[jakecopp]

> there are probably enough to build a pedestrian layer _above_ the car layer entirely. Isolating large vehicles from fragile human beings is the best engineering

As far as I can tell, the general consensus among urban planners is that building pedestrian overpasses/Skyways/skywalks is a _really bad idea_.

They suck pedestrian life away from the ground plane and surrender it to cars, which has all sorts of second order effects.

The ground level becomes darker, and more dangerous with less "eyes on the street". Car focused transport planners are more bold to increase traffic volume (with increases in pollution/crashes/noise). Businesses on the street struggle.

> Isolating large vehicles from fragile human beings is the best engineering solution.

It may be the best _engineering_ solution (don't get me wrong, I love some Brutalism and textured concrete), but it's usually a horrible outcome for street life. The best solution for a healthy, livable street is to build large spaces for pedestrians and cyclists, reduce car speeds to 30kph/20mph, or remove cars altogether.

[throwaway2037]

Hongkong has a lot of raised pedestrian infra in the central business district. It is difficult for people with "reduced mobility" (disabled, old, baby cars, etc.) to navigate. As a second order effect, it has turned street level into somewhat of a Mad Max zone where cars drive as fast as possible knowing there are no pedestrians to worry about.

Related: Hongkong also uses (awful) metal gates to keep pedestrians caged into sidewalks. Again: It makes drivers more aggressive. When I visited Shanghai, a lot of sidewalks blended into the street which had an interesting effect: Drivers were much more cautious because people frequently flowed into streets.

Last comment about lower car speeds: I recently drove on Japan (100% grade separated) expressways in Tokyo, Kawasaki, and Yokohama. At first, it seemed so damn slow. Mostly 80 km/h, but many places slowed to 60 km/h. Really, 60 km/h feels like crawling on an expressway! Always two lanes each direction. Very few on/off ramps. However, after driving more than an hour, I could see the effect: Traffic flowed very smoothly, even in very busy areas. I can only guess this is intentional design.

[Symbiote]

England, especially London, has removed a lot of those railings in the last decade, for exactly this reason.

(I was amazed just how similar the street level design of Hong Kong was to London when I visited. Of course, it had a century of being constructed to the same standards and regulations.)

[kelnos]

The Las Vegas Strip makes heavy use of pedestrian overpasses, but I don't find them to have the negatives you describe. Possibly because the area is so lit up (even at night), cars are kept deliberately very separate from from pedestrians (a lot of drunk people roaming around), and in many places the above-ground overpasses connect to the second levels of adjacent buildings, which makes them a more natural part of the cityscape.

I'm not sure that kind of design can work everywhere, but it can perhaps be an option in some places.

[mjevans]

Not a ped overpass, you've misunderstood.

Literally raise the 'pedestrian ground level'. I've also realized that construction cranes and other things that need to poke up through that level should do so by rotating and shipping away the cap segments that the pedestrians walk on and blocking off a work site while in use. Though they'd do that anyway for safety.

[roxgib]

Yeah, overpasses are definitely the right choice in some places, but I'd quickly grow tired of them if I had to cross a few in a row. The USYD overpass on City Rd is a good example - a lot of people opt to use the street crossing rather than the overpass, and it's pretty easy to access compared to some (e.g. nice long ramp instead of stairs)