Can't help on the topography, but an Official Guide from December 1950 shows the New York Mail, out of Buffalo at 5.45 pm, with a sleeper for New York and a Buffet Lounge car for Elmira (9.29 pm), stopping at Lancaster, East Bethany, B. & O. Junction, Mount Morris, Groveland, Dansville, Wayland, Atlanta, Cohocton, Avoca, Bath, Campbell, Corning, and onward to Hoboken, where it arrived at 5.30 am, although the sleeper could be occupied until 8.00 (in 1945 it also made Kanona and Savona, but they were gone by 1950). Corresponding westbound service was provided by The Owl, leaving Hoboken at 1.05 am (sleeper for Elmira available for occupancy from 9.30 pm, arriving in Elmira at 8.55 am, when passengers for points beyond would move up to a coach). A Diner Lounge car was added at Binghamton. Other than that, the only stops made by other trains were Mount Morris, Dansville, Bath, and Corning. Darien Center and Alden were on the Erie, which roughly paralleled the DL&W as far as Lancaster, but then headed more southerly via Town Line, Marilla, Alden, Darien Center, Attica, Linden, Dale, Warsaw, Rock Glen, Silver Springs, Castile, Portage (Letchworth Park), Washington Hunt, and so on to Hornell, where it joined the Erie main line. The Erie used to have 3 trains a day via that route to and from Jersey City, but by 1950 it was down to one a day in each direction, and the eastbound, which left Buffalo at 5.10 pm, had no Jersey City connection unless you wanted to wait from 8.20 until midnight for The Lake Cities.
When the DL&W built the new line from Binghamton to Buffalo almost every
town on the new line was already served by another railroad. From Wayland to
Binghamton the new DL&W was never more than 3 or 4 miles away from the Erie.
The hill from Groveland to Wayland took the line from around 600 feet
to 1400 feet in elevation. The 390 route is much steeper since it makes
the same 800 foot climb in less than half the distance.
The Dansville station was up a steep road on the East Hill where you
see the "line." Dansville already had more convenient rail service in
the village from the Dansville & Mt. Morris which allowed connections
to Rochester and Buffalo which was as far as most people traveled.
The DL&W allowed passengers in Dansville better rail access to Elmira,
Binghamton, and NY City.
The steep eastbound grade on the hill was not much of a problem for
the DL&W when it was built because the primary purpose of the line
was to carry coal from the Scranton area westbound to Buffalo. When the coal traffic
died out in the 1950's the steep grade doomed what little chance the
line had for survival.
When you are riding up the hill from Dansville on I-390 you can look to your right and see
the abandoned roadbed of the Pittsburg, Shawmut & Northern. It was abandoned
in 1947, but if you look hard you can still see it as you approach the top.