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Comment by landemva | Hacker News Reader

Much idling could be avoided if traffic engineers would design roundabouts instead of 4-way stops. Nevertheless, some newer cars shut off at intersections and are designed for that.

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Roundabouts have a failure mode that 4-way stops don't, akin to starvation in computer science. Consider a roundabout in a right-hand traffic country with connections in the 4 cardinal directions. If at a given time of day, there's a constant stream of cars from the west that want to go east, and virtually no traffic from the north or east, then a car trying to enter the roundabout from the south will be waiting a very long time.

In practice this rarely happens though.

It’s very common in major French cities. The workaround is to stick a traffic light on the input lane that gets too busy

Yes, same here about 300 meters from my house. I've seen it operational maybe twice or so.

> Roundabouts have a failure mode that 4-way stops don't, akin to starvation in computer science.

Putting roundabouts onto streets is not a binary decision: some intersections could be roundabouts, some could be lights, and others could be roundabouts with lights.

If there's that much traffic, a four way stop will be even worse than a roundabout. You'll need a turbo roundabout, traffic lights or grade separated intersections in that case.

Four way stops are one of the dumbest inventions of man kind that are way over used in North America. Everyone has to stop all the time and it leads to scary situations at 2 way stops because people don't expect those anymore.

Here is a great video about life without stop signs in the Netherlands: https://youtu.be/42oQN7fy_eM

And here are some infinitely better alternatives:

Low traffic + low speed: raised intersections where right goes first.

Medium traffic + medium speed: priority road with yield signs on side streets and roundabouts

High traffic + medium speed: traffic lights

High traffic + high speed: grade separated intersections

> a four way stop will be even worse than a roundabout.

Maybe for people coming from the west, but it'd undeniably be way way better for people coming from the south.

Large UK roundabouts often have traffic lights that are only operational at peak times, to counter the effect you describe.

Small roundabouts don't have this problem.

A single “pause” (traffic light, roundabout, stop sign, even just a speed camera or change in speed limit…) in the stretch of the east-west road leading up to the roundabout can usually solve this. You only need occasional breaks in traffic to allow the secondary traffic to join.

There was such a roundabout constructed by my prior job just outside the 4k factory parkinglot entrance.

Almost everyone were going from the highway to the parking except me.

I had to wait for a bus that was going straight so you could enter or two cars going straight in a row.

It got so bad that the workers started to give way to those coming from the starved road so it sorted itself out I guess.

A lot of walking would be eliminated too if you actually completely got rid of perpendicular intersections. You kind of need cars to stop sometimes to make it possible for people not in vehicles to get through safely.

There are still crosswalks which are distributed around the circle. Rarely there are pedestrian tunnels to get inside the doughnut, like in Paris to visit the arch.

In Arnhem they did the reverse: Vehicular traffic is raised to a higher level and pedestrians and bikes take the lower (inner) level.

https://www.google.com/maps/place/Airborneplein,+6828+KP+Arn...

It's extremely efficient.

That's really awesome, but you need a tremendous amount of land to make that possible.

Most roundabouts of that type I know have replaced similarly sized all asphalt intersections. Now there is more green. When planned ahead there really isn’t that much extra real estate required if you are willing to have steeper grades for pedestrians only for example.

Oh wow, years ago I randomly came across that place upon once when I was in Arnhem and was very confused about it, interesting to see it here!

I definitely like the idea of this but it seems like the tendency is always the opposite because it's much cheaper to build a pedestrian overpass than a car one, even though they're also an accessibility nightmare and usually kind of a terrible experience and aesthetic blight in their own right.

Those crosswalks tend to be -in my experience - some of the most stressful to interact with. If they're controlled then you've just made the whole thing even worse than they were before. If they're not then you've got a much harder time as a pedestrian to figure out when it's safe to cross (because of the curve) and the traffic all wants to free flow.

I dunno. Maybe I just haven't experienced the right ones, but my experience is that the most pedestrian friendly urban spaces have mostly (roughly) straight lines and right angles and lots of natural or man made barriers to free flow of cars to prevent them from going too fast. I don't know how you can square that circle.

One option:

* https://en.wikipedia.org/wiki/Pedestrian_scramble

Oh wow never knew this had a name and have been curious on the origins/history of the "diagonal crosswalks" for a long time - have only seem them in specific districts/neighborhoods in Oakland/SF.

Thanks for the link, a bit sad to read to following(!)

> later fell out of favor with traffic engineers there, as it was seen as prioritizing flow of pedestrians over flow of car traffic.

Mathematically speaking I am not sure why they are not all like this. It means one pedestrian phase in the sequence (so sequence is quicker) and everyone is a winner. There is one near me it is a joy to go diagonal!

It's only better if the intersection has high, consistent pedestrian traffic. Unfortunately, many cities aren't built to be pedestrian friendly so those criteria are rarely met outside of busy cities, downtowns, and college towns.

But if the intersection allows pedestrians at all it needs two sets of allowing pedestrians across.

Unless it does that awful hybrid “turn if no one is crossing” crap that I hate as both a driver and pedestrian.

It's not the idle at the stop sign that matters, it's the slowing and and re-accelerating afterward. Idle itself uses a trivial amount of gas - equivalent to around a tenth of a mile for a 15 second idle.

10th of a mile at 15 seconds is the equivalent of doing 25 mph. I'd not call that trivial considering you're not doing 25mph.

Then my math must be off. 60 miles/hour at 15 miles/gallon = 4 gallons/hour.

Idle is like 0.15 gallons/hour. There's no way 25 mph uses that little gas, if 60mph uses 26 times as much.

> 60 miles/hour at 15 miles/gallon = 4 gallons/hour

What 1960s car are you driving? :) Should be getting 50-80mpg at 60mph.

Have you ever tried to navigate a busy roundabout? I've been at roundabouts backed up at least a quarter mile. There is plenty of idling.

The cost of managing cars is so huge, we should really have more fluid intersections.

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