[SoftTalker]

> a road that's labeled as 45MPH zone, but is treated as a 65

If this is the case, then the speed limit is too low. To control speed on such a road you either need draconian enforcement or you need to change the road so people aren't comfortable driving that fast. Make the lanes narrower, introduce lane shifts or reduce the number of lanes, etc.

[milkytron]

A large problem in speed limit setting is that 85th percentile is used many times for setting the speed limit and other factors are ignored or aren't weighted as heavily.

It's a very fuzzy practice, and I think as we continue towards an automated driving world, we need to be more critical of how speed limits are set.

Using the 85th percentile as a means to determine speed limits ends up with 15% of all drivers exceeding the speed limit, or worse, more drivers exceed the speed limit than those original 15% because they know consequences may be rare.

https://www.ite.org/technical-resources/topics/speed-managem...

[kube-system]

Sometimes bad road design (e.g. lanes too wide) are to blame, but in miserable neighborhoods with no traffic enforcement at rush hour you can also end up in a situation where the majority of people on the road are simply aggressive drivers who are familiar with the road. At some point you do need to enforce the law if it isn't being respected. There is a growing subset of people in the US who not only disregard traffic law but pride themselves in a distain for it.

[pavel_lishin]

> If this is the case, then the speed limit is too low.

I don't disagree with you, but it's still a problem if there are drivers on that road who are driving so slowly as to be unsafe, robot or human.

[threetonesun]

IDK if it's draconian but speed cameras or simply forcing cars to have modules that report speeds at certain points and issue fines automatically should be standard by now. What's the point of having smarter cars if they can't be forced to stay below the legal speed limit.

[kube-system]

I don't think building enforcement into cars would be a good idea, or even effective, but a few speed cameras work wonders for changing the overall 'temperature' of driving in an area.

[threetonesun]

How would setting the max speed of a car to the speed limit be a bad idea.

[kube-system]

Falsehoods programmers believe about speed limits:

1. The speed limit of a road is always marked by a sign

2. The speed limit of a road is in a database

3. You can look up the GPS location of a vehicle to determine what road it is on

4. Roads have exactly one speed limit at any one moment in time

5. Speed limits rarely change

6. Well, maybe speed limits do change, but only during certain fixed times

7. Roads have speed limits

8. Cars are only driven on roads

9. There are no exceptions for following speed limits

10. Well maybe there are but we can safely ignore those without any real consequences

[...]

I've personally done some software experimentation with speed limit detection in vehicles. The combined accuracy of automatic-traffic-sign recognition and speed limit databases + GPS is far less than 100% in real world driving conditions.

[SoftTalker]

I would call speed cameras draconian.

There's a road near me that just dropped the speed limit to 40. This is a divided road, two 12-foot lanes in each direction, good visibility, with turning lanes at intersections. It's highway-class. Most people drive 55 or 60, because that speed feels appropriate and reasonably safe (search the "85th percentile" rule in setting speed limits to read more about this).

By reducing the speed limit to 40 the road is IMO less safe, because there are always some people who very conscientiously do not exceed the posted speed limit. So now you have some people driving 40, while most people still want to go 55 or 60. This creates an unsafe mix of vehicle speeds.