This post originally appeared on Orphan Road.

The process of forecasting transit ridership 30 years in the future mystifies me. I understand there are all sorts of sophisticated computer models and such, but it seems like it’s so massively dependent on so many other factors (how do we know what gas will cost next month, let alone next year, for example?) as to defy prediction. But hey, that’s just a layman’s reaction.

Nonetheless, while persusing Appendix C of the ST2 plan (c’mon, I’m not the only one, right?), I noticed that Sound Transit is being pretty conservative with its ridership estimates.

The way they’ve saved their PDFs makes it impossible for me to extract the text without retyping, so I’ll summarize. They note that they have not taken into account the phenomenon of “rail bias,” which is the fact that passengers are more willing to ride a train than a bus, even if the bus is just as fast. Or, as the document puts it, “passengers know trains can take them only where the trasks are laid and that if they go in the wrong direction backtracking is easy.”

More significantly, the model doesn’t take into account “land use changes resulting from transit investments.” In other words, it doesn’t assume that developers will build residential and commercial developments around train stations, even though that’s pretty likely, and, in fact, already happening around the light rail stations in Rainier Valley.

It’s reasons like this that make you pretty optimistic about ridership projections. Especially when you consider that the Tacoma Link Light Rail beat its 2010 ridership projections just three months after it opened.