I fail to see why we need to constantly "test our limits" with construction projects alone. The current trend seems to be to build really tall buildings, with the Burj Khalifa in Abu Dhabi as the current holder of the title, and the Petronas towers in Kuala Lumpur as the tallest twin towers.
There are constant efforts to delve into the various unknowns of every science.
Strictly speaking, a "Transcontinental Railroad" has never existed in the US. What we call by this name began in Omaha and San Francisco. The Central Pacific/ Union Pacific connected with other railroads eastward from Omaha.
There never has been a single coast-to coast US railroad, just connections between various companies. There IS however a single railroad that comes close to linking both coasts: the Canadian Pacific links the St Lawrence seaway with Vancouver.
The CP owns a lot of tracks in the US. It is run by the Canadian government. Oooh! A Socialist enterprise!
I really doubt that it would be impossible to build a transcontinental railroad due to OSHA restrictions. That is stupid teabagger talk.