The government probably wouldn't have if both rail lines weren't shut down simultaneously.
The Teamsters should take a page from the way the UAW/CAW handles the Big Three; focus negotiations on one, then tell the other "here's the template".
Keeping the rail lines running is too critical for the government to allow a protracted lockout/strike, but a (non-conservative) government would likely allow far more leeway if only one of the railways are shut at one time.