The source data is freely available for download in CSV format from the New York City Taxi and Limousine Commission (NYC TLC):
The downloadable yellow cab source data consists of 77 CSV files – one per month, starting in January 2009 and terminating in June 2015 (note that the December 2011 data is not available). The data files are named yellow_tripdata_YYYY-MM.csv; each file is approximately 2GB in size. The data dictionary describing the format of the CSV files is also available for download on the same page.
The following graphic shows the 2014 yellow and green cab data download links from the NYC TLC site: