Some tidbits I learned about Vietnam. That highway is part of the main highway (the only one) built by the French colonist. It is a single carriage way that pretty much runs across the country. To us, it's a narrow road with only one lane per direction travel. To the people that lives there, it's a full blown four lanes with areas to pass.

See how they drive is on the center line. Drivers have told me they won't get anywhere if they stuck with the lanes of the road, the bikes will start to overwhelm the car. They have to straddle the median to get away from the bikes and to be able to see further down the road. So on that road you will have bicycles on the most outer sides, then motorbikes, then a truck, then you have the overtaken van/busses.

Somehow, they make it work most of the time. But the amount of times I sat shotgun in one of those vans and stare down an oncoming 18 wheeler to have the driver narrowingly cuts back to the right lane in an overtaking maneuver is too many to be comfortable with

Source: am Vietnamese, dad has a family friend in the country who drives on that crazy road for the past 20 years.