I tried a sidewalk bike rack once. Can't remember why it didn't work out. Changed over to a 2-bike car rear rack in the center of the trailer which was much faster getting the bikes on and off. I could easily carry 4 at a time without stacking any on top. I'll see if I can dig up a photo of the final answer to hauling multiple bikes from a bike shop to our warehouse without having to mess around with trucks and parking spots.
The bottom photo is one bike in the middle and two lashed to it.
Bikes At Work trailer.
Bikes At Work trailer.