Monday, 16 February 2015

Bikes use more road space than cars when moving...

At 10mph a bike uses 20% more road space than a car... even when the car only carries its driver. And as the speed goes up, the bikes road use goes up faster than the cars!


Got into tweet exchange with some loony^H^H^H^H^H misguided cyclists over insurance, licencing etc... Got to the usual 'bikes take less space so cause less congestion bit with the usual image...

However this image has always annoyed me as it shows *parked* vehicles, not moving ones. If you are designing a car park, fine, but for road planning it it nonsensical.

So the figures... (from first reliableish looking google search result in each case).

An urban cyclist rides at 10mph, a bike is approximately 6' long, and needs about 13' to brake from 10mph (thinking distance assumed to be the same car/bike so ignored) - and minimum recommended cycle path width is 5' (1.5m) - so at 10mph a bike (carrying a single person) uses 5' by 19' of road space. About 1.5m by 6m

A small car is about 5' wide and 13' long, at 10mph it needs 4' of breaking distance (thinking distance ignored again as same as for bike, so cancel out). So at 10mph a small car (regardless 1-4 occupants and luggage) uses 5' by 17' of road space. About 1.5m by 5m.

So to travel safely a bike uses over 1.5sqM of road more than a car (whether the car is carrying 1 or 4 people!).

In addition a car can reliably and consistently go at a particular speed - right up to the speed limit (or other safe speed) so meaning no passing is required. Whereas a bikes speed depends on the fitness/strength/recovery of the cyclist - so closing up/passing may be frequently needed - causing confusion, stress and conflict.

And if a cars are travelling faster, then they are (of course) using the space they occupy for less time... So at 10mph a bike and solo driver may be on par, but in most other circumstance, the car uses less road space than a bike - a quarter with 4 passengers, and half for each additional 10mph of speed.

So there you go - bikes need smaller parking areas, but use generally use more road space to get you there later and unfit to do anything once you arrive!

**Edit** to put some linkable data in - the highway code breaking distances starts at 20mph, but going with that... And giving the bike figure the benefit of the doubt that it does include thinking distance.

Highway Code (UK government body): The breaking distance for a car at 20mph is 12m/40'
The CycleScheme (a pro-cycling group): The breaking distance for a bike at 20mhp is 18m/60'

(Notwithstanding the fact cars have anti-lock breaks, are regularly MOT tested and are driven by trained/licensed drivers who are required to be alert/sober etc.Whereas a bike has what ever brakes it happens to have, in whatever condition they happen to be in and may be ridden by absolutely anyone).

**Edit** 12/12/2016
Another tweet war... a few more issues addressed.
1) Bikes can ride abreast.
From rule 60 at
So the maximum is two, and not on busy roads. A car may of course carry up to 4 in the space it occupies.

2) Bike braking distance disputed
An experienced rider, on a well set up bike, doing emergency stops on a 'gentle slope' and his best results so reasonable to assume an average rider won't improve, and will probably do a lot worse(!). But is in the same region as the figure used  (13' = 156") - stopping before hitting, rather than touching.


  1. A bike, of mass about 0.1 tons, travelling at 10mph (4.5 m/s) requires 3 times the stopping distance of a car (mass 1.5 tons) travelling at the same speed? I'll forgive you the calculations, but you're assuming that a car can impact a force to mass ratio of over 4 times higher than that of a bicycle? Where are you getting these numbers? This isn't including coefficients of friction of the surface to the tyres, mechanical condition, or anything like that.

    A well-maintained, cheap, road bike will stop in 3 metres in the dry from 20mph - this pales into insignificance compared to high quality road bikes and again in comparison to mountain bikes.

    Not including reaction time is also skewing the numbers in bias favour of the anti-bicycle argument, as the higher road position and greater visibility puts the cyclist in a better position to react to the conditions and react more quickly.

    I put to you that there is no waste of space on the roads for any road user - and this poorly thought out, immature and irrelevant argument breeds nothing more than anger between road users which, ultimately, leads to deaths and injuries.

    If you wish to be taken seriously - as a blogger or as a parliamentary candidate, lose the rhetoric, and come up with some facts.


    Colin - Driver, competitive cyclist, mechanic, mechanical engineer.

    1. I use published braking distances (sources in the links).

      You suggest that braking distances don't matter for bikes because a bike crashes don't really matter. That is an interesting idea, but not one I think you'll get much support for - cyclists are endlessly on about safety...

      The figures I used for bike braking distances are from the links I gave, however as there is no regulation of bikes brakes - this is very generous, as a defensive road user should be allowing for the worst case and assume that a bike has virtually no braking at all.

      You think the average cyclist should be riding closer to the car in front because reaction time is quicker? I refer you back to my first comment on cycle safety.

      Funny that cyclists are so keen to ignore safety to justify their use of the road, but so fussy about it after the fact.

      You have added nothing that wasn't already accounted for - the blog posts stands.

    2. Here is a link to a photo of at least 28 people moving on bikes in enough space for 4 or 5 cars:-
      No massive gaps for braking but they are all safe (other than the danger from the cars). Your dogma does not match real life.

    3. I have no dogma here - I just present the law and established best practice.

  2. Two articles regarding braking distance of bikes, which are not the same as those cited in the single article. There are more

    Reasons for congestion

    None of which suggest that bicycles contribute to congestion

    Bikes take up as much space as a car

    Lets examine the claims made in the blog post

    "A small car is about 5' wide and 13' long, at 10mph it needs 4' of breaking distance (thinking distance ignored again as same as for bike, so cancel out). So at 10mph a small car (regardless 1-4 occupants and luggage) uses 5' by 17' of road space. About 1.5m by 5m."

    Lets look closely at this, the minmum carrigeway width is 6m. When calculating the width needed for a cycle 1.5m minmum width for cycle path so must use same comparison. So space for a car is 6m by 5m, compared to cycle 1.5m by 6m.

    Why does this cacluation take in account braking distance? That has little bearing on congetsion, as this effected by the volume and hence the size of the vehicle causing congestion.

    The author does not even have the courtesy to engage in any form of debate. Whilst attempting to discuss this topic via twitter, the authors response was to block the account. Despite offering all reasonable courtesy, the only thing l can conclude is this author is not interested in open debate. Thier only interest is in discussing topics with those whom agree with them.

    Will this comment be deleted, oh yes it will be just like my twitter account was blocked.

    1. Your citing of cycle paths is actually confirmation that bikes on existing carriageways is an inefficient use of that road space. You make my point for me.

      The huge amount of abuse I got from cyclists on twitter for this simple blog (including the publishing personal details, digging through one of my companies financial accounts etc) is why I freely block on twitter.

      And given the size of your reply, tweeting it at 140 chars a time would be a bit stupid don't you think?

  3. "Your citing of cycle paths is actually confirmation that bikes on existing carriageways is an inefficient use of that road space."

    No l do not follow your logic there can you explain?

    1. For safety, bikes cannot be more than two abreast - which only needs a cycle lane width but on the road still consumes the entire lane.

  4. Lets spend some time on braking which whilst completely irrelevant to congestion as far as l can see. Given the research methodology employed was "(from first reliableish looking google search result in each case)." In this case "reliableish" is not defined so l will give some results from a variety of pages
    10mph - Wet Concrete - 5.81 feet (1.77 m) - which is one of the reasons for my tweet to ask about what type of brakes are use for the figures quoted in the blog post
    The BEST results for each test were:
    Rear Only - 280 inches - 24 feet (7.34m)
    Front Only - 134 inches - 11.17 feet (3.4m)
    Both - 125 inches - 10.4 feet (3.17m)

    Quite a difference between the two, yes they could be dismissed, which is a challange in that same research methodology was used to find these figures. Which was to reiterate "from first reliableish looking google search result in each case"

    Next point which remains l find much confusion in. The amount width take up by a car, is based on the average size of a small vehicle, which is quoted at 5 feet. The Vauxhall corsa l drive is 6.3 feet wide which includes the wing mirrors as l have use them when driving. I am not going to take much issue with that.

    The width required a for a bicycle is 5 feet, please note that is the width required by bicycle. Personally l am not aware of any bike that is the same width as an average small car. Or did l miss read the figures. The 5 feet comes from 1/2 the recommded width of a cycle lane, 1.5m (5 feet). 1.5m (5 feet) is not the width of any bike l am aware of.

    If the same was standard was applied to the car width, the minimumn recommnded width of a road for vehicle is 6m. Half of that is 3m or 9.8 feet, which is just under double the figure quoted in the article 'uses 5' by 17' of road space' which should read "uses 10 feet by 17 feet of road space".

    The most crucial question which remains and will be unanswered is what has braking distances have any relevance to congestion?

    1. A bike is physically smaller than a car, but when being ridden the safety margins around it - braking distances in front and safe clearance each side - make the space required as above - larger than that required for a car.

      I gave my references - your Javascript calculator with no explanation, just figures may as well be a random number generator!

      Reposition the bikes and cars in the photo withb safety taken into account and the bikes will take up more space than the cars.

      Most of the congestion I see caused by bikes is cyclists on single track road's with queues of cars behind. But the blog started from the picture - which is misleading.