This is the final report of the Task Force on Transportation of the first Hoover Commission, dated October 15, 1948. The Commission had 24 task forces, two-thirds of which were contracted out. The Transportation report was contracted to the Brookings Institution and was prepared by their in-house transportation experts, Charles Dearing and Wilfred Owen. The report recommended the establishment of a new, Cabinet-level Department of Transportation.
The Hoover Commission never published this report, because their Task Force on Commerce (chaired by Herbert Hoover himself, a former Commerce Secretary) instead adopted conflicting recommendations to centralize all federal transportation functions within the Commerce Department. The final report of the first Hoover Commission made that recommendation.
Dearing and Owen then published a slightly edited version of the report as a book, National Transportation Policy, through Brookings Press in 1949. (So Brookings got paid twice for the same work.)
This PDF file contains volume I of the report. The much longer and data-centric Volume II was too big to scan, but interested parties can pick up National Transportation Policy at many libraries or buy a copy cheaply through abebooks.com.