We often use a MUP to get back into town. I consider it like a highway for bicycles. Sometimes it is busy and you need to drive slow and sometimes, you can just fly--all depends upon the day.
However, I'll take periodically slowing way down and maybe having to help coach a 6 year old on riding to the right over having to negotiate cranky cars. The MUP in question covers 1/2 the width of the state and is straight (old railroad bed). 99% of the people on the trail, be they runners, walkers, cyclists, skaters or dogs, are cooperative so rush hour on the MUP is rarely an issue as long as you're not trying to go 25mph.