It is great that Portland has such an integrated transportation/environment to media system. It seems like every three weeks there is a huge article on the issues. It is great to see that the concept of induced traffic is alive and well. Although I don't agree with the concept like I used to. I think it is more like a system. Increased road capacity leads to land use patterns that utilize that capacity, i.e. people buy homes that are to their liking (reasonable commute, land for the kids to play, "safer" communities, newer parks, nice schools that leave the poor neighbors behind, lower taxes because they don't pay for the infrastructure like museums/libraries/Convention Center if owned by the City/etc, further from their work because the commute isn't that bad, and then later when it gets bad the community asks for improvements so that they don't have to move.
So at the end, you have travel that increases not because of the additional capacity persay, but rather becuase of the land use that follows the roadway capacity. The challenge is you need a certain amount of capacity to address freight and other important societal needs. I am not sure what the right answer is, I guess it would have to be improve the bridge, but make sure there is high speed transit and auto capacity (properly priced), and of course bicycle facilities.
Anyway, here's the excerpt: In fact, if you build it, however, they will drive…more.
There’s a concept transportation planners call “induced travel,” which means more road capacity results in more traffic.
While the precise relationship between capacity and demand remains under debate, CRC figures show if a new bridge were built without tolls, the number of people crossing the Columbia would increase dramatically, versus the no-build option. Figures show that without tolls, a new bridge would carry 225,000 passengers a day by 2030, while the current bridges, if left in place, would carry only 184,000. The difference of 41,000 is the “induced travel” generated by the newly built capacity.
If, as the task force proposes, the new I-5 bridge is tolled, and an adjacent light-rail, bicycle and pedestrian bridge is built, that combination would reduce traffic by 47,000 car trips, leaving only a small net reduction—6,000 trips from the no-build scenario (see chart below).