If a bridge is modernized, you might assume that more people will be able to cross that bridge. But the reality seems to depend on what means is used to move the people across the bridge.
StreetsBlog did some digging when they ran an old photo of the Brooklyn Bridge (H/T John Petro and The Overhead Wire). They found that the bridges into Manhattan are now carrying just a little more than half of the number of people they did in their peak years (which ranged from 1907 to 1940). The major difference? The bridges were shifted from multi-use (private vehicles, transit lines and pedestrians) to single-use (private vehicles).
This suggests that the modernization of bridges isn’t necessarily connected to increasing the volume of traffic flow. Now I am not suggesting any kind of Robert Moses style plan to keep the poor out of Manhattan by cutting off transit and pedestrian access to the city. After all, there are plenty of people walking around Manhattan, and transit into the city isn’t limited to the surface. I think it does suggest that transportation improvements are not necessarily connected to preferences like efficiency or capacity that can be easily quantified. Much in the same way that policy options that seem dictated by the science aren’t always chosen, policy choices involving technology aren’t necessarily made on the basis of what relevant engineering suggests.
And please don’t disregard something because it’s old technology.