Why do some roads have two lanes that suddenly merge into one?

[Kingofkings1992]

I can’t for the life of me understand why anyone would design something like this. It’s just so incredibly dangerous and increases the risk of an accident happening

[purplepoppy]

Usually it's a single road that temporarily turns into two lanes to let you overtake slow vehicles. Often they are on up hill stretches. The game is to try and overtake before it turns back into one lane or you'll find yourself trapped in a dangerous situation. I've seen quite a few near misses.

[MuddyMole]

Do they really "suddenly merge into one"? There's a big sign to warn you - probably several, in fact. And then there are probably also arrows painted on the road, telling you to move across. And then there's probably even a lengthy section of road with hash markings after the point where you're supposed to have merged already, just in case you really can't get over in time, for some reason (like if the car you're overtaking decides to accelerate).

[RavVid]

It allows overtaking on country roads without getting onto the opposite side to do it.

[supercutebutt]

The sign should show two lanes becoming one, not two lanes getting closer to each other. The sign designer needs to be fired.

[Kelley1]

There is adequate warning. Moreover, when traffic is less, fewer lanes are required.

[exitseven]

The state ran out of money and could only afford to make one lane.

[noohair]

This is urban planning by civil engineers. They study traffic flow and make decisions based on an educated guess on population growth.

[Twalli]

Less traffic means fewer lanes. Drive through the US enough and you'll be on 2 lane highways.

[DrPepper12]

It's cheaper. Simple.

[Kingofkings1992]

Why wouldn’t it just be one lane the whole way through?

[DrPepper12]

Minimum safety standards, grading, elevation, drainage, etc