Proposed E-line extension Heath St. to Hyde Sq.

highgreen215 wrote:I'm not sure if it is signal priority, but on Beacon Street there is now Green Line signal coordination which works pretty well.

There isn't signal priority on Beacon. Brookline offered to put it in and foot most of the bill and the T balked at installing sensors on the tracks that would let the light system know when trains are on the tracks. Brookline has actually investigated using a camera system to detect trains thereby giving them signal priority whether or not the T wants it but those systems are less reliable.

It's too bad the MBTA balked at it.... they could use the track sensors for a real time data feed for countdown timers. It would probably be less expensive than installing GPS in every car.

F-line to Dudley via Park wrote:but also future-proofs the Ashmont Branch for the power requirements of next-gen Red Line cars.

Why should new subway or light rail cars use more electricity?

Automobiles, buses, and diesel trains have been getting more and more efficient over the past 40 years. In fact, it's been a big priority for the federal government. Surely electric trains can do the same.

diburning wrote:It's too bad the MBTA balked at it.... they could use the track sensors for a real time data feed for countdown timers. It would probably be less expensive than installing GPS in every car.

I would have balked at it too ! It's very likely that the town of Brookline was going to set up the State (T) by using figures compiled regarding service in a law suit whereby an unfair comparison to Boston figures would be entered as "evidence". At the very least, it would have given an agency outside of the T a real basis for demanding changes.

boblothrope wrote:

F-line to Dudley via Park wrote:but also future-proofs the Ashmont Branch for the power requirements of next-gen Red Line cars.

Why should new subway or light rail cars use more electricity?

Automobiles, buses, and diesel trains have been getting more and more efficient over the past 40 years. In fact, it's been a big priority for the federal government. Surely electric trains can do the same.

There's a whole lot of reasons for increased power requirements, and only part are the trains themselves.

Electric motors can only get so efficient; even when you consider modern innovations like brushless motors, you're hitting diminishing returns as you near 100% efficiency. That's a whole lot different from combustion motors where you can often pull an extra 10 percent out by improving the design some.

Trains are also getting heavier. That's a function of stricter crash requirements, more electronics, etc. More power available allows heavier trains to accelerate faster - take a look at BART's acceleration sometime.


But the Red Line is not going to run 6-car trains on 4.5-minute rush hour headways at existing speeds forever. I'm not sure what the minimum headways the system can support are, but with proper signalling the could be a whole lot smaller than 4.5 minutes. According to Sand Box John, the DC Metro can dip a lot lower than that: "The train control and signaling system is designed to accommodate 90 second headways on the trunk portions of the system*, WMATA presently operates 180 second headways with a mixture of 6 and 8 car trains." With sufficient rolling stock and some infrastructure upgrades, 3-minute headways during rush hour would do very good things about overcrowding.

Someday, if headways cannot be pushed low enough, they might need to start running 8-car trains. That's a whole lot of renovations, but it's something they've done before. If we ever see extensions to Brockton or Waltham it might be necessary.

Additionally, with new rolling stock, we might be able to see higher speeds particularly on the Braintree Branch. Power draw increases faster at higher speeds.

The new Blue Line cars are the most efficient in the system. Other than new composite materials optimizing strength and weight ratios, the biggest energy saver in the new cars is the regenerative braking system which, instead of burning off that excess energy in resistor grids, actually send that power back into the overhead which could be helping to power another train accelerating somewhere down the line. I don't know how we got onto this, but if we're going to go off topic, we may as well do so accurately.

It's a win-win for the T as by law, the power company has to buy the power generated, which probably amounts to a credit on the T's electricity bill. A big advantage to buying, instead of producing their own power, like they used to do on 1st St.