2003 Urban Mobility Report: 5 Congestion Reduction Strategies
In its annual congestion conditions report for 75 U.S. urban areas, TTI found that freeway entrance ramp metering reduced aggregate congestion delay that would otherwise occur by about 3.8%. Traffic signal coordination reduces total hours of delay about 1.4%; freeway traffic incident management programs results in about 5.0% less delay. HOV lanes are relatively ineffective at reducing congestion, only 0.5%. In contrast, TTI estimates that the presence of public transportation in the 75 largest urban areas reduces aggegrate annual hours of delay by a whopping 29.9%.This information is taken from the document on the TTI website : "2003 Urban Mobility Report: Five Congestion Reduction Strategies and Their Effects on Mobility". (A more detailed summary of this information was recently posted on www.publictransit.us).
Thanks to Michael D. Setty