I wrote in January about how the Federal Railroad Administration's antiquated safety rules were blocking the use of diesel multiple units, passenger rail cars that have built-in diesel engines instead of needing to be pulled by dedicated engines. There are only a few DMUs that are compliant with the FRA regulations, notably the Portland Westside line. There are also a few non-compliant DMU services, like NJ Transit's River Line, that have received a waiver from the FRA because the passenger cars run at different times from the freight trains.
Last year Austin's Capital Metro bought a bunch of cars similar to the ones used on the River Line in the hopes of getting a similar waiver for time-separated service, and was being stalled by George Bush's FRA. Now, under Obama, the FRA has indicated that it will work with Capital Metro and grant the waiver if they install steel cages around the fuel tanks.
Time-separated service is not great in terms of accomplishing much of our goals. It gets people to work and back, but has no flexibility for schedules, and they still have to drive for shopping and recreation. It can build a constituency for transit, potentially save families the expense of owning two cars, and reduce congestion somewhat, but it won't shift too many people away from car ownership. However, this change suggests that the FRA may be more open to relaxing its rules for DMUs in general. If that happens, maybe we could see DMUs soon on the New England Central, on the Suzy-Q and even on the Oyster Bay Branch.