The city I live in has just installed cycle boxes in front of traffic at light controlled intersections. This has spark a lot of debate online.

My experience is that I will generally, through timing and being ready in the correct gear, be able to clear the intersection from a stand still before any cars will.

Is there any science to back up my observation?

  • I'm a bit confused about what the question really is here. Are you wondering from the point of view of assessing whether cycle boxes are a good thing for cyclists, for traffic flow generally, for safety? Even if the cars have to wait a moment, it could still be a good idea for cyclist safety. – James Bradbury Apr 2 '13 at 8:13
  • No I believe cycle boxes improve safety. What I would like to know if there is any science behind my belief that cycles can be faster on starting and over the first 10m. I know power to weight ratio is stacked heavily in favour of cars. – DWGKNZ Apr 2 '13 at 10:27
  • Somebody else will be along in a while with some equations, but my experience of such boxes (known as advanced stop zones, ASZs, in the UK) is that cyclists are quicker away because we, erm, tend to predict the green light better than the cars, so there's a time lag before the vehicles go as well as whatever minimal acceleration advantage. – Unsliced Apr 2 '13 at 10:44
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    It depends on the cyclist and the conditions. An average cyclist, on a relatively flat surface, can accelerate away from a stop fairly quickly. But if the cyclist taken time to saddle up and take off (maybe has trouble clipping in, maybe isn't so strong and it's slightly uphill) then it can go much slower. (I personally dislike the pressure of cars behind me when I'm starting -- prefer to be off to the side where I can take my time.) – Daniel R Hicks Apr 2 '13 at 11:06
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    Do you expect every cyclist in your city to explode off the line when the light goes green? Even people who are able to out-accelerate a car will, from time to time, miss the light changing or miss clipping into their pedals or forget to preemptively shift to a lower gear. – user229044 Apr 2 '13 at 15:36

It's a size versus distance thing. You are lighter and so your acceleration has a more immediate effect (and I'm sure some physicist will tell me I'm wrong on the cause...but this is how my memory stored in when I took junior high physics MANY years ago). For a short distance you should win if you can come off the line in the right gear and at the right time. You can probably beat most cars that aren't really flooring it for about 30'.

If the distance is shorter, a runner would win. Even shorter and an ant would take the checkered flag (if memory serves, the ant wins at 1cm or shorter).

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  • F = ma. Or rearranged: Acceleration = Force / Mass. It's not immediately clear that a smaller vehicle will accelerate faster, as it may also have less Force. – James Bradbury Apr 2 '13 at 8:14
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    There was a demonstration on one of the kids science programs on TV in the UK a while ago. A sprinter, a high performance car and a cyclist did a 10m race. The sprinter won, the car was second and the cycle third (by quite a long way). The explanation there was power to weight ratios. – DanS Apr 2 '13 at 8:38
  • In a race, I'm sure the car would outdo the bike, but cars don't usually (and shouldn't) race out of the intersection. Also, being in the right gear is very important for how quickly the bike accelerates. I generally accelerate quite slowly out of the intersection on my fixie, as the gear isn't optimized for starting out. Also, even if you're in the correct gear, in a commuting situation, there's a lot of cyclists who just don't want to reach a high speed, and their speed coming out of the intersection is quite slow because they only exert a minimal amount of force. – Kibbee Apr 2 '13 at 13:54
  • Well, a size versus distance versus energy thing. A bullet, from the smallest BB to the largest cannon ball, accelerates faster than a car or cyclist or runner or ant. – user229044 Apr 2 '13 at 15:47

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