LIRR Cab signal Indicator

[workextra]

Can anyone here with documentation explain the reason LIRR chose to go with the Numeric cab signal indications and not the position light aspect as the PRR has done when first installed?
Older LI CSI units had a (MAS) (30) (15) or a (12) 3 aspect indicator
Where as the PRR units and the aspects actually displayed and not the signals speed.
(Clear) (MAS)
(Approach Medium) (60*)
(Approach) (30*)
(Restricting) (15/20) for slow speed aspects and restricting.
* not sure what speed the PRR associated with their signal aspects.

Thanks for you help.

[DaveBarraza]

Can't answer the why part but my 1954 rule book says the cab signals would display 281, 282, 285, and 290 with "aspects, indications and names the same as for fixed signals shown in these rules"

From here https://en.wikipedia.org/wiki/Pulse_code_cab_signaling:
282 in the cab was speed controlled to 45,
285 was 30
290 was 20

[Kelly&Kelly]

First installation was on the Port Washington Branch in 1951. Something about closing the barn door after the horses got away...

[fcqjx]

I think somewhere on this forum that early 3 aspect system changed the 12 to 15. One question I've had for a while is did those 3 aspect systems decode the 120 "approach medium" code used in the 4 aspect PRR system? Did PRR use 120 codes between Harold and A? If so what was displayed on the LIRR's 3 aspect indicator when encountered?

[Head-end View]

I distinctly remember seeing the aspect display unit in the vestibules of the old MP-54 cars just before they were retired circa 1971. There were three lights: 15, 30, MAS. That's all folks. One old-school engineer from back then was quoted as saying the the "MAS" light unofficially meant maximum available speed, not maximum allowed speed. LOL

[ExCon90]

I always believed that when the wayside signal displayed Approach Medium the track contained the MAS code up to a code change point farther along in the block, where it dropped to 30. Was that the case, and is it still?

[DaveBarraza]

I always believed that when the wayside signal displayed Approach Medium the track contained the MAS code up to a code change point farther along in the block, where it dropped to 30. Was that the case, and is it still?

LIRR liked to put code change points in mid-block, to keep the trains moving faster as long as possible. It helps throughput. The practice continues, although due to some more conservative assumptions about train braking performance these days downgrades from MAS to 30 are more common than MAS to 45 then to 30.

[ExCon90]

Thanks for the clarification.