Bicycle Safety - The Math of Speed.

Discussion in 'Road Bikes' started by DrkAngel, Feb 14, 2010.

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  1. DrkAngel

    DrkAngel New Member

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    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!". ... [​IMG]

    I feel it necessary to prove that 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.

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

    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!

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

    (Math is simplified - but "sound")

    If you concede that most urban bike accidents are directly related to passing cars, then 20 mph would be (4 times safer than 10 mph) x (twice the time the, approaching, driver has to see biker) = 8 times safer @ 20 mph, compared to 10 mph!

    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.
    [​IMG]

    [​IMG] EZip Engineering 101 [​IMG]
     

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    Last edited: Feb 14, 2010
  2. Barmy

    Barmy New Member

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    What about

    The AHs that are coming at you. Using math you have:

    An impact of net 40 mph when riding at 10 mph (Your 10 plus the AHs 30 mph)
    An impact of net 50 mph at 20
    and an impact of net 60 mph at 30 :D
     

  3. hophead

    hophead New Member Tavern Member

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    You are correct in theory. The The Solomon curve backs up your assertion.
    [​IMG]

    In reality, in the absence of cops or speed cameras, no one drives the speed limit. In a 30 mph zone,expect motorists to be driving 40 mph or more.
     
  4. Nigal

    Nigal YAY BAIKS! Tavern Member

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    Let's face it, if you can maintain 30mph average speed you are not only a better man than I but you are immortal and can't be killed. :p
     
  5. Grape Ape

    Grape Ape Younger than Hack Tavern Member

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    No no no you have it backwards. They are traveling the same direction. So the net vehicle/bike impact speed is equal to the speed of the car - the speed of the bike. So bike going 10 mph and car going 30 impact speed is 20 mph. Bike going 20, car going 30 impact speed is 10. The issue here is that you on the bike should have swerved and went around the car.

    Now the bad part is that if the car speed is above the bike speed then the vehicle/bike impact speed starts going up. If the bike is going 30 and car is going 50 then you are back into the 20mph impact speed but now you have the issue of 20 mph vehicle/bike net impact speed and the sudden bike acceleration issue then the bike road impact speed which will be close to initial vehicle impact speed . So if you are on a bike going 30 and get hit by a vehicle going 50 the vehicle impact is 20 mph and the ground impact is 50. So it will hurt just a little bit.

    Now it may sound like a good deal but in truth the following is the worst possible scenario. Bike is going 30 mph car is going in the same direction at 30 mph. They hit each other. It sounds like it is a good deal but it is not. Such an accident will rip the space time continuum. The bike and vehicle will meld into a weird conglomeration of carbon fiber and hydroformed steel. Behind them a large black hole will form and start the implosion of the entire universe. Now if the conglomeration vehicle maintains a constant speed that is equal to the speed of the accident then the universe's implosion will occur at a time equal to actual time of the current universe's doom. If they slow down then the time for destruction will be in proportion to the loss of speed. Slower they go the faster the universe implodes. The only hope is for an increase in speed. Such an increase will lead time to reverse. The reversal will back time up to the point of the meld and the 1 will again be 2 and the wreck can be avoided to save the universe. So remember if it ever happens to you Stand up and crank up the speed.

    At least I think how all that stuff works.
     
  6. DrkAngel

    DrkAngel New Member

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    I'm an out of shape 51 year old, with a poor heart. I got a cheap Ezip Mountain Trailz 2 years ago, electric assist bike, and have been tweaking it into an awesome road machine.

    Stock: .................................... Modified

    24v Sealed Lead Acid Batteries ... 37v Li-ion batteries (50% speed increase)
    450w motor @ 24v ................... 675w motor @ 37v
    20T motor side freewheel .......... 16T motor side freewheel (25% speed increase)
    7spd 14-28T gear freewheel ...... 7spd 11-32T gear freewheel (32% pedal speed increase)
    16-17mph top speed. ............... 30mph capable w/ pedal assist!

    Motor alone "bogs" near 27mph, pedal assist appreciated!
    Some assist through 32mph.

    Check my postings under : http://www.twospoke.com/forum/f41/


    [​IMG] EZip Engineering 101 [​IMG]
     
    Last edited: Feb 16, 2010
  7. DrkAngel

    DrkAngel New Member

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    Accident :<(...
     
    Last edited: Feb 14, 2010
  8. DrkAngel

    DrkAngel New Member

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    OOPs!
     

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    Last edited: Feb 14, 2010
  9. DrkAngel

    DrkAngel New Member

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    Unless you are riding on the wrong side of the road, I can't imagine how this could happen. The odds on a driver being a big enough AH to cross the oncoming lane and "hunt you down" might be 1 in 100 million, if you're "Black" maybe, 1 in 10 million, if you just dumped a "Lover" maybe, 1 in a thousand.

    Oh! If you are riding against traffic, then you might have a valid concern. This is illegal and very unsafe! The greater your speed, the more damaging the impact and the less time the driver has to notice you.

    Pedestrians are required to walk against traffic but bicyclists are required to ride in the same direction as traffic. good rear view mirror is highly recommended!

    [​IMG] EZip Engineering 101 [​IMG]
     
  10. Barmy

    Barmy New Member

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    What about

    the driver who is sleepy and nods off... or one who has to much to drink... or in my case misjudges your speed and cuts a left hand turn in front of you....I woke up in the hospital and spent a couple of days in the "head injury ward"
    :eek:
     
  11. Farnsworth

    Farnsworth New Member

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    With out any attention to the numbers I feel safer going slow. Fast makes me worry. Especially in the city.
     
  12. DrkAngel

    DrkAngel New Member

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    Bicycle Safety - Basics

    There is always disrespect & outright danger for bicyclists.

    There are many things that can be done to make riding safer and more enjoyable.

    1. Obey the law!

    Please remember that we have most of the rights, and responsibilities!, of motor vehicles.

    Ride with traffic. Bicycles are, legally, to ride on the right side of the road, with traffic, not against traffic.

    Signal for turns and always STOP at stop signs & red lights.

    Although you have the right to a traffic lane you will get all the respect of an old fart putting along at half the speed of traffic. When possible use less traveled “side streets” and always stay well to the right, so as to NOT hold up traffic.

    In regards to pedestrians, they have unequivocal priority over the Biker. You stop for them & give them every possible right of way.
    If you ride on a sidewalk, especially "in town", be aware of doorways, keep your speed moderate enough so that you can stop, or swerve, for any exiting shoppers.

    Remember, respect is earned. The definition of a good driver is that they "blend smoothly with traffic". This applies equally to the biker. Obey the laws and respect others rights. Makes everyone’s day much better.

    2. Be seen!

    Most all bike vs car accidents are because "I just didn't see him."
    I equipped my bike with;
    1. Tail-turn signal-brake light
    DealExtreme: $8.65 9-LED Turning Signal Lights with Electronic Horn for Bicycles (2*AA)
    2. Wide angle LED headlight with low, high and strobe function
    a. Reversing light, in "mount", provides much better "balance.
    b. 3-aaa can be replaced with 18500 Li-ion (rechargeable).
    DealExtreme: $11.99 Flood-to-Throw Zooming Cree P4-WC 3-Mode LED Bike Light with Mount (3*AAA)
    3. I also wear a red flashy light on the back of my hat-helmet
    4. Found some air horns at local "Dollar Tree" store, taped one to steering column, nice "panic button!" .... Pictures below!

    3. Be Aware!

    Most important is to be aware of what's going on. No one is going to look out for you better than yourself!
    Personally, I could not find a rear view mirror that I was happy with, so I designed my own. I attached a small "inspection mirror" to a hair clip, with some duct tape.

    .... Pictures below!

    4. Keep your bike in good condition.


    Check your tires for possible damage & proper inflation, also check spokes.
    Check all components for excessive wear, tightness, squeaks etc.
    Most important is check and adjust brakes, frequently!

    [​IMG] EZip Engineering 101 [​IMG]
     

    Attached Files:

    Last edited: Feb 24, 2010
  13. photosbymark

    photosbymark New Member

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    Your Math

    Well the extra speed would give a slower closing rate, but you forget one thing. Closure rate doesn't matter once you do hit something. It has been for ever since I dealt with any of these formulas, but IIRC the force of an impact is the mass times the acceleration. Throw in a few variables like the duration of the impact to boot and one thing is clear.

    The faster you go, the greater the impact regardless of closure rate. Big fat guys like me are going to hit harder than little guys. We have more mass. If you stay on the bike or more likely get hit by it, the heavier the bike the greater the impact. Spread the time of the impact out by hitting something like hay bales, and the acceleration is reduced and you don't hit nearly as hard.

    You may not be as likely to get hit going 30 and up to the speed of the surrounding traffic, but if you do get hit its gonna hurt worse. Do the calculations. I am just not inclined to drag out math skills I haven't used in 30 years to get exact numbers.
     
  14. DrkAngel

    DrkAngel New Member

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    Being hit ... or hitting something.

    All examples are based on 30 mph traffic speed and a comparison of 10 mph and 20 mph bicycle speeds.

    Of course, faster speed will produce a more damaging impact! BUT!!!

    I am speaking of the danger from other vehicles. In a worse case of a direct rear collision, a 10mph, (bike speed 20 mph), impact might only slightly damage the bike and leave the rider seated and sensible, capable of recovering, or a controlled "crash", while a 20 mph, (bike speed 10 mph), impact would probably unseat, injure and render, the rider, dazed or senseless, fully at the mercy of the road, and traffic. At any speed, if hit from behind by a vehicle, you will almost instantly be accelerated to 30mph. At 20 mph the initial impact will be 1/2 the severity of the bike at 10 mph. Of course secondary impact might be the same, except, rider would be in much better physical, mental and mechanical condition to escape, or lessen, injury.

    On a lighter note, a swipe from a mirror, door handle, or even, fender at 10 mph, (bike speed 20 mph), might bruise but would probably leave the biker physically and mechanically in good condition, while a 20 mph, (bike speed 10 mph), swipe would very likely cause major physical and mechanical damage and very likely a nasty crash. Most any biker would prefer a 20 mph controllable "redirection" to a 10 mph uncontrollable "crash".


    [​IMG] EZip Engineering 101 [​IMG]
     
    Last edited: Feb 24, 2010
  15. photosbymark

    photosbymark New Member

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    Yes you might get by with a bump at 10mph, but you are not doing 10. You are doing 30 and the contact patch of that tire knows that as well as the co efficient of friction. Swipe a mirror or a door at that speed and Id take odds you are going down. Any side load at all and it will happen so fast that if you stay on the bike you are more lucky than good. Even that swipe from a mirror is going to deflect your handlebars quick enough that you will be down before you can say Uh Oh.

    The only way you have a chance to stay on the bike is a hit square in the rear wheel on something other than the tire. Anywhere else and your are down. What the other car was doing then isn't going to matter. If it hits your rear wheel you are going to upset the apple cart by that outside force acting on the spinning of the rear wheel effecting its gyroscopic effect that is keeping you upright. Unless the bike you are riding has a rear bumper, a hit from behind will put you down as quick as anywhere else. You ain't bump drafting on the back straight at Daytona. All but the dumbest of cup drivers have figured out not to bump draft in the corners and if you don't hit em sqaure you can wreck em on the straight.

    You might blend with the flow of traffic better at the extra speed. The other drivers might like you better and may actually pay a bit more attention. You also may get less space than you would going slower because they are not closing as fast. That doesn't draw as much attention to a driver talking on the cell phone. Either way it doesn't matter. In all but the most unusual situations the odds are you are going to be on the concrete. If you want to test it, its going to hurt. How bad will depend on how far you slide before you hit something solid, what it is and how much speed you scrub off with skin.
     
  16. DrkAngel

    DrkAngel New Member

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    Speed Kills ... NOT!

    All calculations are based on:
    1. a 30 mph speed limit
    2. 10 mile trip
    3. traffic density of 10 vehicles per minute passing a static point
    4. bike speed of 10 mph vs 20 mph vs 30 mph

    There will always be the odd driver "Not Paying Attention" (NPA). 1 in 50?

    On a 10 mile trip:

    1. at 10 mph, you will be passed by 400 vehicles, flying by at 20 mph.
    . NPA driver has 8 seconds to notice biker, = 8 NPAs
    .. NPA danger 800% greater than at 20 mph!!!

    2. at 20 mph, you will be passed by 100 vehicles, coasting by at 10 mph.
    . NPA driver has 16 seconds to notice biker, 2 NPAs/2 (double time) = 1 NPAs
    .. NPA danger reduced by 87.5%!!!

    3. at 30 mph, you will be passed by 0 vehicles, maybe 1 or 2 speeders.
    . NPA driver, not a factor, or number reduced to the infinitesimal

    [​IMG] EZip Engineering 101 [​IMG]
     
    Last edited: Feb 27, 2010
  17. wild

    wild Yesterday tired old man, Today retired old man

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    Come on now who is going 30 in a 30mph zone. The cop down the street ticketed the school bus driver for 60 in a 25mph. I don't think there is a speed limet on one of the roads I drive on.
     
  18. DrkAngel

    DrkAngel New Member

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    Our local speed limits are strictly enforced!

    However, at higher vehicle speeds, higher bicycle speed is an even more important safety factor. Most noticeable is that the driver has much more time to notice and accommodate the biker.

    [​IMG] EZip Engineering 101 [​IMG]
     
  19. photosbymark

    photosbymark New Member

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    How many times you are passed does not equate to safety. You can have a car pull out in front of you because you are on a bike and not seen just as easily at 30 as you can at 20 or any other speed. The car coming up from behind you and passing you is probably the place where you are MOST likely to be seen. Can you still get hit? Sure. Yet I believe you are far more likely to get hit by a car pulling out from an intersection that did not see you because they were not EXPECTING a bike to be there an were looking for cars. Worse than that is the fact that your braking distance is going to be longer and so you need more time to avoid it. It requires more distance to make a evasive maneuver, and the time to make that maneuver will be greatly reduced. Further more if you have a mechanical failure such as a tire or a brake failure, then you problems are magnified. Yes I was headed down a hill one day when a snake of the poisonous variety slithered on to the road. I grabbed both brakes hard. The back brake worked, but the front failed. The bike went down on one side of the snake and I came down on the other.

    Does speed kill? Not necessarily but if you have an impact that impact will by math be proven to be a larger hit and on a bike with NO protection from that impact, its going to hurt and maybe bad. Now like most things, there is not a risk free option. If you don't like to be passed, then faster will keep that to a minimum but at the price of a greater impact does happen.
     
  20. fleeter

    fleeter The Bearded Wonder

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    DrkAngel's statements are true if we were in a perfect world, while it seems that everyone else is arguing for the "worst case scenario." I think that, yes, DrkAngels assumption of matching the speed is better in terms of reducing or eliminating the vehicles that would normally overtake you...
    ... on the other hand, you do have to take into consideration the human factor, and that even though your speed limits may be "strictly enforced," that isn't a guarantee that nobody is going faster, or isn't paying attention, etc.

    In an ideal world, I believe matching the speed would be better. However, in my neighborhood, I would rather be a little slower and cautious (plus I can't even get up to 30mph!). But again, it seems like we're comparing apples to oranges.
     
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