I live in the Netherlands, where a few years ago a new class of road was introduced. Secondary roads outside urban areas were divided in two classes:
- the existing class, speed limit 80 km/h with a line down the middle, will now be reserved for roads with no houses on either side, and no bike traffic.
- some roads (with houses) were converted to the new class, with a speed limit of 60 km/h and no line down the middle, but lines at the edge making the road appear smaller than it really is.
In the Netherlands, this works reasonably well.
In the UK, something similar has been done in some areas, but:
- the posted speed limit often isn't lowered
- the road is narrower to begin with
- the edge of the road is full of potholes
The central line was helpful in keeping your vehicle close enough to the center of the road to avoid the worst potholes, without running the risk of colliding with oncoming traffic.
Without it, in wider vehicles you end up micromanaging your position on the road. In a van, I spend more time making sure my side mirror won't get smashed than I am monitoring the traffic situation. My situational awareness drops when there's no central line, and I have to slow down.
Cars don't have this problem as much, so the speed difference between classes of traffic (and the annoyance level at having slower traffic in front of you) rises.