New York's Broadway almost got an elevated moving sidewalk in 1872
Really, New York's High Line is so boring, it just sits there and you have to do all the work walking on it. And who needs Elon Musk and his Hyperloop; New York could have had its own giant moving sidewalk loopy high line running up and down Broadway. That's what inventor Alfred Speer patented in 1871 and proposed in 1872. Dana Schulz of 6 square feet describes it as...
...an aerial, steam-powered sidewalk (much cleaner than the locomotive trains) that would make a loop up and down Broadway to alleviate traffic. It would be constantly in motion at 10 miles per hour, carrying passengers by foot or in its movable chairs for five cents a ride.
Newspaper illustration of moving sidewalk/Public Domain
The sidewalk was cable-driven, propelled by remote steam engines so that the soot and smoke could be dealt with away from all the customers- very environmentally friendly compared to an elevated railway. It was to be built 12 feet away from buildings, giving store owners an option of having a bridge across to it; there were also supposed to be what Dana calls "very High Line-esque" stair access points at street corners. Along with the moving sidewalk and moving seats, there were to be heated smoking lounges for men and women.
Corner access looks like the high line/Public Domain
It might have actually got built if not for the New York Governor (they seem to have a long history of interfering with New York City transit plans) who, according to Untapped Cities, " vetoed the plan twice, objecting to the moving sidewalks’ interference with street-level sidewalks, the price tag and its layout." Interestingly, a slightly earlier pneumatic subway was also killed by politics and entrenched interests. Some things never change.
Google Patents/Public Domain
Digging into google patents reveals how the moving sidewalk would work: it was made up of what were essentially flat topped connected platforms on wheels, like very low railway cars. However Speer had the same problem that vexes moving sidewalk designers to this day: How you get people from zero to ten miles an hour without them falling over. So he designed a complex system of transfer cars with handbrakes, figure 3 in the drawing above. You would have to sit on that bench, pull the brakes to separate the transfer car from the sidewalk and slow it down, and then step off onto the fixed part of the walkway.
Any suitable number of these transferring-cars will be arranged along the whole route, so as to be at all times at the service of passengers. Many persons may get on and off at the same time, according to the capacity of the transfer-cars.
Google Patents/Public Domain
There is also the question of how the moving sidewalk would turn corners; that shows up in another patent from 1874 along with the method of propulsion. The end of each platform section was rounded so that the convex end of one car fit into the concave end of the other. There appears to be a plate running down the middle of the car, L, which slides through those M rollers at the bottom of the drawing. It's complicated and probably would slip, although "These rolls may be faced with india-rubber, if preferred, to increase the friction. Springs may also be used to press them on the flange."
I suspect that the Governor saved Alfred Speer from a lot of embarrassment by killing this thing. But it is an idea that never goes away; It was proposed for New York in the 1950s and recently in London for the Circle Line.
ThyssenKrupp has developed a variable speed moving sidewalk called ACCEL that is used now in airports, but they are also proposing it as a way of bridging the gap between transit stations.
Recent research has revealed that if a metro station is just over 500 meters from a home, commuters are more likely to travel by car, even if it means sitting in traffic. Enter ACCEL to bridge the gap. Constructing feeder points between metro stations brings public transportation solutions closer to home.... With more people on ACCEL, and less car traffic, new megacities can keep down CO2 levels, without limiting residents’ freedom of mobility.
Perhaps they will build it on Broadway. Here is a video of an earlier version of it in action: