Depends on the speed limit.

Around here, on larger streets the speed limit is 35 mph. Riding a bike is considered a rather dangerous activity.

Drop the speed limit to 20 mph and maybe sharing the road becomes possible.

Seeing how other countries do it though, true separated bike lanes are the best. I agree that studies show painted bike lanes are actually more dangerous, but a physical barrier between cars and bikes is going to be the safest solution.