn't hit the ground any harder for the speed. You'll get more road rash at the higher speed if you're sliding, and probably more impacts if you're bouncing. I've hit the ground at 60 without a scratch or bruise, and at 10 with some pretty serious contusions. Snapped my collarbone on impact with a curb at 25 mph (last year :( ). That's where the higher speed hurts you - anything vertical in your path - and sliding against a rough surface of course. But the energy equation (or momentum also) is not a good representation of how hard you're hitting.

DrkAngel
07-14-13, 12:25 AM
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.

turbo1889
07-14-13, 12:44 AM
There is one additional "safer" factor you didn't calculate. Under the riding conditions you specify if someone does hit you the speed differential comes into play.

Namely if some knuckle head high speed heavy vehicle operator either runs right into the rear of you on your bike or passes so closely there is a sliding physical contact between the right side of their car and your left side and the protrusions such as the mirror, door handle, and trim make multiple impacts with your bike and body along with road rash like burns from the sliding contact with the main smooth body of the car. That kind of "accident" (in quotes for a reason, criminal negligence on the part of the passing vehicle would be more like it) is known as "getting sliced" up here where I live and is a common danger to avoid on the kind of roads you are talking about.

Anyway, long story short if we assume the car is going 60-mph.

----- If a car either rear-ends you or "slices" you on a too close pass and you are going 10-mph the speed of the impact is 50-mph
----- If a car either rear-ends you or "slices" you on a too close pass and you are going 20-mph the speed of the impact is 40-mph
----- If a car either rear-ends you or "slices" you on a too close pass and you are going 30-mph the speed of the impact is 30-mph

Providence-Forbid, if one of the drivers of those faster moving heavy vehicles on the road either plows into you from behind or "slices" you on a too close pass the faster you are going the lower the speed of that impact will be when they hit you and thus the better your chances of avoiding death and/or reducing injuries from the initial impact.

So, provided you are riding on the correct side of the road and not being a salmon (speed gets added rather then subtracted in that case, which is part of the reason you shouldn't ride like that) then you have an additional safety cushion if you are moving at higher speed if someone actually does hit you.

If you ride correctly with traffic the faster you ride and close the gap between the speed of other traffic on the road the better off you are if they hit you. The reverse is true as far as you hitting them (be careful when drafting cars, sometimes they can brake before you can and if you don't leave enough room you can rear-end them, the only at-fault collision I have been in on a bike was when I rear-ended a vehicle in front of me and split a foam bike helmet in half when my head hit the rear of their vehicle, and I was riding a pedal only bike !!!).

009jim
07-14-13, 02:24 AM
You're assuming there is only one type of accident scenario between cars and bikes. Wrong, there's at least 57 scenarios and for the other 56 you are safer if you go slower.

DrkAngel
07-14-13, 04:29 AM
You're assuming there is only one type of accident scenario between cars and bikes. Wrong, there's at least 57 scenarios and for the other 56 you are safer if you go slower.

Exaggerated ... but ... Good point!
Let's compare other traffic situations:

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.

turbo1889
07-14-13, 06:12 AM
You're assuming there is only one type of accident scenario between cars and bikes. Wrong, there's at least 57 scenarios and for the other 56 you are safer if you go slower.

I mainly was focusing on danger approaching from the rear where it is the least likely to be noticed in time by the cyclist to take action to avoid the situation. Even with a good mirror or two you spend less time looking in the mirror and for danger you don't have much say in - that is most likely to come from the rear in the form of getting rear-ended or a too close pass.

I focused on the highest potential of "surprises" for the cyclist and ASSumed the cyclist of sufficient skill and capabilities to make a difference in avoiding the others. I capitalized the first three letters of that word because you may be correct that you can't count on that and its a ill-advised assumption to make. The rider will be the one that makes the choice as to whether those first three letters should be capitalized or not on that one. I try to keep myself on the lower case level but I will admit there have been times where I've managed to turn myself into the capitalized version.

DrkAngel
07-14-13, 07:24 AM
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"!!!

Monsoon
07-14-13, 09:46 AM
And the s**t eating grin they see on your face as you ride the same speed they are, increases the odds of them hating their lives, selling their cars and buying an e-bike.

win-win, bro.

:thumb:

OYO
07-14-13, 11:14 AM
As far as i am concerned nothing ive read here "demonstrates" a faster speed is safer. I run an ebike but i also run 2 trucks & several motorcycles & the single most important factor when assessing levels of safety on urban streets is how other road users assess what risk you are to them if they do something wrong..
for example pulling out of a side turning into your path. unfortunately if you are on a bicycle they tend to assume you are doing alot less that 30mph & after a quick glance at you they will look away & pull out. obviously flowing traffic at a similar speed is safer but not if you are on a small frontal area vehicle which people assume will be approaching at bicycle speeds.
I find the largest frontal area vehicle i drive (a truck) makes people decide not to risk entering my path far more often, even if I'm going extremely slow, however, they happily enter my path if I'm riding my ebike & its down to me to take avoiding action which is most certainly more dangerous at higher speeds..o

Monsoon
07-14-13, 11:45 AM
As far as i am concerned nothing ive read here "demonstrates" a faster speed is safer. I run an ebike but i also run 2 trucks & several motorcycles & the single most important factor when assessing levels of safety on urban streets is how other road users assess what risk you are to them if they do something wrong..
for example pulling out of a side turning into your path. unfortunately if you are on a bicycle they tend to assume you are doing alot less that 30mph & after a quick glance at you they will look away & pull out. obviously flowing traffic at a similar speed is safer but not if you are on a small frontal area vehicle which people assume will be approaching at bicycle speeds.
I find the largest frontal area vehicle i drive (a truck) makes people decide not to risk entering my path far more often, even if I'm going extremely slow, however, they happily enter my path if I'm riding my ebike & its down to me to take avoiding action which is most certainly more dangerous at higher speeds..o

Many of these issues can be resolved by using the appropriate warning device.

http://i.imgur.com/9p9FvrQ.jpg

Shimagnolo
07-14-13, 12:37 PM
Many of these issues can be resolved by using the appropriate warning device.

http://i.imgur.com/9p9FvrQ.jpg

In action: http://vimeo.com/44650294

turbo1889
07-14-13, 05:28 PM
Since we have gotten into the humor end of the discussion, I'll join into that as well:

http://www.twilighthistories.com/wp-content/uploads/2012/08/strange-tank-Armoured-Quadricycle-1899.jpg

http://wtfbot.net/pix/1851.png

http://www.guns.com/wp-content/uploads/2012/12/unicorn-gun-on-bike1.jpg

If OYO is correct that in order for other drivers to respect you on the road you must represent sufficient threat to them ~ I believe that should do the trick. I was looking for a picture of a tadpole tandem I saw years ago on the net with hard mounted double forward gatling guns and the stoker sitting backwards with a single gatling gun on pivot mount for a tail gun but was unable to find that picture and those were the best I was able to come up with on short notice.

OYO
07-14-13, 07:46 PM
hahaha reminds me of this ... at first glance it has a good threat score.
http://i556.photobucket.com/albums/ss3/Bungitonhere/IMAG1089-1.jpg

DrkAngel
07-15-13, 03:22 AM
Better than a horn! Gets you respect ... on sooo many levels!
http://www.bikeforums.net/attachment.php?attachmentid=329219&d=1373879976
329219

DrkAngel
07-15-13, 11:54 AM
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 ...

OYO
07-15-13, 05:20 PM
You are probably safer the faster you ride this ...
https://www.youtube.com/watch?v=z6W7SLpdNaU&feature=youtube_gdata_player

DrkAngel
07-16-13, 07:17 AM
I just re-found a representation of collision rate vs speed differential.

http://endless-sphere.com/forums/download/file.php?id=82193
Collision rate would appear to be 20-25% for the 20m/imgh cyclist vs the 10mph cyclist, in a 30mph traffic environment.

turbo1889
07-16-13, 01:49 PM
Is that bicycle specific or is it just a general rule from car-car collision data?

What are they defining "average speed" as being (do they mean average speed of cars on the road or the average speed of pedal bicycle)?

What was their source data for the curve?

wphamilton
07-16-13, 02:57 PM
I googled "Solomon Curve" and it's evidently research from the 60's graphing the number of car-car collisions against the car's speed difference from the average car speed on the road. I think it confirms OP's intuition about the diminishing likelihood of collisions as you get closer to the motor vehicle speeds.

Monsoon
07-21-13, 09:16 PM
Since we have gotten into the humor end of the discussion, I'll join into that as well:

http://www.twilighthistories.com/wp-content/uploads/2012/08/strange-tank-Armoured-Quadricycle-1899.jpg

http://wtfbot.net/pix/1851.png

http://www.guns.com/wp-content/uploads/2012/12/unicorn-gun-on-bike1.jpg

If OYO is correct that in order for other drivers to respect you on the road you must represent sufficient threat to them ~ I believe that should do the trick. I was looking for a picture of a tadpole tandem I saw years ago on the net with hard mounted double forward gatling guns and the stoker sitting backwards with a single gatling gun on pivot mount for a tail gun but was unable to find that picture and those were the best I was able to come up with on short notice.
well if you really really need to be safe...

http://i.imgur.com/7vZJK1x.jpg

skye
07-22-13, 04:33 AM
OP is making a common but utterly erroneous assumption. Most crashes do not occur as the result of unsafe overtakes; most collisions occur because of motorist inattentiveness (or cyclist error) at intersections, where the protective reduced speed differential favored by the OP can actually become an increased speed differential with deleterious consequences.

In any event, physics is the wrong discipline with which to solve automobile-bicycle safety problems, which are essentially social and psychological in nature.

DrkAngel
07-22-13, 03:40 PM
In any event, physics is the wrong discipline with which to solve automobile-bicycle safety problems, which are essentially social and psychological in nature.

Well ... personally ... my mind is constantly evaluating velocities and vectors of all moving objects in sight.
As well as combining this with variance potential and probabilities.

Physics Rules! ... Quite literally ... Everything!

Sorry, while I might socialize, to some extent, with cars, I just can't psychoanalyze all the vehicles coming at me.

Also ... don't see how that could possibly help?

DoubleDiamonDog
07-22-13, 05:58 PM
Thanks for starting this interesting thread DrkAngel. It seems that many agree with your conclusion that riding faster is safer. I agree with the point that fewer cars will overtake a faster rider but disagree with that it is safer.

While getting hit from behind by a passing motorist is a fear for any cyclist it is extremely rare - so rare in fact that some have argued that a separated lane for cyclists is unnecessary (I disagree and have recently experienced the wonderful separated lanes through downtown Vancouver BC, complete with separate turn arrows for right turning cars - wish we had those everywhere). Here is a bit of interesting info on bike accidents:

http://streetswiki.wikispaces.com/Bicycle+Crashes

My concern with going 30 mph is that cyclists riding to the right in a traffic lane have very limited room to safely maneuver. Imperfections in the pavement - potholes, bumps - or debris in the cyclist's path are more hazardous when going faster. When traveling at a higher rate a cyclist has much less time to see and react to these issues or other hazards such as the clueless driver who pops his door open as you approach.

A sample of one is irrelevant but what the heck - I'll share my experience. I have only had one car/bike accident. I have never been hit by a car that passed me in my lane, but I once had a car approaching from the opposite direction turn in front of me. Apparently the driver didn't see me (in spite of flashing headlight in the day) and attempted to turn into a driveway on my side of the street. I could not avoid the crash and hit the brakes hard and hit the front quarter panel of the car. I was very lucky as after flying over the car my main injury was a fractured wrist (titanium plate, pins and screws still in place ten years later). Yes - there was the slow motion part which allowed me to think "Protect your head, protect your head" as I attempted to break my fall with my hands.

There was some discussion in this thread about how going faster somehow makes getting hit from behind less of an issue - I am not so sure about that - but I think that we can all agree that it makes matters much worse when the car approaches from the other direction and from what stats I have seen accidents with traffic parallel to the rider occur with about the same frequency with cars coming from the opposite direction as with going with the direction of the cyclist.

turbo1889
07-22-13, 10:35 PM
@ DoubleDiamonDog

As to separate cycle lanes not being needed and/or cyclist riding to the right of the main flow of traffic. I would be one of the ones that argues that it depends on the speed of the main flow of traffic (assumably the heavy vehicle traffic, it will be the "main flow" for quite a while longer I'm afraid). On roads with a speed limit of 25-mph or less and/or the main traffic flow is moving at that speed I find separate cycle lanes and/or riding to the right of the main flow of traffic to be not only unnecessary but more dangerous for the cyclist then riding in the main flow of traffic "taking the lane". On the other hand on roads where the speed limit is 45-mph or more and/or the main traffic flow is moving that fast if there is a safe, sane, and effective place to ride that is to the right of the main traffic flow and out of their way I most certainly find it best to ride there and I would most definitely like it if there were an official cycle lane available (provided it was done in a half way sensible way, as in someone who actually bikes as transportation laid it out and decided how it was routed through the intersections).

And I can most certainly assure you that at least when you are riding "All In" (my term for riding with the main flow of traffic in low speed areas just like I were a motorcycle) instead of riding "Out" (my term for riding to the right of the white line on the shoulder edge out of the main traffic flow and out of the main lane) maintaining sufficient speed to make a good effort to keep up with traffic not only keeps you safer as far as rear impact capability and not getting passed as often and not making people behind you impatient. But far more importantly it earns you a huge amount of respect with other road users - or at least that has been my experience. Yah, there are still some obnoxious selfish idiots you have to deal with, and a few that have a deep rooted hatred towards cyclist, and there are a few on the other end of the spectrum who actually understand the rules of the road and will treat you right regardless, but for a huge segment of other drivers around you keeping up with traffic and maintaining speeds that at least approach theirs makes the difference in whether they treat you as an equal road user or not. In stop and go in-town, square grid, traffic I can do that under pedal power breaking above 20-mph under pedal power alone and accelerating up to speed as quick or quicker then they do. I can't do that for an extended period but with the little rests I get when waiting for the lights to turn I can do it and it makes a huge difference.

When riding "Out" on the right edge of a high speed roadway, then what DrkAngel has to say about not getting passed by as many vehicles while covering the same distance and those vehicles having more time to notice you before passing you does come into play. But as you say for the "Left-T Crossers" especially (the guys who turn left across your path when they don't have the room to do so safely) running at higher speed could be a hazard giving you less time to brake and avoid the collision and making for a harder hit if there is a collision.

Allen
07-23-13, 01:33 PM
Moved from Electric bikes

Chris516
07-23-13, 02:37 PM
Faster is Safer!
My Sister-in-Law just can't understand, why I feel that going faster, on a bicycle, is safer. "30 mph!" ... "You're gonna kill your self!". ...

I feel it necessary to prove that, up to the speed of surrounding traffic, faster is safer. Let me try a mathematical approach.

First, let me qualify;
1. My riding is in an urban area and 95% of the streets-roads are 30 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.

30 mph traffic:

At 10 mph -
60min x 10cars - 1/3 (for 1/3 speed of cars) = 400 cars passing you at 20mph.

At 15 mph -
40min x 10cars - 1/2 (for 1/2 speed of cars) = 200 cars passing you at 15mph.

At 20 mph -
30min x 10cars - 2/3 (for 2/3 speed of cars) = 100 cars passing you at 10mph.
AND, cars have twice the time to notice, and avoid, you! (vs 10 mph).

At 25 mph -
24min x 10 cars -5/6 (for 5/6 speed of cars) = 40 cars passing you at 5mph.

At 30 mph -
20min x 10cars - 3/3 (for 3/3 speed of cars) = 0 cars passing you!

(Math is simplified - but "sound")

When you consider that many bike accidents are directly related to passing cars, especially in a "road" environment, then 20 mph would be (4 times safer than 10 mph) x (2 - twice the time the, approaching, driver has to see biker) = 8 times safer @ 20 mph, compared to 10 mph!

Most impressive is that each speed increase of 5 mph reduces the volume of passing traffic by 50%!

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 4, only 1 @ 20 mph and at 30 mph you might never encounter 1.
Don't forget 'lane position' in that methodology. On a regardless of the speed you may be traveling, if you are 'hugging the curb', you are not making yourself known, and traffic will still blow by you, like you are just a 'speed bump'.

Keith99
07-23-13, 03:44 PM
Don't forget 'lane position' in that methodology. On a regardless of the speed you may be traveling, if you are 'hugging the curb', you are not making yourself known, and traffic will still blow by you, like you are just a 'speed bump'.

Good point.

Honestly my single biggest problem (still not huge) was potential right hooks. Generally NOT jerks, just people thinking they had time to pass before a turn and finding out too late they did not.

Going at a speed that others do not expect often results in them initially assuming you are going at the speed they do expect.

I also do not like riding an intersection at my max speed. I want to be able to either slow or accelerate significantly. Same as when driving.

DoubleDiamonDog
07-23-13, 04:26 PM
@ turbo1889

The beauty of the system in Vancouver is how it improved matters for drivers and cyclists. In the crowded, high traffic West End, they have selected some key streets and eliminated curbside parking, placing planters between the vehicle lane and the cycle lane in the old parking strip adjacent the curb. At the corner, a right turn arrow allows the vehicles next to the bike lane to make a right, then a turn is not permitted and the cyclists and other traffic lanes go, so it prevents the conflict of the right turn. Left turn functions similarly after the straight and bikes lanes turn red. The result is that cyclists seek out these safe routes and use them to efficiently flow through the city, keeping them off of the other streets where cars do not encounter them. I thought that it worked extremely well. In other areas they have the typical situation you describe - a painted lane for cyclists adjacent to the traffic lane. These are parts of a system with a separate recreational path shared by bikes and pedestrian along the waterfront, all around the peninsula and various traffic calming devices and vehicular dead-ends that reduce traffic on some streets to make them more bike and pedestrian friendly.

Chris516
07-23-13, 05:06 PM
Good point.

Honestly my single biggest problem (still not huge) was potential right hooks. Generally NOT jerks, just people thinking they had time to pass before a turn and finding out too late they did not.

Going at a speed that others do not expect often results in them initially assuming you are going at the speed they do expect.

I also do not like riding an intersection at my max speed. I want to be able to either slow or accelerate significantly. Same as when driving.

Right-hooks, are one reason I 'take the lane'. So, I can see them coming and have enough time to react.

As for going at a speed they don't expect, I feel that is a two-fold problem. Even if a cyclist is going say 25-30mph on a 30mph road(or even a 40mph road), some motorists' don't like it regardless of the fact that, they are not being slowed up in traffic, anymore than a motorized vehicle might do the same thing.

Staying with the point of how many vehicles pass depending on the cyclist's speed.

Behaviorally, A motorized vehicle will not pass another motorized vehicle, with the same amount of hostility. That they have, when they pass a cyclist. Because they consider them 'equal', instead of 'less than'.

So the greater the speed and lane position of the cyclist, the greater chance of equality.

JoeyBike
07-23-13, 08:03 PM
Faster is Safer!

I could not agree more.

Here is an old post (2007) from a Blog of mine (http://joey-bike.blogspot.com/p/how-i-ride-safe-in-nola.html). Enjoy!

"When I hit the road at the end of the bike path I tried to become part of the traffic flow immediately. I enter St. Charles Avenue a few blocks west of Broadway and Audubon Park. I did whatever it took to limit the number of vehicles overtaking me from the rear. For the next four miles, all the way to Lee Circle, I could usually maintain speeds between 20 and 24 miles per hour even though the road surface is not perfect. If I could draft a line of traffic and catch a few green lights it was possible for me to hang at 25 mph for a couple of miles. Early in the morning when school was out, it was normal for me to make the entire run and be passed by five or less vehicles. Zero passing vehicles was a rare treat that really got my crest waving high in the air."

DrkAngel
07-24-13, 09:55 AM
I also do not like riding an intersection at my max speed. I want to be able to either slow or accelerate significantly. Same as when driving.

Personally ... I can decelerate from 20mph to dead stop in about 1 car length ... (less than 2 seconds~).
Might take me 10 seconds and the length of several intersections to go from 10mph to 25mph.

So I would much rather maintain good speed and slow quickly ... than cycle slowly and rely on comparatively feeble and desperate acceleration!

Booger1
07-24-13, 01:05 PM
If the cars are only doing 30MPH,you must be talking about getting hit in a parking lot...:)

If you do get hit at any speed,chances are,the only math you need to know is how to add.....so you know how much the doctor bills are.

degnaw
07-24-13, 01:27 PM
I'll preface by saying that I always go as fast as I comfortably can, because I don't think the safety differences are significant. That said, I do believe slower (within reason - let's say 15mph) is safer than faster (20+):

-Motorcycling is more dangerous than cycling
-Drivers aren't expecting cyclists to go fast - thus, they're more likely to right hook, left hook, or pull out in front of faster cyclists because they wrongly assume they can make their maneuver in time.
-Faster moving cyclists are harder to see, leading to more left hooks and pull-outs.
-IF you get hit, with the exception of a rear-end collision, you're a lot better off at a lower speed.

Keith99
07-24-13, 01:36 PM
Personally ... I can decelerate from 20mph to dead stop in about 1 car length ... (less than 2 seconds~).
Might take me 10 seconds and the length of several intersections to go from 10mph to 25mph.

So I would much rather maintain good speed and slow quickly ... than cycle slowly and rely on comparatively feeble and desperate acceleration!

Most TDF cyclists envy your ability to stop.

spare_wheel
07-24-13, 01:54 PM
Most TDF cyclists envy your ability to stop.

Mebbe those TdF riders should learn how to skid and/or buy some disc brakes. Just sayin'

http://www.exploratorium.edu/cycling/brakes2.html

spare_wheel
07-24-13, 02:03 PM
@ turbo1889
The beauty of the system in Vancouver is how it improved matters for drivers...keeping them off of the other streets where cars do not encounter them.

I call this ugly.

I-Like-To-Bike
07-24-13, 11:39 PM
I also do not like riding an intersection at my max speed. I want to be able to either slow or accelerate significantly. Same as when driving.

Personally ... I can decelerate from 20mph to dead stop in about 1 car length ... (less than 2 seconds~).
Might take me 10 seconds and the length of several intersections to go from 10mph to 25mph.

So I would much rather maintain good speed and slow quickly ... than cycle slowly and rely on comparatively feeble and desperate acceleration!
See http://www.slate.com/blogs/the_slatest/2013/07/24/sf_cyclist_felony_manslaughter_chris_bucchere_believed_to_be_first_ever.html

Relevant info from the speedy cyclist:
"Around 8 a.m. I was descending Divisadero Street southbound and about to cross Market Street. The light turned yellow as I was approaching the intersection, but I was already way too committed to stop. The light turned red as I was cruising through the middle of the intersection and then, almost instantly, the southern crosswalk on Market and Castro filled up with people coming from both directions. The intersection very long and the width of Castro Street at that point is very short, so, in a nutshell, blammo. ... It was commuter hour and it was crowded as all getup. I couldn't see a line through the crowd and I couldn't stop, so I laid it down and just plowed through the crowded crosswalk in the least-populated place I could find."

DrkAngel
07-25-13, 12:08 AM
Mebbe those TdF riders should learn how to skid and/or buy some disc brakes. Just sayin'

Actually ... skidding will increase stopping distance.
The most effective braking requires well trued wheels, (for rim brakes), adjusted brakes and a "feel" for the precise point before wheel lockup.
Yes, it does require practice!

I've tested to the point of a lifted rear wheel ...