An exhaustive transit study by researchers Gilles Duranton and Matthew A. Turner from the University of Toronto found that building new urban highways simply increases traffic volumes and building public transit (such at the Red Line) has virtually no effect on traffic volumes. The study found that if drivers switch from cars to buses or trains, it has much the same effect as adding new road space: traffic clears up temporarily, but faster travel quickly attracts more drivers who take longer trips. In short, congestion reductions are short lived at best. The Sightline Institute describes the study as well thought out, rigorous, employs careful controls to separate cause from effect, and uses the best available data for the US transportation system from (I kid you not) 1835 to the present. Click the below link for access to the article and full study.