Rapid bus (and streetcar) aren't interim steps
It's worth crackplogging this briefly since I was reminded by a discussion on one of the blogs in my list that I hadn't written anything on Cap Metro in a month or so, and I've been meaning to do this for quite a while anyways, expanding on a quick hit I did a while back:
Some folks think we can view either/both of Rapid Bus and streetcars as a "placeholder for light rail", or a "step towards urban rail", or what have you, implying that the investment we make in those technologies is in fact a down payment on a real urban transit system. In fact, though, neither one can be evolved into reserved-guideway transit which is what it would take to get the gains seen in Dallas, Portland, Minneapolis, Denver, Salt Lake City, etc. Reserved-guideway transit, for those not familiar with the term, is any facility where the transit vehicle doesn't need to share space with, be stuck behind, or otherwise compete with other vehicles (usually cars, but could be regular buses too). Obviously this makes a big difference if you're trying to make up the currently huge speed and reliability gap in Austin between transit and the automobile.
Note that unlike my former colleague Patrick Goetz from the UTC, I view reserved-guideway transit as sufficient to garner significant numbers of choice commuters (those who drive to work today) - as it has worked in Dallas, Portland, Salt Lake, Denver, Minneapolis, Houston, etc. Reserved-guideway doesn't mean grade-separated; grade-separated is elevated or subsurface rail, or if you're feeling generous, completely separate surface rail like Austin's commuter rail route (few crossings, and those completely controlled by physical means, not just traffic control devices). Light rail and BRT both accept less separation in return for the huge economic savings resulting from not having to build elevated or underground facilities, and in practice, almost all of the benefit of true grade-separation is achieved on good reserved-guideway designs.
I don't even have to write a long list of reasons, when just the first will suffice - although there are others. Here it is:
You don't run reserved guideway transit in the right lane.
That's really all you need to know to understand this issue. You can't eliminate right turns on any roadway in this country - it just doesn't work. People are used to restrictions on left turns, sure. But no right turns? No way. It's far too ingrained in our driving culture that we pull over to the right to turn, let people out, find parking, etc. (The British probably have a similar constraint against reserved guideways on the left, come to think).
So what's the problem? Both the streetcar system and the rapid bus starter line will be running in the right lane. (The 2000 light rail plan would have run down the middle of the road, at least on the two-way streets like Lamar and Guadalupe). So all the investment in rail (streetcar) and stations (rapid bus) needs to be completely dug up and rebuilt if either one was to be transitioned into any form of reserved-guideway transit, either light rail or bus rapid transit.
That means that building streetcar and rapid bus is actually a step FARTHER AWAY FROM URBAN RAIL, not a step towards it.
And no, a right lane shared by transit and "right turns only" isn't a solution to this problem either. (It's what Honolulu briefly tried to float with their ghastly failure of an experiment with BRT). Trucks pull over to the right to load and unload; so do normal buses; and cars turning right can stop your transit vehicle just as dead in its tracks as a car waiting to go through an intersection can.