Cars in the 1970's were big, slow to get up to speed, slow to stop, and handled like they were riding on marshmallows. And the United States had a 55MPH speed limit across the country. Cars got better, much better, and the speed limits have gone up accordingly. Horrific looking accidents are far more survivable now because of massively improved safety standards. In many regions, time spent in traffic is improved because people are free to drive up to 75MPH on many interstates while staying in sync with the flow of traffic. Getting people moving faster allows the highways to allow more vehicles to travel on them per day. We should be figuring out how to safely get the speed limits up, not down.
I don't know about other countries, but in the US the redaction of the white line will give a license for a whole new level of passive-aggressive driving (as well as more overtly aggressive). We already have problems now with people who hog the fast lane, or who speed up and slow down to prevent other motorists from overtaking them or otherwise joining their lane. I can see that same class of jerk swerving back and forth to hog more of the road for themselves.
Sounds like a great recipe for increased accidents, road rage, and congestion. No, thanks.