The number of trucks (tractor-trailers) on parts of I-75 has doubled in the last 15 years. "Big Trucks, Big Challenges: As Truck Volumes Soar and Economy Improves, Experts Warn of Consequences" is the report from the Cincinnati Enquirer on the increased volume of trucks on I-75.  Among other things, the Enquirer reports:

Interstate 75 is now the busiest north-south truck route in the United States, making it a modern-day Mississippi River for freight.