The 40 Mile Loop was an innovative idea to connect parks and wild spaces around the Portland metropolitan area with a series of boulevards and nature trails, allowing someone to theoretically make a 40 mile loop around Portland without having to leave nature.
While Portland in the last 20 years has been full of enough people spouting out ideas of livability and the like, what is innovative about the idea is that it was actually proposed in 1904, by the Olmstead Brothers, a Boston based planning company. 80 years after they proposed their idea, a company was established to actually buy and develop land for the loop, and now, a hundred years later, most of the loop is done. However, Portland is now much larger, and the loop is now well over 140 miles long.
The basic structure of the loop follows three rivers and a stream: the Willamette River on the west, the Columbia River (as well as its slough) on the north, the Sandy River on the east, and Johnson Creek to the south. It also includes the I-205 Bike Trail in the middle, as well as other shorter spurs and loops.
When the loop is completed, it will be possible to bicycle (or walk, for the truly determined) from Forest Park to Powell Butte hardly having to deal with cars. Most of Portland's best parks, both cultivated and close to wild will be connected. There are some weak links in the system, still, including the Sellwood Bridge, which bicyclists must dismount on and walk across.
Most of the individual parts of the system are complete, including most noticably the Leaf Erickson and Wildwood Trails, which connect the westside from the North End of Forest Park to Council Crest, and the Spring Water Corridor, a trail following an abandoned rail route from Milwaukie all the way to Boring. The only remaining task is to link these trails across high traffic areas, something that will eventually be accomplished considering the deep pockets and influence of the organization that oversees the loop.