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Comment by thomasahle | Hacker News Reader

"Building 1,500 kilometres (900 miles) of "2+1" roads—where each lane of traffic takes turns to use a middle lane for overtaking—is reckoned to have saved around 145 lives over the first decade of Vision Zero."

I'm no expert in roads, but can anyone explain how that shared middle lane is not the recipe for disaster?

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The 2 or 1 lanes are separated by a metal fence. You can only overtake at the stretches of road where your direction have 2 lanes on one side of the fence.

They did feel a bit terrifying and constrained when we first got them. But now we're used to it.

I did nearly have an accident once when I tried to overtake a truck too close to the road switching from 1+2 to 2+1. Though that was due to me being really really stupid.

It's not an open shared middle lane. There's a wire fence separating traffic. Here's how it looks: http://www.motor-life.com/sites/default/files/articles/vagve...

Meh, in Australia we have plenty of these 2+1 roads with no fence, just road markers. We don't have an epidemic of head-on collisions. All you need to do is at the end of the '+1' section, have the outside lane merge into to inside lane. There's no 'sudden switchover' where traffic in the middle lane is coming at traffic going the other way.

As far I know, the wire fences primary purpose is to prevent cars from going into the opposite lane during a car crash.

Most roads just use a painted dashed line in the middle to indicate that you are on a 2+1, and a continuous white line if you are on the 1+2 side.

Sometimes dysfunctional state politics plays a major role in US highway fatalities. E.g. I-5 [1] in Oregon. It has had numerous head-on crashes over the years because there are no barriers on large stretches of the road.

This isn't a "farm to market" road which some local hicks use to bring their vegetables in to the city to sell. This is the primary Interstate highway that goes North-South from the state of Washington thru the state of Oregon to the state of California. It's heavily used by both local commuters and long distance travelers.

BTW it rains a lot in Oregon!

[1] http://www.oregonlive.com/commuting/index.ssf/2014/11/odot_s...

It's not shared I believe. It's like 1km where northbound traffic has two lanes, and then 1 km where it has just one lane and southbound has 2 lanes.

Not Sweden, but you can see an example here: https://www.google.pl/maps/place/Zyrard%C3%B3w/@52.0700711,2...

Ah that makes sense. I have seen those roads before.

However I've also heard that in crowded situations it's actually faster for everyone to have just two separated lanes (no overtaking). Because the constant lane merging slows everybody down.

Quoting from the "2+1 road" Wikipedia entry:

"It turned out that not only did safety improve, but it was also easier to overtake than before as the 2-lane sections provide safe overtaking opportunities."

"After some good experiences with test roads the system has been used often in places where the amount of traffic does not justify construction of a dual carriageway expressway but remote rural areas should be connected to major towns with a high speed road."

My experience with this type of road in america is that slow people go slow when they have one lane and then they speed up when their direction has two lanes, making it harder to overtake them in the designated section. This is infuriating, of course. In America drivers aware not trained in throttle control, speed control, or lane discipline so their behavior in these situations is usually a combination of the worst possibilities.

That's so incredibly true! But, I'd rather have the passing lane appear periodically than not.

One of my favorite roads in Washington State is Highway 2. On this road, we have the periodic passing lane, at least when we're going Eastbound, we do. Westbound has fewer of those passing lanes; though, I think the lane in the Eastbound side is dashed, so you can actually pass using it if there's not much traffic going Eastbound. Nevertheless, when stuck behind someone who is clearly not following the "more than 5 people behind you: pull over" rule, I long desperately for the passing lane to come, as it appears all the time for the Eastbounders.

I have seen exactly the problem you're describing on /several/ occasions; but, I wouldn't give up the double-lane road, because sometimes people do stay their previous speed and you /can/ pass them. This road is a mountain pass, and so there are several curvy sections, all of which are too dangerous to pass in because you can't see far enough to confirm no cars are coming. When the road grows to 2 + 1 again, you'll see several people enthusiastically pass the slow person and from their slower speeds.

tl;dr: live in the US, love the 2+1 lane when it's around.

Wikipedia did not mention a big drawback with these roads, though: If there is an accident, a vehicle breaks down, or a truck gets stuck in snow (this is Sweden, after all), there is no way for emergency personnel to get to the scene except by going the opposite way. And there is absolutely no way for traffic to get around an obstacle until the center cables are removed.

The "1" part of the road is always wide enough to just barely fit 2 vehicles so an ambulance can always pass a broken down vehicle.

Well, in this case the slow vehicles are mostly trucks, which have a lower speed limit. So if you didn't provide a way of overtaking, a single truck would drop the speed for everyone from 120km/h to 80km/h or whatever the speed limits are now.

There is a railing between the different parts of the road, so no risk of hitting the traffic going in the opposite direction.

Wikipedia picture as reference: http://en.wikipedia.org/wiki/File:MMLNorr1.JPG

Apparently, 2+1 roads are often separated with a barrier in Sweden. That said, while counter-intuitive, it probably just works anyways. I have the following reasons in mind:

- driver attention is higher - road signs tell drivers when overtaking will be possible - overtaking is possible without occupying the other side of the road - distance and speed judgment not needed (and thus not impaired by lack of sleep or alcohol)

A bit of googling would have helped, but the wording in the article is admittedly misleading. The third lane is not shared, but owned by one of the two directions, taking turns. http://en.m.wikipedia.org/wiki/2%2B1_road

In the UK we have sections of road that are 3 lanes with the middle lane shared for overtaking as needed.

Example: http://goo.gl/maps/KI48d

One direction (eastbound in this example) has priority as dictated by road markings, and those traveling westbound can use the lane for passing if and only if it is safe to do so. The onus is on them to ensure a safe maneuver.

With a fairly high standard for the driving test in the UK this is totally normal and as far as I'm aware has a similar low rate of accidents to normal 2 lane traffic.

These exist on many highways in the US. However, if you're behind a slow driver waiting for the passing lane to open up, it's normal for the slow driver to gun it when the passing lane appears and race you to the end of it, then resume driving 15 mph below the speed limit.

There must be some sort of psychology that kicks in when somebody tries to pass you, that more or less forces you to speed up. It's like, "oh, I didn't realize I was going slow until I saw you try to pass me...let me speed up a tad." This seems to happen in any passing situation, whether on a two lane road with a passing lane or an eight lane highway.

I drove on a highway like this (in America) this weekend. It's not really shared. It's just that your side will get two lanes for a while, then merge down to one. Then the other side gets two lanes for a while. There are frequently signs saying how far until the next two-lane section, which presumably pacifies impatient drivers.

The middle lane is not shared, it will only be used by one direction at a time and a middle barrier is usually separating these two. Wikipedia has an article explaining it further: http://en.wikipedia.org/wiki/2%2B1_road

It's not shared. It replaces single lane roads where you overtake into oncoming traffic. Driving is one of those things that lots of people thing they are better than average at.

This removes drivers having to judge when it is safe to overtake, you just have to sit back and wait for the middle lane to switch back.

They usually have a barrier between them. So it's not really shared. Wikipedia has some pictures and videos, conveniently enough they were taken in Sweden.

In the past, in France this recipe was default in country roads, they changed it a long time ago to alternating lanes, there's no divider though..

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