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Comment by cortesoft | Hacker News Reader

I think you have a fundamental misunderstanding about how people drive. People don't look at a speed limit and then drive 15 over; they drive the speed they feel comfortable with, regardless of the speed limit. Studies have shown this:

Q. Wouldn’t everyone drive faster if the speed limit was raised? A. No, the majority of drivers will not go faster than what they feel is comfortable and safe regardless of the speed limit. For example, an 18-month study following an increase in the speed limit along the New York Thruway from 55 to 65 mph, determined that the average speed of traffic, 68 mph, remained the same. Even a national study conducted by Federal Highway Administration also concluded that raising or lowering the speed limit had practically no effect on actual travel speeds

https://www.motorists.org/wp-content/uploads/2015/05/speed-l...

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> they drive the speed they feel comfortable with, regardless of the speed limit

My anecdata does not support this. When roads are not congested, I can see that most drivers accelerate from ~70+mph to ~80+mph right ofter the speed limit sign changes from 60 to 70.

Yes, because they are comfortable at higher speeds than what is posted. Just that they'd rather only drive +10mph of what's posted to avoid speeding tickets.

I think what you're seeing is that most people know that up to 10mph over the limit is pretty safe in regards to getting a speeding ticket.

That's separate from how fast they think is safe on the freeway in general from a physical standpoint. If there were no limits posted, they'd go even faster.

So basically I'm saying that both you and the parent poster are both correct. It's just that more than just physical safety is being taken into account.

The claim that the average speed at which people drive depends on the speed limit, and the claim that it does not, cannot both be correct.

They're both correct, or both wrong, in that both of their reasonings are correct in having a noticeable effect on thd outcome, while their conclusion may not be.

I wonder if there is some kind of "steady state" vs "transition" effect that could explain this though. For instance, if you put up a sign that changed the speed limit from 70 to 80 but changed nothing else about the road, would you see an initial increase and then decrease after a few miles? Although I'd also guess that in reality if the speed limit changes to 80, there's probably other characteristics of the road that change so that the steady state might not regress back in this instance.

Usually when the speed limit bumps up from 55 to 65, it means the stretch of highway is actually more safe. Whether it is a long straight away with few on/off ramps, or the end of construction - the jump in speed limit usually does correspond to the level of safety of the upcoming stretch of roadway.

Well, they have a speed they're comfortable with, AND an amount over the limit by which they feel (legally) 'safe' at.

All this proves is that they don't want to go much more than 10 over the limit, AND the speed at which they feel safe is at least (but maybe higher than!) 80mph.

As somebody who is ideologically predisposed against speed limits, bullshit.

If you've ever gone much faster than is customary for a road (say 110mph following a cop), and then slowed down to say 90mph, it will feel quite slow. If you then don't set about consciously lowering your speed, you will even find yourself creeping back up.

Humans are notoriously bad at perceiving what-if dangers and being aware of our own limitations. The level of difficulty we perceive is what's required to keep up with the expected - road curves, passing other predicable cars, etc - not because we're anticipating surprises.

Another example is outdriving one's headlights - either the sheer amount of deer that get hit, or when you flip on your high beams in a fog and actually become aware of how little you could see.

As someone who's driven over distances that had notably higher speed limits (EG 75 MPH in extremely rural areas), I have found that /in those areas/ the speed I went //without// looking at the dashboard was more or less very close to the actual speed limit. I was actually driving at the real speed that is safe for a typical small car on such a road in 'ideal' conditions.

Were you able to reproduce this effect on analogous 55mph/65mph roads? Are you sure you aren't just used to driving 75mph on highways in general (ie you're not from Seattle), and found speed limit signs that actually matched?

Driving through rural areas you must have experienced the sudden ~30mph sign, signifying a town coming up. Did this "drive what you feel" approach line up there too? When the town was at the bottom of a hill?

For context, I've done around 25k miles cross-country non-interstate. I've concluded that what the individual states choose to sign as the general maximums has more to do with local culture and politics than with general terrain.

You've thrown out quite a number of different topics, and some of the questions you're asking might also lead anyone who can contribute to a discussion about speed limits being set at safe speeds to admit to having committed what is currently a crime because of an incorrectly calibrated "limit".

With respect to the engineering safety of the sudden 30mph sign (which I assume is in a rural area on an otherwise small highway); yes that sounds like you're describing what is typically called a "speed trap". A real traffic safety engineering standard SHOULD call for a clearly posted and graduated reduction in speed as approaching the town at a /bare/ minimum. However, a true engineering solution would isolate the town and the highway entirely. The point of the highway is to be a high speed transit corridor and it is inefficient and unsafe to route such a thing through a dense residential or commercial area. Instead there should be an exit system that leads off to a side path for such a town. I would prefer an actual barrier that encloses the typical route and possibly caps or bridges over it (maybe with a park) for existing situations that have developed in days with less good planning. In any such cases a designated detour route should also be constructed such that it is possible for "oversized loads", emergency response teams, and post disaster travel to route around failure in the now enclosed sections.

My examples are pointing out possible edges of feeling safe equals safe envelope. And I don't think cops hang out on HN looking for anecdotes of speeding to investigate, nor are you going to get a black mark on your permanent LexisGoogle record from admitting that you have sped.

There are plenty of towns large enough for highway bypasses and traffic lights. The ones I'm talking about have one good road, maybe two if they're lucky enough to be the intersection. I indeed appreciate when there are graduated signs so I don't have to use the brakes, but this obviously costs money they don't all have, and isn't needed by people who already know the road. Talking about traffic engineering is laughable for such places - if your goal is to pass through as quick as possible, you could just take the interstate.

The only reason they do it with a single sign instead of many is because the town is a speed trap funded city.

If there was not revenue generation, if the fines were required to go only in to the state or federal general budget, I believe the situation would shift towards one of the safe engineering solutions I outlined above instead of the revenue generating status quo you see today.

I agree that people will tend to not drive faster than what they feel comfortable at. I have even heard stories about places around my old town where they drew the lanes closer together (width and lane length) to make it feel like you are going faster to get you to slow down and it has had positive effects on how fast people drive.

However, people have vastly different "feelings" for what is comfortable. I've been in multiple different driving experiences in an awd subaru where I was going 30 under the speed limit because the weather was terrible and people were flying past me in their 2wd cars.

Shit, I even had an experience where I and literally 75% of other cars full on stopped on the side of a highway with our hazard lights on because we couldn't see more than 200 feet in front of us and people were still driving 30 mph past us. I shit you not that was one of the scariest moments of my life because as the visibility got worse and worse, everyone starting putting on their hazard lights and going like 30, most cars turned off but we thought it was OK until the rain and fog got so bad the cars in front and behind us completely disappeared in the grey rain/fog. We drove for about a minute going like 25 MPH (I was slowing down to get more comfortable because I was freaking out) and I risked turning off onto the shoulder preying I didn't randomly ram one of the cars pulled off and we got lucky and were able to sit their until it got better.

I don’t think dismissing the parent comment based on a study is fair. Anecdotally, I drive the way the parent describes, and several comments also corroborate with that. Likely that a non negligible portion of the population drive this way.

I don’t think dismissing the parent comment based on a study is fair.

Well, there's a surprising turn of events on HN: an appeal to discard the findings of a study in favor of one poster's suppositions, and another's anecdata. :-)

The irony is def not lost on me ;)

If you look at the studies, they actually show this. There is a small percentage of drivers (something like 5-15%) that always try to drive at the speed limit, even if that is lower than the speed they would naturally drive at.

This is one of the reasons experts argue that you NEED to set the speed limit at the natural speed people will drive at; otherwise, you will have a big speed difference between the majority who drive at the comfortable, faster, speed, and the 15% who are driving slower at the speed limit. You want the two groups to drive at the same speed.

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