CTA Subway Cars Braking System

Which of the older chicago subway cars uses rehostatic/camshaft braking and which of the newer subway cars uses the regenerative/chopper braking system and finally what type of bizzing sound will I hear when the train is accelrating or braking?

All of the current fleet use a non-regenerative dynamic braking system, along with the now-retired 2000 series. The PCC cars before them were part electric, part mechanical braking, and the cars before them were entirely pneumatic. A test was conducted on a set of 2400-series cars with chopper control upon their delivery in the 70s, but it caused magnetic interference with the ATC system, so the cars in question were converted back to the regular SCM camshaft control. However, the just-ordered 5000 series will be equipped with AC motors, with regenerative braking. So no CTA car has chopper control or regenerative braking yet, but there will be a whole bunch within five years.

The current fleet uses essentially the same type of brakes as the PCC cars ... just a little more modern design. Electric (i.e., dynamic) braking provides most of the deceleration effort, with mechanical brakes (a combination spring-loaded/hydraulic system, if I recall) for the final stop after the dynamic brakes fade. Both types of cars also have electromagnetic track brakes for emergency braking effort. Byte is correct that the cars before the PCC's employed entirely pneumatic brakes -- in most cases, 23-type automatic air.

The cars in service today are relatively quiet while accelerating and braking. When the AC motor cars arrive, you can expect to hear more noise. What kind of a buzzing sound? Well, it'll probably sound kinda like "buzzz-zzz-zzzzzzz" while accelerating and "buzz-zz-zzzzzz-zzz" while braking.

Mike's right about the noise. Supposedly in New York, you can tell who made the AC electrical gear on the newer cars by the noise the car makes.

The dynamic brakes fade out about three MPH. At that point the hydraulic disc brake stops the car. It is interesting to note that the hydraulics hold the brakes in release. The caliper is similar to a truck actuator which uses air pressure to overcome spring tension. High speed trains in Europe and Asia use eddy current magnetic brakes which slow forward progress through magnatism withput contacting the rails.

AC Inverter buzz: Check out this video of South Shore cars, specifically at 22 seconds and 38 seconds. You can hear the inverter whine kick in.
http://www.youtube.com/watch?v=mdlm3JAbTQQ