For the past 50 years, roads have been widened from two to four lanes when the number of cars on that road (average daily traffic, or ADT) reached approximately 12,000 per day. New research shows that well-designed two lane roads can carry up to 30,000 cars per day. There is the possibility that we have unnecessarily widened thousands of roads.
Several ripple affects occur when a road is widened from two to four lanes. Houses are usually torn down to make way for more asphalt, which can cause more driving. Another affect is that people who walk or bike may drive more because of the increased danger of faster traffic and wider roads to cross. More traffic increases noise, pollution, and stress. People move out of the city to escape these problems, leading to yet more driving. This process is one root cause of sprawl.
To reverse this trend we can reverse the process that leads to unnecessary driving in the first place- reducing 4-lane roads back down to 2-lanes where traffic volumes are less than 30,000 vehicles a day. We highly recommend the article 'Road Diets', put out by Walkable Communities (see below).
By reducing the number of lanes on a roadway, there would be room to put in bike lanes or cycle tracks, landscaped boulevards, medians, street trees, wider sidewalks, etc. A road diet combined with roundabouts and cycle facilities could turn a town around.
on the Broadway Road Diet
a letter from a local engineer on why Broadway Avenue can be 'dieted'
an insight on the flaws of the engineering term 'Level of Service'