Interoperability and Intermodality: Or, Taking More Than One Train or Bus

I was reading recently about intermodal fares, the systems by which multiple modes of transit, and frequently multiple operators of transit, can be (or not be!) experienced as a single seamless whole by their customers through the use of shared payment systems, travelcards, etc.I thought it might be useful to think through how this operates in three different cities I've visited in the past year or so, and what we might take from those cities about how cities in general can make this idea work for them.1. Montréal and the Integration of Legacy and New-built SystemsMontréal appears in the article I was reading, and for good reason: the system allows you to pay based on zones across any transit you take in the city, regardless of what kind of transit you're taking in those zones.This machine can get me tickets to the Metro, where it's located, but also to the buses, the REM, and the local commuter rail. Anywhere on this island is the same zone; how convenient! But what makes this…