In the 80s I read an article about a straight tunnel thousands of miles long. In this thread's context, it could be from Moscow to New York.
Gravity would pull the vehicle in the first half of the trip as it went deeper, accelerating to maximum speed midway. Ascending in the second half of the trip, gravity would slow it. It would need engine propulsion early to get it started, and late in the uphill climb.
To make it almost frictionless, it would need magnetic levitation, of course.