Where the Eastern Corridor link is likely to fall down is:
1 With poor interconnection to other public transport. The distance between connecting stations will be more than optimum and a tortuous connecting route will be made. Almost as if they are contracted per m of walkway.
2 Inconvenient stations
3 A service that does not meet original promises. If we take the airport rail system, the original fast trains from the airport seem to have been cancelled. They run slightly too infrequently, so can be crowded. Although, to be fair it's usually OK.
Incidentally, if we take the Khon Kaen case, of course a better rail service might increase passenger numbers slightly. They could even draw in passengers from around the region, except of course, the "new" bus station in Khon Kaen is outside the city ring road & nowhere near the station. It should be underneath that rail station.
