Aside from the issue of pure legality, which means that you can have legal penalties imposed for violating a speed limit, there are valid reasons for such limits. The faster you are driving, the less time you have to react to anything that is happening in terms of what other cars or pedestrians may be doing. And if you do have a collision, it will be more damaging at higher speeds. So speed limits are designed to be appropriate for the driving conditions of a particular road. And in view of the tremendous number of people who are killed or injured every day in traffic accidents, speed limits (and other rules of the road) are worth taking seriously.
That's completely unrelated. Light usually slows down when passing through ANY matter. It does not react with dark matter (which is what makes the "dark matter" invisible in the first place), except through the gravitational interaction. The "cosmic speed limit" is a limit on how fast ANYTHING can travel (matter, energy, or information); it is just conventional to call it the "speed of light". This speed limit is for a vacuum - the assumption is NO normal matter, and NO dark matter; the presence of any matter may slow light down slightly.
That is a matter of local law, and will vary between jurisdictions.
I doubt many people could walk the speed limit. Maybe in a school zone where the limit is 15 miles per hour. However, since the speed limit is a maximum, it doesn't matter.
Matter can travel at any speed you like, if you can pump enough energy into it.The only limit is the speed of light. If you can supply it with enough energy, thenyou can make the matter move as close to the speed of light as you want it to,but there is not enough energy anywhere to make it move at the speed of light.
It's not that there is a speed limit, but you can't go to the end of the runway. For most passenger airliners, takeoff speed is about 135 to 155 knots. It's just a matter of how long it takes the plane to accelerate to that speed.
826 limit
the posted speed limit
When another speed limit sign is reached that changes the limit from the previously posted one.
The speed limit in the fast lane is the same as the speed limit for the road or highway you are driving on.
The speed limit is exactly that - the speed limit. While a reasonable excess of speed might be overlooked when overtaking another vehicle, there is no guarantee. You can be pulled over and cited for speeding, still.
The posted speed limit is the max speed.
In the UK the speed limit comes into force as soon as you pass the speed limit sign. As such the distance is zero as you should have slowed down to the posted speed limit before passing the sign.