I've been stewing on an idea for an elevated and covered set of bikeways for cities large and small. They would also effectively cover roadways where they are installed, vastly reducing the need for Winter salting and plowing. (So you would give street repair & plow crews first crack at building and maintaining them.)

Imagine a city-wide network of elevated bikeways that had roofs but open sides and were elevated above major streets. They would be made out of clear recycled plastic. Basically, they would have three levels, motor traffic street level, then bikeway, then roof.

The system would be entirely modular in design, with built-in plumbing, electrical, communications, and solar power panels for lighting at night, planters for greenery, etc. There would also be built-in bike elevators and ramps.

Sides could include spaces for small bike repair kiosks, tea & coffee shops, sandwich shops, convenience stores, etc.

This would allow bicycle, moped, and pedestrian traffic to be out of motor vehicle traffic and shielded from precipitation.

As the modular system started covering major thoroughfares in a given city, bicycle and moped commuting would become much easier over longer distances. Cities that were early-adopters would wind up as cycle-tourism destinations in a big way.

This goes way beyond Portland or Copenhagen, but it would also compliment existing street & ground-level cycle trails.