So I was trying to exploit the additional set of paths used by public transport stations, to make custom pedestrian bridges. The result is astonishing: people will follow the geometry hinted by the walking paths. Some insights:

1. The Pedestrian Connection Inside ("Inside paths") from the train stations is one of the path types that pedestrians can use. The problem with it, however, is that it will teleport people, or hide people when they are moving.

2. Another path called Pedestrian Connection "Surface" ("Metro paths"), will not hide people when they are moving. It is therefore the best option to hint a path for pedestrians. Metro stations also include a third type called [ditto] Underground, but I haven't tested that out because I have not found a way to substitute it in a new asset. Its name is of unique length, 33 characters long, so it can't be substituted for any other path.

3. People walking on sidewalks will often jump onto the bridge if we put the hinting path's two ends directly above, or within a certain distance from the sidewalks. So we can't do the hinting path by making separate "approach - bridge - approach" segments. They will ignore the approaches and jump right onto the bridge section. Instead, I have forced my people to use the approach sections by ending the on-segment right on the road-center line. The path then consists of only two segments, one on each side.

4. The ideal case, had Cims not chosen the shortcut onto the bridge, is that we can hint the path 100% accurate following the model geometry. But even then, we are still limited by the minimal length required for a segment to be placed in game. I am not sure on this number, but one thing I can tell is that it takes into account the curve-control point too. I can create a really long segment, still getting "Distance Too Short" errors, by moving one end to the proximity of the curve-control point. The game also throws "Invalid Shape" errors when the turning angle is too sharp.

5. Lastly, the crowd likes to spread out when it moves. The channel must not be too narrow for the crowd. The original model (http://i.imgur.com/q3vtrKF.jpg), 1.8 meters wide, has often seen people walking on an imaginary floor. I've widened the channel to 3 meters, and it works just fine for my cims. I think it might be a magic number, no?