Indianapolis has to one of the more egregious examples given how it has a population of circa 1 million, is located in close proximity (by US standards) to other major population centres (Chicago, St Louis, Louisville, Cincinnati and Columbus), has favourable topography for building railways and is home to Amtrak’s main maintenance facility, yet receives just three trains per week (The Cardinal from New York to Chicago via Washington) and has no trams or commuter railways.
Amtrak at least seem to have ideas of how to fix the situation. They released a plan of long term aspirations a while ago that included daily Cardinal service and four trains a day from Chicago to Louisville and another four from Chicago to Cincinnati, with linespeed increases to 110mph between Chicago and Indianapolis.
Another study of long distance routes recommended the reintroduction of the National Limited from New York to Forth Worth via Pittsburgh, Columbus, Cincinnati, Indianapolis, St Louis and Oklahoma City.
If all of that came about it’d go a long way to improve the city’s connectivity. It is a bit odd that St Louis, a city with less people than Indianapolis that is further away from Chicago can have a 110mph line to Chicago with multiple trains per day, yet Indianapolis is stuck with three trundling trains per week.
2022 Corridor ID study routes
Long distance route study. See p.71 onwards