This is an excellent article from the Tennessean. Most cities that developed a Bus Rapid Transit system did not dedicate a lane for a loading platform and a dedicated lane going both direction. Some did that for only part of the way and some not at all. There are various options for a BRT that would not take two or more lanes of traffic and reduce remaining traffic lanes to a nine foot weight the way the Nashville AMP would do. Nashville's design is only slightly faster and million and million of dollars more expensive than alternative designs. See this article for an explanation of alternative designs and examples from other cites using other design options. Nashville never did a study comparing other options.
Could there have been middle ground on Amp's center-lane design?
By Josh Brown, The Tennessean, Jan. 25, 2014- At the center of the controversy over Nashville’s proposed $174 million bus rapid transit line is the question of whether stretches of a busy road now used for cars should be converted into bus-only lanes.
Opponents of the 7.1-mile line proposed for the West End/Broadway corridor connecting West and East Nashville say taking away space for cars on already congested streets will make traffic worse, not better. Metro officials contend the dedicated lanes let buses avoid traffic and are keyto the Amp’s success.
But unlike other cities with such projects, Nashville never analyzed whether a bus line with the same mass-transit-style features — such as stations with level boarding platforms and pre-purchased tickets — would prove just as effective without the bus-only lanes.
That question lingers as engineers move forward in the coming months on a $7.5 million engineering phase that could largely settle the design of the proposal. (link)