=cities =traffic =suggestion
Four-way stops are common, but they seem inefficient. Maybe they can be improved by people just following different rules.
When an intersection with stop signs has too much traffic, the signs are replaced with traffic lights. Why does that allow more cars through? Because many cars go through before the light changes.
But the same principle could be applied without having a traffic light.
Take a 4-way stop intersection, and paint some lines approximately 3 car lengths away from the intersection on each lane approaching the intersection. Have people treat the intersection as a 4-way stop, but have people who stopped on or in front of the new lines go through the intersection at the same time as the person in front of them, unless someone in front of them makes a left turn.
This should allow for better traffic flow than current 4-way stops.
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response to comments
This post was recently linked to by Marginal Revolution, a much more popular blog than this. It's nice to see that my posts here still have some potential value 7 years after being written. Here are some responses to the top related comments there.
George
Templeton Wrong: People aren't obeying the simple rules that exist now.
XVO: People can't handle that complexity.
Dinwar: It adds to the
cognitive load of the driver, which will necessarily reduce safety. A person
in charge of a multi-ton vehicle should NEVER have to wonder "Do I go now,
or am I supposed to wait, or what's happening?"
Zebes: So many people
would screw this up.
In the USA and Europe, various
uncommon intersection types are operating successfully, including
Michigan lefts,
continuous-flow intersections, and
turbo
roundabouts. With this stop sign proposal, what each driver needs to do
differently is: follow the person ahead through the intersection unless they
see a pattern painted on the road in front of them. That's not very
difficult - easier to understand than the linked intersection types.
The main failure mode would be drivers treating the intersection as a normal
4-way stop, which would be the same as the status quo. Another possible
failure mode is more cars following the leader through the intersection than
are supposed to, but that's also not very bad, and people who won't follow
that kind of traffic rule probably won't follow other traffic rules either.
The failure modes have low risks of serious injuries, and road paint is
cheap so the physical implementation isn't expensive. That being the case,
I'm disappointed that there were several responses saying this proposal is
too complicated for drivers to understand, but nobody who pointed out that
it could be tested in a few towns to see how well it works in practice. I
prefer cultures with more empiricism than that.
TMC: Simple way to add capacity is to have both cars across from each other go at the same time when neither is taking a left. A lot more intuitive.
That's already done now, and I thought continuing to do that was implied in my proposal.
David Jay: Why the limitations for left turns?
Cars turning left must first wait for oncoming traffic to pass, which usually requires them to stop in the intersection. If the cars behind a left turner are stopped, then there's no advantage to them going next instead of the cross traffic, which may have accumulated more cars in the meantime. Also, switching traffic direction every time cars stop is easier for drivers to understand.
mkt42: I could see it basically working, but it requires all drivers to have good visibility three cars back in all lanes so they know how many cars are supposed to go through. If there are parked vehicles or bushes, drivers might not be able to see that far.
No, that's not necessary. Drivers
should wait until cross traffic stops entering the intersection before
proceeding anyway. If they don't, they could hit a car that stops to turn
left, or a pedestrian they can't see behind the cross traffic, or a car that
needs to stop quickly to, say, avoid hitting a cat.
The point at
which cross traffic would start to go is clearer if traffic behind the
painted lines (which won't continue through the intersection) waits a few
seconds before proceeding. It would be good for drivers to do that, but at
the time I didn't consider it worth mentioning.
Kaleberg: In Massachusetts, at ordinary stop signs, the second driver doesn't have to come to a full stop at the sign if the first driver did. The result is that drivers just run stop signs.
I don't think that's a correct description of Massachusetts traffic law. This sounds like a case of culture diverging from law.
Kaleberg: Once one car goes through all waiting cars follow. Once drivers get used to going through a stop sign because the guy ahead of them went through the stop sign, the fifth guy isn't going to give a crap that he's fifth, not second. No, those painted lines aren't going to make a difference.
Kaleberg: You have clearly never driven in Massachusetts. The usual strategy is to enter the roundabout at speed and rely on the driver with the de jur right of way to slam on his brakes and let you in. The de facto right of way is momentum, the product of speed and mass, so heavier vehicles and faster vehicles get right of way by right of intimidation.
It can certainly happen that
drivers start applying game theory instead of following the traffic rules,
but there are 2 points I'd like to make about that.
1) Considering
the game theory of a traffic intersection and driving according to the Nash
equilibrium is more intellectually difficult than following the rules as
written, so this is an opposite criticism to drivers being too dumb to
understand the rules.
2) If drivers all act according to the Nash
equilibrium with no traffic law enforcement, then the signs and rules are
ignored and don't matter. That may be the case in some parts of India, but
the US has approximately
1/10 the traffic fatality rate per vehicle-year.
If people are going to make
criticisms of the form "if you change the rules, people will do [X] instead
of following the rules", I think they should be clear about why people don't
do [X] now. Since that wasn't done here, I can only guess at some possible
reasons.
1) There's a psychological barrier to following cars past a
stop sign that's bigger than the psychological barrier to breaking rules
about doing that.
2) The only reason people don't follow cars through
a stop sign is because they're afraid some eager cross traffic will hit
them. More cars following others through intersections causes a phase
transition to an equilibrium with less eager cross traffic.
I think
(1) proves too much: for example, if speed limits are set too low and
drivers speed, that doesn't suddenly make a lot of drivers go faster. Also,
if this is how drivers in an area actually think, then 4-way stops are
probably unsafe and the city needs to have every intersection either be a
roundabout with traffic calming devices or have a traffic light and cameras.
As for (2), as I said above, cross traffic at 4-way stops being that
eager is dangerous and bad, so less of that is good.