CBTC is a Scam and the MBTA Backs Me Up

Communications Based Train Control promises higher capacity at lower costs thanks to the magic of WIRELESS TECHNOLOGY!  However almost every real world situation that makes use of it seems to wind up costing a ridiculous amount, having major reliability problems or both.  It turns out that with signaling there is no free lunch, but when faced with overcrowded subway trains, planners can't help but get seduced by those lovely braking curved.  I mean fixed block, that's so 1890, surely we can do better!

In 2016 the MBTA was conducting a capacity study for the Red Line, which currently has a somewhat anemic throughput of 13tph in the peak period.  With new rolling stock on order, the (T) would literally have more cars than it could run.  The current signaling system made use of fix block audio frequency cab signals installed in the 1980's.  This is similar to many other transit systems such as the CTA, WMATA and BART.  Of course CTBC is the to go technology for capacity expansion and the study quickly confirmed this.  Oh wait, it didn't.

• A detailed analysis assuming a moving
block CBTC system on the Red Line was completed.

• Analysis found that a CBTC system would produce
an improvement of just one train per hour beyond
the improvement from the new cars and minor
system changes.

• Major Red Line capacity improvements can be
achieved without implementing very costly CBTC. 

• Long dwell times in the downtown area and close
spacing of stations limit CBTC as much as they
limit fixed block systems.

That's right, just like the costly NYC Subway L Train CBTC system only increased capacity by 2 trains per hour, applying CTBC to the Red Line would only improve capacity by 1 train per hour over a fixed block alternative.  Past a certain threshold capacity is limited by dwell time and the efficiency of terminal interlockings. The study also found...

• The shorter the block length, the closer the
system is to the ideal CBTC (moving block)
braking distance

• MBTA block lengths in the central subway already
average less than 500 feet (6 car trains are 416
feet long)

It's nice to see that for once a transit agency actually ran the numbers and decided that CBTC just wasn't worth it.  It turned out the best way to increase the capacity was simply to allow the new rolling stock to use updated braking curves that will result in later braking and more aggressive cab signal speed stepdowns.  Also the 1980's audio frequency cab signal system will have its components replaced with digital versions that have faster reaction time and thus allowances for less conservative block progression.