Fixed guideway transit's intended user group

The intended user-group for fixed guideway transit is (and has always been) the relatively affluent exurban commuter from the peripheral suburb, able to afford the daily fare. This has been the truth since the first omnibus; if you were poor, you walked, and mechanical conveyance was either a treat or an urgent necessity. But urban transit was magical--it made it possible for many more people to afford to live beyond walking distance of their workplaces, away from industrial smoke, noise and pollution, with more space and better infrastructure (1).

But fixed guideway transit enjoys the special magic of the network effects. Adding node C to path AB not only makes journeys from B to C, but also A to C. So there is an inherent non-linear scaling (2) to adding links. That non-linear scaling is what has made is possible to serve people at lower costs--serving additional journeys on existing infrastructure makes it possible to offer a lower per rider cost than was initially feasible for the first link of your network alone. (In transit history, this surplus is largely supplied by keeping fares fixed when they would otherwise have risen in proportion to costs, rather than lowering them). 

But never lose sight of the fact that it is the middling-affluent that fixed guideway transit was designed to serve. Just as the fares from first class passengers make the flight feasible for everyone on the plane, the feasibility of serving the middling-affluent is what makes fixed guideway transit feasible. 

This has a number of implications for the necessary characteristics of fixed guideway transit. It has to be safer, more comfortable, or faster than the alternative. Historically, that meant things like enclosed carriages, smooth rails, and higher speeds. And in the modern era, that means being faster than the car. Which is something that is very very difficult to achieve, because for most transit trips, the access mode is not going to be a car--it's going to be walking, which is slower. So transit is faster primarily where either the access or egress journey is short--either you live (3)  a short walk away, or you work a short walk away. 

However, there is a special case where fixed guideway transit is faster than driving, and that's when parking is difficult to find. Then drivers face an egress journey (from vehicle to destination) that either requires a long walk, or a long search for parking. (The entire existence of on-site parking is predicated on reducing the parking search-time as a means of improving access). Of course, when demand exceeds supply, there is money to be made, and so paid parking naturally follows (4).

So when thinking about where to add fixed guideway transit, look to where parking is difficult and/or expensive. But even with Parkopedia, that's still difficult to do (especially given the heterogeneity of the terms of parking). But Google Earth easily furnishes a strong symbol of where parking is expensive--structured parking garages. Larger garages are more efficient than smaller ones, so garages tend to be sited where there is a lot of demand, and where they are located is within a short egress-walk to the ultimate destination. There is no need to analyze employment density--someone else has already done the analysis and made a multi-million dollar investment on that basis, when they built the parking garage. 

(1) Retrofitting an urban environment with underground sewerage always requires a megaproject, a cloaca maxima for a network capable of serving everywhere upstream. So moving to someplace provided with (mandated to have) underground sewerage is a win from go.  

(2) A broader topic, but in essence: each link adds more because of the network effect, but each link is less-good than the last, because you always build the best links first. So at some point, any network faces declining marginal returns on expansion. 

(3) 'Station cars' are a novel case where someone lives near transit, and then uses a low-end vehicle to make the post-egress journey for the last mile. Employment being more concentrated and more central than population, most park-and-ride lots serve the access-to-transit part of the journey.  

 (4) "Free Parking" merely shifts who pays - maybe it's the retailer, maybe its your employer, maybe it's the local polity. Urban space is valuable, and someone has to pay the piper.