Noel Weaver wrote:The New Haven - Derby route never really had that much traffic. Passenger service was local in nature and the through freight trains ran via Devon because it was much better physical plant, a better route through New Haven, multiple tracks and not nearly as severe grades. Curves, clearances and bridges also were a factor and the heavier locomotives could not use this line either. I doubt if it would have served any useful purpose in recent periods. Waterbury - Hawleyville was also much shorter but again the grades killed that route and that route could support heavier power. In earlier years the New Haven and many other railroads in the northeast had just too many lines that traffic could not support and New Haven - Derby fits this catagory.
Just wanted to expand a bit on what Noel said. The New Haven & Derby was basically built to be a nuisance to the "Consolidated" (the New York, New Haven & Hartford.) Originally it was meant to link up to a Hudson River bridge at Bear Mountain-- which was never built. After that it served as a connection between the city of New Haven and non-NYNH&H rails-- first to the Naugatuck Railroad at Derby Jct., then (after the Naugy was leased by the New Haven in 1887) to the Housatonic via a branch to Botsford. As Noel points out, the line cuts straight across hilly country between the two cities: if you look at the route on the 1892 topo maps at historical.mytopo.com, you can see that in 9-odd miles it climbs from sea level at New Haven over a couple of 200 foot ridges before dropping back down to near sea level at Derby.
Like the Bethel-Hawleyville branch of the Housatonic, this line basically had no purpose anymore once everything it connected to was part of the New Haven.
The Connecticut Company's New Haven-Derby trolley line, which (I believe) followed the alignment of Route 34, would probably have been better suited for suburban use-- but that's a subject for a different board...