This February 2008 study was prepared by ICF International in conjunction with Dr. Pat Mokhtarian for the American Public Transportation Association (APTA), with funding from the Transit Cooperative Research Program (TCRP). Based on data from the National Household Travel Survey 2001, the study found a significant correlation between public transit availability and reduced automobile travel, independent of travel use. This secondary effect results in lower total vehicle miles traveled (VMT) even when people are not substituting automobile use with transit use. The presence of public transportation results in more efficient land use patterns in community development. This allows areas to support more travel with fewer roadways in less space and saves 4.2 billion gallons of gasoline, reduces CO2 emissions, and lowers overall energy consumption. A 2007 ICF study assessed the total number of VMT required to replace transit trips and the direct petroleum savings attributable to public transportation.