Reply to "METRA to Purchase SD70MACs for commuter service."

Krieglok posted:
Hot Water posted:
Dominic Mazoch posted:

And how fast will these locomotives have to go in commuter service?  My guess is they will need to go much faster than passenger trains on the Alaska.

I would think that they should be capable of at least 75 MPH.

They will likely be geared for passenger service rather than freight, giving them a higher top speed. The gearing for passenger locomotives reduces the overall tractive effort for heavy loads but increases the acceleration rate from a standstill as well as giving the higher top speed...

I wish NJT would consider these engines in the future!


For commuter service?  Passenger gearing?  The SD70MAC's have been routinely operating on BNSF at 70 MPH on coal trains and other freight trains on former ATSF territory.  Does METRA operate commuter trains faster than 70 MPH?  And, if so, do the longer, heavier, commuter trains actually have enough time to get up to 75 or 79 MPH between stops and can METRA trains achieve and maintain a speed in excess of 70 MPH for long enough to make any real difference in the schedules?  70 MPH=51 seconds/mile.  75 MPH=48 seconds/mile.  79 MPH= 45 seconds/mile*.  So, as opposed to using a 70 MPH gearing, to shave a minute of running time between stops at 75 MPH, the train has to operate at 75 MPH for 20 miles.  To shave a minute of running time between stops at 79 MPH, the train has to operate at 79 MPH for 11.3 miles.  While speeds above 70 MPH are certainly beneficial to the schedules of most inter-city passenger trains, the shorter distances between stops in commuter service eat up much of the higher speed advantage with the reduced amount of time available to maintain higher speeds.  Also, if a train has to reduce for curves or - worse - to proceed through crossovers (as when weaving through traffic or running around a slower, non-express train), the higher speed advantage is reduced or eliminated.

I'm not saying that there would be any significant additional cost in the rebuilding process (none at all if new ring and pinion gears are specified as part of rebuilding).  I am only questioning whether passenger gear ratios are useful for METRA service, because their purpose is to allow running time to be reduced by maintaining higher speed.

*  These speed/time equations are slightly rounded to avoid using fractions of seconds.  The equations, as presented, are the accepted standard for measuring speed between mile posts.



Superintendent, High Plains Division (O Gauge) 

The Panhandle & Santa Fe Railway Co.

Lone Star Hi-Railers

Santa Fe, All the Way

OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653