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Comment by wvenable | Hacker News Reader

What makes a road a 25mph road? One dangerous enough that people don't feel comfortable driving faster -- how is that a solution?

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Yes, basically. You make traffic lanes narrower, with much wider shoulders that are textured to discourage use. If there are bike lanes, you separate them with rounded dividers. Trees in the center divider also help. As do curves, and bumpouts around on-street parking.

People will just drive over textured bumps, I've seen it. You need to design the road such that people will damage their vehicle if they drive dangerously (things like on street parking, concrete bollards, tall curbs etc).

Those are good points. Bollards, tall curbs, etc are appropriate for urban streets, because they protect pedestrians on sidewalks. But curbs are hazardous to bicyclists. More generally, you want streets that seem more dangerous than they actually are.

> But curbs are hazardous to bicyclists.

You can easily cut a bypass through the curb or chicane.

True. I've gone down hard, though. At night, they can be hard to see.

In neighborhoods near me we have gently sloping curbs. They are about a foot wider than the normal 90 degree curbs I see in more dense urban areas. It is easy to notice from the car if you pull partially up onto them. I suspect it also makes it slightly easier for cars to go of the road, but that hasn't been a real problem. Cars, bike and people seem to be at less risk from the curb directly.

"seems more dangerous" probably only works for so long... Surely people would get used to the "dangerous" streets and realize they aren't as dangerous as they seem.

Bollards 3, bozos 0. [1]

The Sidney Harbor Tunnel had a serious problem with oversized trucks getting wedged in the tunnel. Watch a truck drive past two sets of giant flashing overhead warning signs. They stop only when they reach the final sign at the tunnel mouth, a water curtain with a giant STOP sign projected on it.[2]

[1] https://www.youtube.com/watch?v=i_Cw0QJU8ro [2] https://www.youtube.com/watch?v=pRKA7m-tbqM

That water screen is really brilliant.

An earlier bridge for them to crash into will also do the job quite nicely.

To be nice make it out of crumpling noisy material, not concrete.

> An earlier bridge for them to crash into will also do the job quite nicely.

Except for the part where it requires significantly more maintenance to fix up the bridge and it's incredibly dangerous for drivers following, whether the truck hard-stops or gets its top sheared off.

Hanging bars seem to solve this problem. Makes a loud terrifying noise when you hit them, but doesn't leave any permanent damage.

Truckers may not notice if the problem is at the rear trailer, as it was in the video. The water curtain, although unusual, is not expensive. It's just a sprinkler pipe and a very bright slide projector.

Also, it's at the start of a blind curve -- the road design naturally leads you to slow down as you approach, so stopping short be won't be as much of a problem.

You could think this way: When you are driving at day on a parking lot full of cars you drive slowly, right? And when you drive on a empty highway you drive fast. Regardless of law or street signals, you would drive at this same speed, right? Why? Because the environment are different. This is the point of the article. We have been giving tickets since forever and yet nothing has really changed, and nothing will change, unless we started to design the roads with the speed they need to have.

Yes but I don't see how making every road as safe to drive in as a parking lot (i.e. not very safe) vs. a big empty highway is a solution. The problem we're trying to solve is safety, not speed. Slowing people down by making roads less safe misses the point.

A neckdown or narrow lanes do not make a road less safe. Instead we see the opposite, traffic naturally slows down and thus the road becomes safer.

They also make the road less useful -- you have to balance safety with something. If not, it's just safer if everybody stays at home.

If the road has to close because of a traffic accident, that makes it less useful too - especially when it seems to happen almost every day. A road with less throughput that at least keeps moving can be better.

>They also make the road less useful

And that's the real goal here. This is just another avenue of attack for anti-car zealots.

You say "anti-car" like it's a bad thing.

I guess it depends on if you value freedom of movement or not.

But thanks for dropping by as an example.

I value freedom of movement - but not only through car accessibility. I value being able to walk / bike / take a bus safely and within a reasonable distance from my destination. The modern American suburb is terribly designed from this perspective.

This is not an uncommon opinion: https://likewise.am/2016/05/08/why-suburbia-sucks/

I'm a pedestrian. Many roads around me have been made more useful to you, to the point where they're useless to me. If they're all made useful, then I'll be the one who has to stay at home.

Traffic calming doesn't make roads less safe.

Advocates of traffic calming measures aren't trying to literally make roads as unsafe as parking lots. What makes parking lots unsafe is the constant threat of someone pulling out in front of you, no one is advocating simulating that.

Think about roundabouts, they force you to slow down because they prevent you from driving directly though an intersection. They are statistically much safer than 4 way stops.

I agree that neighborhood roads should have roundabouts and so on. But that doesn't apply to major arteries, highways, etc.

I would agree, but my father used to drive a bottled water delivery truck. And he's seen lots of neighborhoods where roundabouts are simply not built large enough to accommodate anything with more than two axles. In California, roundabouts tend to be added into new construction, but squeezed into a space that is no larger than a normal intersection.

If they're designed properly, they should be low, almost the same height as speed bumps. That way something with 16 wheels can go straight over them while regular cars will probably go around them.

>Think about roundabouts, they force you to slow down because they prevent you from driving directly though an intersection. They are statistically much safer than 4 way stops.

That's not entirely true, with half decent vision I can drive straight onto and off the roundabout again. Certainly in a 30/40mph limit I don't have to slow down particularly. The point of roundabouts isn't to slow people down, it's to keep traffic moving efficiently and safely.

Four way stops are just obviously an awful solution that I've never understood

Depends on the size of the roundabout, some are designed for 40 mph others for a more sane 20 mph.

I mean, a roundabout is a system for efficient "giving way". 20mph is only "more sane" when a roundabout is in a low speed limit area. We've got plenty of them on 60mph zones - you've got no interest in having cars slow down and accelerate again when not necessary (if nothing else because it's a waste of energy as well as time).

How is it efficient for "giving way"? If one entry is highly traficated, entries between the traficated one and the popular exits cannot get in.

The second benefit of well-made roundabouts is that they impede head-on and T-bone collisions. All accidents become side-by-side accidents.

By god, I hate roundabouts. Not because I have to slow down. If your exit is 45-90 degrees to the right (which a few of the roundabouts I have to go through are), you can commonly go in a straight line towards it without slowing down the slightest anyway, and going in as straight a line as possible is encouraged over here to make your intentions clear.

However, I feel much less safe going through a traficated, small-radius two-lane roundabout than I do going through a traficated intersection (making a turn or not). First of all, you have to find a gap, which is stressful and entirely unnecessary in a normal intersection. Traffic usually mean that just don't get a large enough gap to get in without accelerating hard, which isn't really safe. If you want an exit that is not the first (sometimes also the second), you have to use the inner lane, meaning that you need to find a gap in two lanes, rather than one. It seriously lacks some fair scheduling.

Depending on the roundabout, exiting can only be done by going "LEEROY JEENKIIIINS". Your mirrors point at nothing useful due to the turn of the roundabout, so the lane change back out involves going fast forward to the left, with your neck twisted as far as you can back to the right. Everyone is moving at their own random, highly variable pace, so a quick orientation is immediately invalidated. On a straight road, you can rely almost entirely on your mirrors so your peripheral vision still covers what's ahead of you.

Collisions between cars are likely milder, as the vehicle velocity is limited by the roundabout geometry, but side collisions are awful, and the chance of collision seems much higher, feeling like a game of Russian roulette. I'm normally (over)confident behind the wheel, with no problem driving like an idiot, around other driving like idiots, and have several hundred thousand kilometers of driving experience, but I get uncomfortable and stressed in those roundabouts.

Some two-lane roundabouts have fixed this by drawing the lines so that the lanes spiral out, with the outer lane going to the next exit, and the inner lane going to the one after it. In this way, going around the roundabout is a constant lane change to the left with no one beside you, and an exit is simply keeping your lane. This helps a lot, but is by no means common. Entry still sucks, though

>Collisions between cars are likely milder, as the vehicle velocity is limited by the roundabout geometry, but side collisions are awful, and the chance of collision seems much higher,

One study of 17 intersections found an 84% reduction in injury accidents. And a 100% reduction in fatal accidents. And every study I've seen is pretty similar in terms of injuries avoided.

Hmm. Those seem like very solid numbers. I wonder how the total accident count compares. Scratched cars are of course not important in comparison to a human life, but I'm curious whether my gut feeling of not being able to obtain an appropriate overview actually translate to accidents.

Fatal traffic injuries are quite rare over here (175 in 2015, which gives about 1/4th of the fatal injuries in traffic per capita of USA), with most seemingly being bicycles killed in intersections by trucks turning right in the city (We have far more bicycles than cars, and they seem to enjoy ignoring rules while simultaneously going "I HAVE THE RIGHT OF WAY AND PRIORITY OVER MOTORISED VEHICLES, SO I SHALL PROCEED BLINDLY").

I might be underestimating the intersection problem as a result of our "gentler" traffic (I don't recall ever actually seeing an intersection incident - I mostly see two-car incidents on the highway, where some idiot is too busy on their phone to see that the car in front is braking).

> Traffic calming doesn't make roads less safe.

It absolutely does when you measure it against the alternatives instead of the status quo.

The only way you can get an apparent benefit from it is through people overcompensating for danger. People are driving 30MPH, you add some danger, people overcompensate for the danger by driving 25MPH, so the result is as though people were driving 28MPH on the original road. You call this a benefit.

The problem is that it's crazy. You're designing an intentional safety reduction and paying the full cost of it just so that people will overcompensate for it.

What you should be doing is designing a safety improvement that people will undercompensate for. Make the road as safe to drive at 35MPH as it was at 30MPH, but don't make that fact obvious, so that people only drive 2MPH faster even though the road is 5MPH safer. Then people drive 32MPH and the safety level is as though they were driving 27MPH on the original road. Compared to traffic calming you have a safer road and people get where they're going 7MPH faster.

Safer for drivers - maybe. Safer for pedestrians? No.

Traffic calming isn't decreasing the safety of a road, it's decreasing the perceived safety of driving at higher speeds.

>Make the road as safe to drive at 35MPH as it was at 30MPH, but don't make that fact obvious

What would that even look like? What would you do to increase the safe speed of road? You'd widen the lanes, limit access etc... All of these things are antithetical to making a road safer for non-motorists.

> Traffic calming isn't decreasing the safety of a road, it's decreasing the perceived safety of driving at higher speeds.

It is decreasing the actual safety of driving at higher speeds. And at lower speeds for that matter. The hope is that people will overcompensate for the danger, so that the safety improvement from driving at lower speed is more than the safety loss from the inherently dangerous design. That is obviously not a desirable trade-off, even when that actually happens.

> What would that even look like? What would you do to increase the safe speed of road? You'd widen the lanes, limit access etc... All of these things are antithetical to making a road safer for non-motorists.

You separate the motorists from the non-motorists. Put sidewalks and bike lanes on the opposite side of each building from the road, so that a building has motorist access on the north and east and non-motorist access on the south and west. Then the building to the north has motorist access on the south and pedestrian access on the north etc.

Build pedestrian tunnels or bridges at busy intersections so that pedestrians and cyclists are never in the road at all.

Houston has a system of underground pedestrian tunnels: https://en.wikipedia.org/wiki/Houston_tunnel_system

None of those pedestrians has ever been hit by a car at any speed.

There are tricks to making roads feel smaller / trickier / slower. Search for the phrase "traffic calming" to find material on the subject.

There is a layer of perception here. People drive faster when they see lots of open space. For example, adding some barriers that obstruct sight but aren't horrible to crash into makes people drive slower without making the road much more dangerous to drive on.

Adding some trees and shrubbery between the road and the sidewalk also does a lot. Because sidewalks next to a road visually widen the road. This has the added benefit of making pedestrians feel a lot safer. No-one likes walking 2 meters next to cars driving at near-highway speeds.

>For example, adding some barriers that obstruct sight

This sounds like a recipe to increase accidents, just saying.

Experience shows they're just the opposite.

The point is not to have much of the environment hidden from sight. The point is to prevent the 'All I see is open road' feeling. On a slightly too simple note, the point is to make you feel like you need to be more careful without actually adding a lot of risk.

One might say the current road design makes roads feel so safe that the actual safety benefits get canceled out by changed behaviour.

Yes. This is a reason why a lot of one way streets are being made into 2 way streets. And why closing streets temporarily increases traffic but decreases fatalities (and eventually decreases traffic)

There is evieence that removing safety devices reduces speeds. Drivers compensate to the conditions. I found this article interesting: https://www.theguardian.com/commentisfree/2016/feb/04/remova...

Case in point: the traffic lights at the bottom of Ludgate Hill were out this morning so cars and bicyles had to negotiate the intersection without any form of communication or signalling. Nobody died.

Traffic lights are not there for safety, they are there to make cars go faster, while being dangerous for pedestrians and cyclists. People are often killed by cars turning right at traffic lights.

Well, here in Sweden the 30km/h roads are often enforced by speed bumps if the cars wouldn't slow down enough by themselves.

Here in the USA, we have speed bumps too. This is why we need to buy huge SUVs with high clearance. With a big enough vehicle, the speed bumps are not an issue. You should try it.

I often wonder what the environmental cost of speed bumps is. It is normal to drive huge SUVs. It is normal to slam on the brakes, go over the speed bump, and then hit the gas. There is also an environmental cost for broken parts that need to be replaced and oil that leaks from broken oil pans.

I bet if you combined speed bumps with a decent gas tax (with tax discounts for business use) and eliminated the "light truck" tax loophole for SUVs [1], you'd probably wipe out the huge SUV syndrome.

Of course, SUVs are highly profitable for the auto and petroleum industries, heavily represented in lobbyist circles, so it's pretty much a no-go.

[1] https://turbotax.intuit.com/tax-tools/tax-tips/Small-Busines...

> gas tax

"How to not get re-elected in the USA 101"

Combining two things Americans hate very much, gas prices and taxes.

While I generally think speed bumps are a good thing your comment made me think.

Also I like the matter-of-factly / deadpan style.

It's a solution, obviously, because people will drive the speed you want them to, 25mph, on it!

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