The entire process I try to apply to cost-effective rail construction is to figure out the best places to spend money per unit of time saved. Obviously, this is mainly for intercity traffic – for local traffic it’s more interesting to look at cost per rider – but it’s intercity traffic that benefits most from this kind of optimization anyway.
With the Northeast Corridor, there are definitively low-hanging fruit, such as new (non-FRA-compliant) rolling stock, raising superelevation, improving platform access within present infrastructure, and adding constant tension catenary south of New York. Those are so useful, in terms of cost per benefit to travelers, that they should all be pursued immediately. The more interesting question is what to do afterward. I’ve proposed a few things before, in various posts, but it’s more useful to talk about the general process of determining where to build, i.e. which fruit are medium-hanging and which are high-hanging. I think traditionally this boils down to two parameters:
1. Cost per minute saved, including by improving reliability. This is of course adjusted for demand: New York-Philadelphia minutes are the most important, then Philadelphia-Washington, then New York-Boston, and finally other corridors.
2. Reduction in operating cost. If the rest of the network is based on hourly trains, and you need to squeeze five additional minutes to reduce your travel time including turnaround to an integer number of hours, it’s worth spending the money on it to avoid needing extra trains, or a schedule that doesn’t match up with the rest of the network. (And the same is true if the network repeats every 52 minutes – there’s nothing magical about 60 here.)
However, three additional, less obvious parameters are important:
3. Usefulness to local transit, in terms of speed, reliability, etc. This essentially reduces the cost imputed to intercity trains per minute saved.
4. How low-hanging the fruit becomes if combined with another. The issue is that eliminating two adjacent slow zones in an otherwise fast run saves more than double the time of eliminating just one of the two; another way to think about it is that eliminating the second slow zone saves more time than eliminating the first. This can result in counterintuitive phasing in a constrained funding environment.
5. How high-hanging the fruit becomes if it is delayed. If there is significant disruption to service coming from construction, then it’s better to do it earlier than would be warranted based on pure cost-per-minute-saved calculation.
#3 features prominently in Amtrak’s preexisting planning – in fact, too prominently, with its emphasis on Gateway. It’s a matter of agency imperialism more than anything, but it can lead to good results elsewhere. It’s really points #4-5 that aren’t optimized – either the costs are out of whack, or they are ignored. Washington Union Station‘s remodeling is an example of overemphasizing #5 without considering the cost or the ability to use existing infrastructure more cheaply; Transbay Terminal‘s poor column placement is an example of ignoring #5 entirely.
The reason I push concrete-heavy improvements between New Rochelle and Stamford, but not between Stamford and New Haven, comes essentially from those three points. The Cos Cob Bridge replacement is good because of points #1, #3, and #5; an I-95 bypass of Port Chester and Greenwich then interacts with it positively because of point #4, and also provides a suitable passing segment between high-speed and express commuter trains. In contrast, the projects east of Stamford don’t interact so positively: they involve constructing various bypasses, at high cost per minute saved, in separate locations so that the same increasing returns do not exist, and generally it’d not difficult to connect the bypasses to existing tracks so that the disruption effect of #5 is not in place.