To add to this conservation. First, this thread is about DFW transit, not about Austin transit.
I believed Houston's Metro used the wrong type of train on its Main Street corridor. Modern streetcars are much better in traffic than light rail trains.
If your corridor isn't wide enough for dedicated lanes or ROWs, streetcars should be the preferred choice.
Fort Worth plans to use DMUs on active railroad corridors and Streetcars on fairly narrow city streets. Just Fort Worth, Blue Mound and Richland Hills are the only member cities in the T. Richland Hills lies northeast of downtown Fort Worth and already receives TRE commuter rail services. Blue Mound lies north of downtown Fort Worth and only gets bus services. NONE of the other cities and towns in Tarrant County are T member cities.
Most of Forth Worth's expansion recently has been to the Southwest and North. Most of Tarrant County's expansion has been to the South and Northeast. There are ACTIVE freight rail lines in all the corridors, three of which is where the T plans the SW2NE DMU regional rail services. The train technology that must be FRA compliant on ACTIVE freight railroad corridors. Non compliant FRA light rail trains can't be used.
Therefore, all the other directions from downtown Fort Worth in the T's service area are well within the range for using streetcars.
A restriction placed upon the T is finances, they only collect a half cent sales tax. Unlike DART, which charges a full cent sales tax. Therefore, the T doesn't have the financial resources to build a light rail system.
Another restriction, in comparison to DART, is that all the railroad ROWs are ACTIVE, and owned by privately held railroad corporations, except two. One is half owned by DART and the T, the old Rock Island line the TRE runs on between downtown Dallas and Forth Worth, and by the way it supports freight trains all day and night too. The other is the old Cotton Belt coorridor being used by the proposed SW2NE regional rail line, which is owned by DART, which also has ACTIVE freight services.
I think the T is doing fairly well with the financial resources they have. One doesn't need to use 65 mph capable light rail trains on city streets with 35 to 40 mph posted speed limits.
I'll agree having dedicated ROW for light rail trains is a great idea. But when dedicated ROW and lanes aren't available, streetcars is the best choice.
DART on the other hand owns all the railroad ROWs it runs light rail trains on. Some locales along DART owned ROWs still have ACTIVE freight service. DART does not use time separation schemes on its ROWs, instead uses at least three tracks where necessary, at least two electrified and dedicated for light rail trains only, and at least one dedicated track for freight trains only. It's much easier to do this when DART owns the ROWs, it's virtually impossible to get freight railroad corporations to agree to lose any control of their ROWs. You're lucky to get permission to use their ROWs, at a significant cost.
Where DART light rail trains run along city streets, they are in dedicated lanes, which is the way it should be. But note, the light rail trains do not run exclusively down city streets, most of the lines are abandoned, DART owned, railroad ROWs. That's why light rail trains made sense for DART, but is not the best choice for the T to date.
Dallas and DART are also looking at building DMU regional rail on the old Cotton Belt ROW, and streetcars in downtown Dallas streets. Which supports my arguments that the proper train choice depends upon what's best for each corridor, and how big your pocketbook is!
The T's SW2NE DMU regional rail web site:
http://www.sw2nerail.com/
Fort Worth's Streetcar web site:
http://fortworthology.com/lightrail/
NCTCOG's Rail North Texas web site:
http://www.nctcog.org/trans/transit/.../rnt/index.asp