 |
Re: BART's new cars: Why hydraulic brakes instead of air brakes?
Author: mook
Date: 05-01-2016 - 13:45
Having used the DC Metro (when it was more or less working, so a few years ago), they had a typical air-brake sound for the final stop and when starting. That could have been air-over-hydraulic, and the primary braking is dynamic. LIRR cars (from the sound) are more obviously air-braked (and considerably under-powered for acceleration compared to DC and BART), though again it's blended (as is common with all passenger rail) with air handling only the final stop.
All-electric is nearly universal on the West Coast, whether streetcar, light rail, or heavy rail. BART must have something unusual going on to use hydraulic for the final stop, unless they want it for finer (??!) control by the computer of the final stop than all-electric typical provides. All-electric also commonly has track brakes, in addition to friction and dynamic brakes on the wheels, for holding the train at a stop and for emergency braking.
Transit practice since at least the 1930s (with PCC cars) has differed from typical railroad practice with regard to brakes. Operating conditions are different.
All-electric is nearly universal on the West Coast, whether streetcar, light rail, or heavy rail. BART must have something unusual going on to use hydraulic for the final stop, unless they want it for finer (??!) control by the computer of the final stop than all-electric typical provides. All-electric also commonly has track brakes, in addition to friction and dynamic brakes on the wheels, for holding the train at a stop and for emergency braking.
Transit practice since at least the 1930s (with PCC cars) has differed from typical railroad practice with regard to brakes. Operating conditions are different.
