classicalgas said:
Cargo trikes are useful only where they can take advantage of pedestrian walkways, narrow alleyways for delivery, or some other little niche.
I dunno--I ride almost exclusively on the roads in traffic, max speed of 20MPH, with SB Cruiser (and sometimes a big trailer, when necessary, but usually just the trike itself). Wouldn't work on major roads in high traffic, but I deliberately avoid places that I'd cause problems with faster traffic, wherever possible.
In my experience, walkways are a terrible place to ride, not least because cars/etc cross them frequently and unexpectedly at various driveways (too often without looking at the traffic that's already on the walkways), so one must constantly slow or stop to make sure no one is about to pull out (or in) in front of you, or go no faster than walking speed at best, to ensure no collisions occur.
Another problem is the driveways themselves--a trike will suddenly tilt significantly on every one of those, with the road-side wheel suddenly dropping several inches (whatever the sidewalk height is) vs the other-side wheel that stays at sidewalk height, becuase of the driveway ramps. There are often somewhat long stretches of sidewalk that have no driveway, but rarely more than a few dozen feet in many places I ride. A few hundred feet at best. Not much fun getting seasick from the constant seesawing side to side that way, and if any of your cargo is not tied down well (or you carry live cargo like I do)....
Then there's the problem of other cyclists, and pedestrians, that are on the walkways. Can't expect them to get off the walkway for you, and the trike is likely to take up all (or at least too much of) the walkway, leaving nowhere for anyone else to be when you go thru the area. In the very few places I have to use a sidewalk, I may have to pull over at least halfway, often all the way, onto the lawn or rocks or whatever to the side of the walkway and stop and wait, so that others can get past me and I can then continue on.
Then there's light poles, signs, trees, etc., that sprout from walkways (even ones "designed" as cycleways), that a cargo trike (at least not one wider than at best a narrow-person's shoulders, sometimes not even that) simply can't pass and still stay on the walkway. (some of these problematic things in the middle of walkways block wheelchairs, too. Doesnt' seem to be a priority of any kind to fix the issues, since nearly all of the ones I can think of off the top of my head have been that way since at least the 1980s, except for the ones that have been built wrong since then).
Anyway, I (and others) can use the streets for cargo trikes easily enough, with the caveats that they need to obey the traffic rules, and avoid areas with high-speed-differential-traffic to their speed, and I'd strongly recommend DOT lighting/signals, or the equivalent or better in DIY/etc.