So this is not my idea. Its been around for awhile. Its actually kind of two but they could be combined. One is to have a one way bike expressway where going out of the city starts high up in the city and its end destination is at ground level and the reverse for going into the city. Every so often there are egress/entrance points with stairs. The idea is that you are riding very slightly downhill. A similar thing is covered bikeways that are one way and completely covered tunnels that have negative pressure so the wind is always at your back. That could have interchanges to switch direction. Also the concept could be combined so your ride into the city is covered, downhill, and with the wind at your back. I can say this. Where I was at biking into the city seemed to be overall slightly downhill and in the morning the wind seemed to mostly be at my back and in the afternoon coming back it was reverse (slightly uphill and wind in face) combine that in the summer with the mornings being cooler and oh man biking in was way easier. I used to bike in and then bring my bike on the train for the way back (which by the way was awesome.)