[0] FTA "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"
imagine a road like this: http://lh6.ggpht.com/_gt_enTZIj1g/TMq0zFITxUI/AAAAAAAADo8/Rb...
(not sweden but Netherlands but it works for the example.)
Overtaking is not allowed (except for farm traffic), in a 2+1 situation there would be three lanes all the time, alternating between directions. This means that there will always be a legal spot to overtake within a few minutes. (usually the climbing direction would be two lanes so you can overtake slow trucks e.d.) Therefore you don't have to overtake a slow driver by using the oncoming lane.
By a 'standard 3-lane highway', I assume you mean three lanes each way, these roads have nowhere near enough traffic on them to explain all that extra tarmac.
We have a few of these roads in my area but not very many, and you can easily go many many miles on a road similar to the one in your picture with no passing lane.
The advantage of these is that rather than forcing drivers to overtake into opposing traffic, they can wait until their direction gets the overtaking lane. These sort of roads are very common in Denmark. And I've seen a few of them in Germany as well.
(This is not to be confused with 2+1 highways where the middle lane change direction depending on the time of day, these have been phased out. There are usually clear markings on 2+1 highways when the direction change.)
all the 2+1 roads in Sweden have barriers.