While transportation is a major contributor for emissions it is about half of the amount for electricity and heat production (in the U.S.).
As far as flying, according to a study done by Univ. of Michigan's Transportation Research Institute, flying used to be much more energy intensive to transport people than cars (about double in the 1970s).  However by 2000, airline travel (3,892 BTU per passenger mile) required less energy per passenger-mile than driving (3,926 BTU per person, per mile.) which equates to a lower per passenger-mile GHG emissions.  By 2010, flying burned just 2,691 BTU per passenger mile while cars remained about the same, resulting in that flying was 43 percent better than driving the average car in 2010.  In addition, as fuel is their second largest cost, airlines have a very large interest in continuing that trend.

So where do you put more of the resources and efforts?  Power plants and cars or planes?