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 1sqM 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).