by Sand Box John
"polybalt"
Thank you.
I am 99% sure the top speed allowed by the WMATA signal ATP system was 75mph. Revenue trains could never run above this speed. Of course test trains often ran with the ATP cut out, so might get a little faster. In an attempt to protect the motors from damage there was an overspeed trip function in the propulsion control equipment set slightly higher.
The following is from a WMATA document dated 04-06-2004 that is not publicly published. When I first saw the table of ATS Speed Commands I was surprise to discover that the highest speed command was 79 MPH.
ATS speed commands are used to modify train performance. Speeds are selected to maintain schedules, adjust train performance during inclement weather, etc. ATS speeds are not used for safe train operation and are not fail safe in design. In the event a train fails to receive an ATS speed command, it will operate at the ATP limiting speeds. ATS speeds can only reduce the trains regulated speed and never exceed the ATP limiting speed. ATS speeds are combined with acceleration rates (full or half) to create performance levels. Each station TWC (Train to Wayside Communications) transmitter is programed to transmit only four of the fourteen possible ATS speeds. This will give eight performance levels when combined with the two acceleration rates. Fly-By transmitters, located on the approach to selected stations, are used to transmit an ATS speed command of 24 MPH during inclement weather.
ATS SPEED COMMANDS
14 MPH
19 MPH
24 MPH
29 MPH
34 MPH
39 MPH
44 MPH
49 MPH
54 MPH
59 MPH
64 MPH
69 MPH
74 MPH
79 MPH
The remainder of the document contains tables of "Normalized ATS performance levels for station TWC transmitters" combined with "Inclement weather maximum allowable performance levels".
It was possible to trick the system to get slightly higher speeds. If I remember right, there were two manually operated thumb switches for wheel wear correction, one for the propulsion control and one for the ATP system. New wheels were 28" diameter and allowed to wear down to 25". When the cars got their wheels trued, or replaced, these switches were supposed to be set to the current wheel diameter. When delivered all the cars had new 28" wheels, so setting the switches to the setting for maximum wear could get you another 10% in top speed.
This may explain why some have said they have seen actual speeds displayed on the operators console that were greater then 75 MPH. It also might be an explanation as to why consists of cars from different car series (Rhor, Breda 2000, 3000, 4000, CFA/AAI and Alstom) tend to fight one another when under acceleration.
Thank you.
I am 99% sure the top speed allowed by the WMATA signal ATP system was 75mph. Revenue trains could never run above this speed. Of course test trains often ran with the ATP cut out, so might get a little faster. In an attempt to protect the motors from damage there was an overspeed trip function in the propulsion control equipment set slightly higher.
The following is from a WMATA document dated 04-06-2004 that is not publicly published. When I first saw the table of ATS Speed Commands I was surprise to discover that the highest speed command was 79 MPH.
ATS speed commands are used to modify train performance. Speeds are selected to maintain schedules, adjust train performance during inclement weather, etc. ATS speeds are not used for safe train operation and are not fail safe in design. In the event a train fails to receive an ATS speed command, it will operate at the ATP limiting speeds. ATS speeds can only reduce the trains regulated speed and never exceed the ATP limiting speed. ATS speeds are combined with acceleration rates (full or half) to create performance levels. Each station TWC (Train to Wayside Communications) transmitter is programed to transmit only four of the fourteen possible ATS speeds. This will give eight performance levels when combined with the two acceleration rates. Fly-By transmitters, located on the approach to selected stations, are used to transmit an ATS speed command of 24 MPH during inclement weather.
ATS SPEED COMMANDS
14 MPH
19 MPH
24 MPH
29 MPH
34 MPH
39 MPH
44 MPH
49 MPH
54 MPH
59 MPH
64 MPH
69 MPH
74 MPH
79 MPH
The remainder of the document contains tables of "Normalized ATS performance levels for station TWC transmitters" combined with "Inclement weather maximum allowable performance levels".
It was possible to trick the system to get slightly higher speeds. If I remember right, there were two manually operated thumb switches for wheel wear correction, one for the propulsion control and one for the ATP system. New wheels were 28" diameter and allowed to wear down to 25". When the cars got their wheels trued, or replaced, these switches were supposed to be set to the current wheel diameter. When delivered all the cars had new 28" wheels, so setting the switches to the setting for maximum wear could get you another 10% in top speed.
This may explain why some have said they have seen actual speeds displayed on the operators console that were greater then 75 MPH. It also might be an explanation as to why consists of cars from different car series (Rhor, Breda 2000, 3000, 4000, CFA/AAI and Alstom) tend to fight one another when under acceleration.
John in the sand box of Maryland's eastern shore.