Excerpt:

Development both on and off the Island will create a lot of traffic on Alameda’s major roads and in the Webster and Posey tubes, the city’s planners and studies done for local development proposals say – impacts that some fear will overwhelm the Island’s arterials, creating commute hour carmageddon. But quantifying those impacts – effectively, predicting the future – is a more elusive matter than the studies let on.

Almost every time a developer proposes a new housing project on the Island, the city conducts a study to figure out how many more cars will traverse Alameda’s roads, tubes and bridges each day using live traffic counts and a computer model that takes both local and regional job and housing development projections into account. Using the model, the city calculates traffic impacts to major intersections and crossings down to the number of seconds of delay drivers experience, typically at peak morning and evening commute hours.

But those traffic numbers can range widely from study to study – even when the same intersections are being studied. Both the local and the regional job and housing development pictures are constantly changing (the economy is another factor driving traffic). Even the capacity of the city’s roads and crossings can change, based on the presence and timing of traffic signals. And no one really knows what people’s commuting habits will be decades from now.