The Bicycles.SE blog states "Cyclists are vehicles, not pedestrians.". I think most of this community, plus most of the laws agree with that.
However, a cyclist has the speed, mass and maneuverability of a sprinting person (who is, of course, a pedestrian).
Why are bicycle riders considered vehicles and not pedestrians?
Traffic law (in the US): The law considers the bicycle, first and foremost, to be a mode of transport, and sees a need to regulate the flow of bikes the way it regulates the flow of automobiles. This dates back to the dawn of automobiles, if not before (though in some states it took decades for the law to spell things out as it does). This makes sense, since bicycles can attain speeds well in excess of a normal pedestrian and their speed creates hazards for both them and pedestrians if they ride on sidewalks or otherwise behave as pedestrians.
Besides, if bicycles were pedestrians we'd not be allowed on roads, in the flow of traffic. This would place a major constraint on cycling few of us would want to see.
I believe most states have an exclusion of sorts for children on bikes or maybe even for adults riding at low speed, allowing them to use (most) pedestrian paths. But this is an exception to the general rule.
There is a problem that a significant fraction of the general public does not tend to view bicycles as vehicles, but this is an education problem, and I'd definitely not want to confuse the issue by raising the above question "in public".
(I am reminded, however, of "Big Lip Louie", a guy who lived in rural Louisville, KY 50 years ago when I was a kid. He was, at the time, maybe 30-40, and didn't drive, but walked everywhere. He was tall -- well over 6 feet -- with long legs, and could walk at speeds I'd guess were in excess of 10 MPH. It was fairly common to encounter him walking along a rural road, pretty much right down the center of the road. He was more of a "vehicle" than a pedestrian.)
a cyclist has the speed, mass and maneuverability of a sprinting person
Not really! The world record for 100 m sprint is 9.58 s, which equals 37.6 km/h, which is fast but not anything spectacular for a bicycle. The marathon world record equals to little more than 20 km/h, which is less than my average commuting speed. Going back to "human" speeds, I would estimate that an average biker goes roughly twice the speed of an average runner.
With double speed:
In the UK, the law that says cyclists are vehicles rather than pedestrians pre-dates the automobile. The specific pieces of legislation are:
If any person shall wilfully ride upon any footpath or causeway by the side of any road made or set apart for the use or accommodation of foot passengers; or shall wilfully lead or drive any horse, ass, sheep, mule, swine, or cattle or carriage of any description, or any truck or sledge, upon any such footpath or causeway; or shall tether any horse, ass, mule, swine, or cattle, on any highway, so as to suffer or permit the tethered animal to be thereon;. . . every person so offending in any of the cases aforesaid shall for each and every such offence forfeit and pay any sum not exceeding [level 2 on the standard scale], over and above the damages occasioned thereby.
Regulations for bicycles, &c.
bicycles, tricycles, velocipedes, and other similar machines are hereby declared to be carriages within the meaning of the Highway Acts
The decision to put bicycles in the same category as horse drawn carts seems perfectly sensible given the era in which it was made. While the situation on the roads is now very different, cyclists should still be classed as vehicles rather than pedestrians for the reasons given in the other answers to this question.
I'm going to try to answer the question about WHY are bicycles are considered vehicles rather than listing the multitudinous local laws that say as much.
The justifications that I see are:
Historically I expect it's because bicycles are machines and they behave more like other vehicles than they do pure pedestrians. I suspect the law developed in most countries in a simlar way to the UK as described by Tom77 in his answer. Originally power came from people and draft animals and the speed range was between ox carts and galloping horse riders. But a galloping horse is a fragile thing, so riders tended to be careful because if the horse falls the rider is likely to die. Note that this is the opposite to a motor vehicle hitting a pedestrian. But a horse at a walk or trot can move off the road and walk around a relatively slow-moving pedestrian or cart. So you had the pragmatic situation that pedestrians were expected to move out of the way of horses, everyone waited to pass carts until it was physically possible, and important people yelled a lot.
I expect that the formalisation went "the faster you go the more you have to avoid other road users. This is therefore the law".
Bicycles are surely vehicles, since people "ride" them, they don't walk with its aid. Then, the bicycle would be considered a land, inline-two-wheeled, human-propelled vehicle.
In Brazil, where I live, the (sometimes confusing) Traffic Law states that bikes:
It is interesting that traffic laws and regulations have two ambiguous functions: at the same time they force vehicles to follow rules, so as to "protect" the rest of society, it is possible to see a tendency to create traffic laws so as to facilitate motorized traffic, and someway put the rest of society "out of the way".
Using the bike for transportation, in this context (partly vehicle, partly "human") has been an interesting way (for the good and for the bad) to feel how difficult it is to "label" it one thing or another.
Pedestrians (though not sprinters), wheelchairs, and pedestrians using walkers are statically stable, while cyclists are dynamically stable (with the exception of some fixie freaks).
Locomotion is defined to be the act or power of moving from place to place. Statically stable locomotion has the added constraint that the moving body be stable at all times. In other words, if the body were to instantaneously stop all motion, the body would still be standing. More specifically, the vertical projection of the center of gravity will be contained within the convex hull of the body's points of contact with the ground at all times.
Since pedestrians often assume that others can stop on a dime, they make sudden directional changes without thinking about what's around them. Mixing pedestrians and cyclists on narrow sidewalks where cyclists can't reroute is a recipe for collisions.
In normal conversation, a bicycle is a vehicle because it is a machine used to move people or cargo.
From a legal perspective, whether or not a bicycle is considered a vehicle depends on local law. Defenitions are used in laws to develop the scope of a law and in what situations it applies. It might be convenient to have separate definitions for vehicles and bicycles.
However, if your local jurisdiction does not consider a bicycle a vehicle, it still may be legal to ride a bike on the road with all the same legal rights and responsibilities as a automobile.
For example, in Michigan, bicycles are excluded from being vehicles (Michigan Vehicle Code 257.79) because they are human powered. Bicycles get their own definition in the statute (MVC 257.4). Bikes can still ride on the roads of Michigan with all the same rights (MVC 257.657).
It is worth noting that Michigan's definition of a bicycle includes tricycles. Legal definitions don't always match dictionary definitions.
Many cities in Canada do not allow for cyclists to mount their bicycles on pedestrian walkways, and must ride on the road in the flow of traffic, on designated pathways, or in bike lanes. Pulling over to the shoulder to allow traffic to pass is permitted. This is enforced by both local bylaw and policing services, as well as the RCMP (I know this through experience). Thus by Canadian law, the bicycle is considered a vehicle (with unique exceptions, such as not requiring a licence/insurance), and not a walking aid.
Edit - I personally asked a RCMP officer this question, and the best response they could come up with was "most bicycles are capable of attaining and maintaining road limits, as well as the prohibition of riding on sidewalks to protect pedestrians forces the bicycle into the flow [of traffic]." Additionally, the cyclist "shall allow other traffic to pass at regular intervals where safe" if they cannot keep up. However, the cyclist can occupy a lane if the limit cannot be held, assuming the impediment to, or overall volume to traffic is minimal. If those cannot be met, the bicycle shall not be ridden.
A bicycle is considered a "vehicle" and is supposed to obey the same traffic laws as a motor vehicle...stop signs, turning lanes, signaling a turn, etc.. A bicyclist of average health and condition could ride a bicycle 50 to 100 miles in a day without too much of a problem. An average pedistrian, walking or running, could not likely achieve those same mileages. In Ohio, a bicyclist has the right to actually occupy a complete lane of travel when necessary. I've only seen a cyclist do this one time, and he was holding up traffic for about 4 blocks! It's no wonder with antics like this that drivers get upset with a bicyclist. Just because you have the right to do this, doesn't mean you should use that right! I prefer to stay as far to the right as possible, only moving to the center of the lane to execute a left hand turn. Creating harmony is much better than causing friction!
My understanding of the law in the UK is that a bicycle is a vehicle (meaning that you must cycle them on the road and not the pavement, not that anyone around here seems to obey that particular law), but they are not motor vehicle, meaning you don't need to pay road tax, hold a license, are exempt from speed limits (but can still be pulled up and fined for dangerous cycling which can include excessive speed) and don't need an MOT certificate to prove your bike is roadworthy.
I am not a legal expert, however, so the usual disclaimers apply.
My opinion is that they're considered vehicles because getting hit by a fast-moving bike is a much bigger deal than being hit by a sprinter! Also, a pedestrian can come to a stop and not fall over, whereas a cyclist needs to put their leg out, hold onto something, etc, to keep from going over when stationary.
Walking aid? Bicycle is not a couch, it has wheels so it is a vehicle and as for speed well that depends on the rider. Personally I have never seen a person doing 60 kilometers in 2 hours. Of course sometimes you go slower say when uphill or against the wind but so do other vehicles, you wouldn't call tractor a walking aid?
