The Vermonter is being replaced by bus service north of Springfield from September 10-12 due to work on an underpass on the Connecticut River Line just north of Springfield Union Station. (The Valley Flyer is being cancelled as well, with no bus replacement, but that's impertinent to my question.) What's the reason the Vermonter can't be rerouted on those days over the route it used to take, via the former Boston and Albany to Palmer and the New England Central to Brattleboro?