BRT (or Rapid Bus) is NOT a stepping stone towards light rail
As part of an excellent series of takedowns of BRT, the San Francisco Bike Blog has written an excellent rebuttal to the frequent claims that BRT or Rapid Bus plans can function as stepping stones towards light rail. One relevant excerpt relating to a transitway in Ottawa that was designed to be convertible to LRT::
The study concludes that with limited financial resources, it is better to invest in new rapid transit corridors than to replace an existing one. It is not considered cost-effective to convert the Transitway to LRT at this time.
Please check out the rest. There's a lot more good stuff in the other links from Jeff's collection as well, including impacts on the urban environment from smelly, noisy, uncomfortable buses versus electric trains.
In our case, our potential investments in our completely useless Rapid Bus plan are completely nonportable to light rail (the stations are on the wrong side, for instance). Ironically, as the linked story points out, every improvement that could be made to make Rapid Bus more like Bus Rapid Transit would make it less likely we'd ever see light rail on the #1 corridor.