It's a bit of a tangent, but all the roads I've seen labeled 30mph or 35mph would be quite safe to take at 45. The flow of traffic is 5mph over anyway. But this is with residential roads universally at 25mph. I'm not sure what kind of road he was on.

I used to think like that when I was young. Then I learned I was short-sighted, and that every time there are traffic rules (including speeding) they (almost) always make sense. Sometimes they don't, true. If you then have contacts within the (local) government they love to get proper feedback from citizens.

To give an example: there's a school nearby where the sign says 30 km/hour. It is an important road people who live in my neighbourhood, connecting them to their home (commute, shopping, etc). I drive on my bicycle crossing that road. Do I assume people drive 30 km/hour or 50 km/hour? Cause many people drive 50 km/hour there. When kids go to/from school people might drive 30 km/hour, I don't know exactly how that works. Many might not even know there's a school there. Even though the sign says there is, perhaps that gives the mental note: "..but it is Saturday." If we're going to arbitrarily ignore traffic rules whenever we see fit, it is going to lead to chaos.

Urban speed limits aren't set by what speed your car is safe to drive at, but rather what speed is safe that you're less likely to hit pedestrians and other cars.

A road has to be designed a certain way based on the speed. You can't just put up a speed limit sign, and speed limit signs are very often not based on what's safe.

You don't seem to be addressing the criticism of your argument, which is that urban speed limits are determined by likelihood of collision with another car, a bicycle, or a pedestrian in the event of an unexpected need to brake hard. This depends on more than just the physical engineering of the road.

There are lots roads with the same environment or with environments less likely to lead to collisions with cars, bicycles, and pedestrians that nevertheless get lower speed limits.

This isn't the case in New Zealand. It's normal for all rural roads in New Zealand to be posted with a 100 km/h limit, with speed recommendations (not limits) on the corners.

Even winding mountain passes, which wouldn't be possible to take at 100 km/h without a race car will still have a 100 km/h limit. It's up to the driver to make a judgement as to how fast they can safely drive.

How do you determine "safe to take at 45"? Kinetic energy increases quadratically to speed, so your braking distance is much larger and doesn't scale linearly to speed so, no, just because you feel your car can safely take those roads at 5-10mph over the limit doesn't mean it's safe, the environment dictates the speed limit, not the road conditions per se.

> How do you determine "safe to take at 45"?

I look at the roads that do have speed limits of 45mph.

> the environment dictates the speed limit

Yep! And the roads I'm talking about are built in the same way with the same environment as the 45mph roads.

I'll back down my "all" to about "90%" though, I remembered a short road where 35 actually fits.

But in general, if we accept that the 45mph roads are actually safe at 45mph, then there's a lot of 35mph roads would be equally safe at 45mph.