To start with, let's look at our own government's current surprisingly alarmist position using the 2007 National Surface Transportation Policy report.
It's worth noting that this is just one of several extremely major relevant and reputable reports to come out recently, including 2007's United Nations (4th) Global Environment Outlook Report which is 572 pages, 1993 U.S DOT report "The Environmental Benefits Of Bicycling And Walking", and the Lung Association ongoing report on auto pollution deaths, not to mention the slew of recent documentary films.

This report (over 260 pages) mentions bikes specifically very little. It is by nature based on the angle of maintaining an automotive highway system, and was produced under an oil friendly administration. But even so, it has reams of well supported interesting things to say about the current state of transportation affairs and recent history, and is significantly stern and serious about the severity of the approaching traffic support scalability challenges. On this subject, traffic news hounds have been hearing reports for many months of some U.S. cities recently reaching complete traffic and transit saturation maximums, including Washington DC.

Now let's hear some example "Did You Know?" bottom lines from the report, some relevant, some just interesting: