[phalf]

It's even great in the sense that a speedometer tends to make people aim for "I need to go 65 mph" instead of "I should not go above 65 mph" which a speed limit is actually intended to mean. The speed limit became a target instead of being a limit.

[gjm11]

Traffic flows more smoothly when everyone is going at about the same speed. To achieve this without communication between vehicles, you need some "obvious" speed for everyone to try to drive at. In many contexts the speed limit fits this need pretty well.

There are situations where it doesn't. These are mostly also situations where the speed limit doesn't work terribly well as a limit either. For instance, bad weather or winding roads may mean that driving at or near the limit is unsafe. In that case, sure, it's not good for everyone to coordinate on driving at the speed limit, but it's also not good for everyone to think of the speed limit as the right upper bound for driving to be safe.

So I think that in most situations either (1) treating the speed limit as a rough target as well as a limit is mostly a good idea, or (2) the speed you try to use as a limit should be something other than the nominal speed limit.

[mitthrowaway2]

Vehicles can all synchronize speed independently based on a well-tuned control law while observing only the distance to the vehicle in front of them. So looking out the window is sufficient for that, if the drivers are not terrible.

If driving at the speed limit on a winding road is unsafe, the speed limit is probably too high for that road. But in practice, it's complex, winding roads that cause people to drive at reasonable speeds, rather than numbers posted on signs.

[Arch-TK]

The speed limit being a target is how it is treated in driver education and tests in the UK.

You can fail a driving test if you spend too much time driving more than ~5 miles per hour below the speed limit in safe conditions.

[tristor]

This is largely because speed limits are too low. In safe conditions, most roadways are built in such a way that a modern vehicle can safely go 10-20mph over the speed limit without difficulty or increased risk. There are several reasons for this.

The point though is that timidity in a driver is actually more dangerous than exceeding the speed limit. Being consistently below the speed limit is a strong sign of timidity.

[gmac]

I think this is overstated.

My driving instructor was (rightly) very hot on the principle that you must always be able to stop within the distance you can see. Speed limits are not set with this in mind.

In the UK, for example, that means that on winding country roads you should often be doing a lot less than the 60mph speed limit.

[tristor]

I agree with your instructor. That said, modern cars can stop in /much/ shorter distances than previously, largely thanks to improvements in tire technology.

Nearly every production vehicle available today can brake from 60mph in less than 140ft, more performance oriented vehicles can do so in under 120ft. The standards for “safe stopping distance” used in the US triple this distance to account for slowed reaction time because drivers are not attentive.

Realistically less than doubling these figures is correct for attentive drivers. 60mph is 88 feet per second, and 1 second is plenty of reaction time for an attentive driver, meaning 200-240ft total stopping distance, closer to double the distance the vehicle is capable of rather than triple.

So if the visibility is less than 200-240ft, you should be going slower than 60mph. 240ft isn’t very far in a car though, it’s roughly the distance traveled in 3 seconds at 60mph. There’s certainly some country roads I’d slow down on, but if you’re paying attention you’re well good on most.

For what it’s worth, the average reaction time of a gamer is 150ms, so a full second is plenty of margin of error.

[midasuni]

U.K. stoping distance is 240ft at 60mph, 120ft at 40mph. 75ft at 30.

[phalf]

> the average reaction time of a gamer is 150ms

It's rare that those gamers have a crying toddler in the backseat while being sleep deprived and the sun coming from a less than perfect angle.

[InSteady]

Also not generally being surrounded on all sides by other unpredictable gamers whose own split-second reactions are going to determine what their safest move should be.

[panragon]

I don't think it's so much about the timidity of the driver, it's the effect on driving slow has on people behind you. Driving below the speed limit increases the amount of drivers who need to do overtaking, which are moments substantially more dangerous than just driving straight. If it weren't for forcing other people to overtake I don't think we'd really care, even if it was a sign of timidity.

Very common to see older people drive slow on the highway because going 100KM/h seems scary to them. This is, of course, absurd, since driving 80KM/hs on a 100KM/h road causes way more moments for bad things to happen because you're forcing everyone to merge into the speed lane, including trucks with bigger blind spots, rather then only the drivers choosing to go above the speed limit. If you do this you should absolutely be fined, and that's not because it's a good metric for timidity (which I agree can be bad for drivers in general), but rather that the action itself causes harm.

[phalf]

> Driving below the speed limit increases the amount of drivers who need to do overtaking,

Nobody "needs" to overtake or is "forced" to doing something dangerous outside safe margins. Seriously, this is blame shifting when somebody does something stupid. When you do, it's 100% on you.

100km/h on a highway with everybody otherwise going 130km/h is rare. This is about a 65mph road (100km/h?) where somebody goes 95km/h and everybody behind them goes berserk. That's an attitude that needs to change, not by the 95km/h driver, but by everybody behind. Going 100km/h is not a right, does not force you to do stupid overtaking maneuvers and the time you lose by going 95km/h is negligible. At least it's substantially less than you'd expect, since there are many other factors that slow you down on a journey. You rarely drive for 3 hours straight, no interruptions, no other traffic on the road. Even if you did, doing 100km/h instead of 95km/h would get you there by 9 minutes earlier. That's the upper limit here, but you are likely going to save less than 5 min. After 3 hours.

[tristor]

We (for some measure of we, but at least the US and most Commonwealth countries) have laws against this. It's called "Impeding the Flow of Traffic". As far as it matters, you are absolutely and directly wrong about your statement here. It's the 95km/h driver that needs to change.

You seem to have an agenda in your comments here, and in some of them I think you have a point, in this one you are overplaying your hand.

[phalf]

50mph on a 65mph road may be "impeding the flow of traffic". 63mph certainly isn't.

I'm a bit confused regarding your insinuation of an "agenda" in my comments? I've been in enough situations where somebody behind me or others on the road was endangering everybody just because the car in front of them wasn't going the $safe_margin_above that they were expecting of everybody. So they go like 3ft behind them and put pressure and stress on people. It's a dangerous mentality that can get people killed. It's not the "slow person" (going at 63mph) that's the danger in that scenario.

[InSteady]

I personally find GPs agenda of promoting patience, common sense, and safety on the roads to be both dangerous and offensive. That kind of mentality is only a hop and skip away from becoming a deranged anti-car environmentalist.

[phalf]

> This is largely because speed limits are too low.

Research is clear. For every 5mph increase on a highway you can calculate how many people per year per mile will die more.

If you want more people to die, then sure, speed limits are too low.

[midasuni]

In the U.K. the motorway is by far the safest type of road. https://www.driving.co.uk/car-clinic/advice/are-motorways-sa... Etc

Could you point to your research.

[zanellato19]

> The point though is that timidity in a driver is actually more dangerous than exceeding the speed limit.

This is a bizarre claim, since most accidents/deaths would be avoided by cars being slower. Unless you have data on this, this is just "I like to drive faster" with more words.

[tristor]

Nearly every study on the topic has concluded that faster vehicles get into less accidents, but the accidents they do get into are more likely to be fatal. Conflating accident rate and fatality rate means you can’t see the forest for the trees.

At any rate, neither statistic has anything to do with my claim. Timidity is dangerous because it’s unpredictable and creates a rolling roadblock. The most dangerous thing while driving is /other drivers/. Being able to predict their behavior and avoiding having to overtake both greatly reduce risk. Timidity increases both of these risks significantly.

[phalf]

> Nearly every study on the topic has concluded that faster vehicles get into less accidents

Citations definitely needed. Not just of the studies that perhaps support your point, but of the reviews that do a quantitative overview of that the majority of studies conclude what you claim. Everything else is "I want to drive fast, slow grannies out of my way".

[zanellato19]

Fatal accidents are so more impactful than non-fatal accidents that saying people should drive faster is absurd.