The trouble with Manor to Mueller
This is going to be a bit disjoint - I'm typing this at 6:25 at a Pizza Hut in Huntsville, AL (no buffet; waiting for my personal pan pizza; do they still do this?) after having gotten up at 4AM to fly to Nashville and then drive 2 hours down here, then working all day with the other companies on a project for my day job.
After the original unveiling of the streetcar plan promised complete dedicated guideway, ROMA has begun the inevitable backing away process - now saying that dedicated guideway is unlikely on Manor and Congress. Neither one makes sense, but ROMA is likely a believer in the "magic streetcar fairy dust" (note to readers: remind me to write an article on this phenomenon; in short: the theory that streetcars are so great that people won't mind being stuck in traffic). Let's look at Manor in particular.
At the original public unveiling of the plan, yours truly stood up and asked why Manor couldn't be singletracked instead of condemning right-of-way to build dedicated doubletrack. An anonymous jackass on the skyscraperpage forum (who I believe to be either Lyndon Henry or Dave Dobbs) scoffed at the idea, but it's time to consider it again, since ROMA has apparently decided that expanding the right-of-way of Manor is now off the table.
The problem: Manor doesn't have enough width for a car lane each way and one "train lane" each way. (Current configuration is 2 bike lanes, 2 through lanes, and a center-turn lane). There's ALMOST enough width to run reserved-guideway rail and keep one through lane each way if you lose the bike lanes, but not quite. The old configuration of Manor prior to the installation of bike lanes was 4 through lanes, but they were probably too narrow to support car next to train operation (at least, that's what I'm assuming).
ROMA's solution: Run the streetcar in with regular traffic. Sounds fine, right? There's not much traffic on Manor today by any reasonable standard.
Why ROMA's solution stinks: If there's going to be enough traffic headed downtown to fill streetcars in 5 years when a lot more people live at Mueller, there's also going to be a lot more people driving on Manor (which is the smartest driving route to UT, and probably right up there for the Capitol and downtown). So the conditions today that make it look like cars would never slow down the train (much) are misleading - most of the cars that will be there in 5 years aren't there now.
M1EK's solution: Single-track reserved guideway. This stretch is very short (took about two minutes to drive down in the cab on the way to the airport at 4:45 this morning). Initial frequency is set for "every 10 minutes". You ought to be able to keep this as single-track and maintain that schedule with no problems - but if that's too close for comfort, bulb out at a station right in the middle - voila, two shorter single-track segments, and you only need to condemn a sliver of land around that station rather than along the whole stretch.
Why M1EK's solution stinks: Trains will still compete with each other; schedules will suffer.
Why ROMA's solution stinks more: Trains will lose a lot more schedule time stuck behind cars than they will waiting for an oncoming train to clear the single-track section, on average.
Why magical streetcar fairy dust partisans will still dislike M1EK's solution: "You can't expand your solution into dedicated double-track". One track right in the middle of what used to be the center turn lane is right in the middle of where two tracks would need to be - you can't reuse that track.
Why it's not any worse than ROMA's solution on that metric: The rails on which the shared-lane streetcar will run are also going to be in the wrong place - you can't magically change those into reserved guideway either (unless you completely close Manor off to cars). In fact, M1EK's solution allows for a more incremental approach - where you can gradually acquire more right-of-way and shift the double-to-single-track transitions further out away from the station(s).
Does anybody else ever do this? Yes, Baltimore had single-track on their light rail line for quite a while (maybe still do; I haven't kept up to speed on their system).
Congress Avenue is a much easier case, by the way; it's largely an aesthetic objection (reserved guideway should run in the middle of the street, but some people with absolutely no grounding in history are upset about the caternary wires in front of the view of the Capitol - forgetting that for 50 years or more, that's exactly what we had).