The steel highway... because they hadn't started paving roads, building rock roads like the Romans was too labor intensive, and they were fed up with muddy roads... but hadn't gotten from horse drawn wagons to trucking yet. A blip in the timeline of cargo transportation

Thanks Steve!

Old Butler plank road, doesn't seem to have planks, but they did install a mile of test steel track from Etna Pennsylvania, to Butler, which is now Butler Road, also known as highway 8

https://www.google.com/maps/place/Etna,+PA/@40.6344743,-80.0924574,10.5z/data=!4m2!3m1!1s0x8834f2e989dfc387:0xa79258ddb897f744