Why commuter railroads won't run diesels

Earlier I talked about why freight will never electrify their railroads. Now I'd like to show, by way of an example, why commuter railroads won't run diesels in the future, choosing instead to electrify their lines. There are a couple of reasons for this.

Firstly, operational costs have a far greater prominence than do capital costs owing to the nature of government agencies as opposed to private agencies. An investment that is hard to justify for a freight operator becomes much easier for a public agency that is receiving "free" funding from another agency and in the process is able to reduce its operational costs to those to whom it is immediately responsible. In such a way does spending hundreds of millions of dollars to save a few million per year become an attractive financial option.

More importantly, however, is the fact that electric trains accelerate much faster, and electric multiple units, compared to a diesel locomotive hauling several rail cars, accelerate like a bat out of hell. The Fairmount DMU study gives the acceleration characteristics of a diesel push-pull train set such as MBTA and other commuter agencies use. Accelerating to 60 miles per hour takes 166 seconds; by extrapolation of the acceleration trend, 80 miles per hour would take 301 seconds. That's significantly slower than the Talent DMU that my last post featured, but look at it in comparison with a Stadler FLIRT:

The FLIRT reaches 60 miles per hour in only 27 seconds, over two minutes faster than a traditional American train set and reaches 100 mile per hour in about 76 seconds, a minute and a half before our vaunted American train has hit 60 miles per hour (it's just about to hit 35 miles per hour). It also breaks significantly faster.

In this video we can see a deceleration from 70 kilometers per hour to 10 kilometers per hour in 9 seconds, which is an average braking rate of 6.67km/h/s or 4.145mphps. This NTSB report on a Metrolink train exceeding a stop signal reports:

The third test used the service air brake and dynamic braking but did not use the emergency brake. The brakes were first applied when the train reached 74 mph. In this test, the brakes were applied in increments, as in the first test; however, there was less time between brake applications. The total stopping distance was about 2,490 feet.

Working backwards from the stopping distance equation on page 21 of a Department of Defense study on using TGVs to haul M1 Abrams tanks, the train's stopping rate is only 1.62mphps, about 40% that of the FLIRT.

The upshot of this is that more time is spent at higher speeds, reducing the time penalty for any individual train stop and greatly increasing the average speed, making it more attractive to travelers and increasing its patronage, and political support, as a result. By way of example, I ran a calculation of trip times using the Stadler FLIRT, as demonstrated in the above videos, to see how this would affect Metrolink's schedule between Laguna Niguel, the most southern point on the OC Line where NIMBYs and single tracking are not a concern, and Los Angeles Union Station. For this purpose, the use of Metrolink and BNSF timetables was invaluable. I assumed a 30 second dwell time, that unless it resulted in only ~.1-.2 miles of cruising acceleration to and braking from the maximum legal speed were called for and that all curves were accounted for by the speed limits. Additionally, while it is not always true, it was assumed that the mileposts were accurate and that they did equal a true mile. Briefly following is all the speed limits, to save others the trouble.

Laguna Niguel-Irvine: 8.7 miles (MP 193.7-185) 90mph all miles
Irvine-Tustin: 5.5 miles (MP 185-179.5) 90mph all miles
Tustin-Santa Ana: 4.3 miles (MP 179.5-175.2) 90mph till 176.1, 50mph after
Santa Ana-Orange: 2.6 miles (MP 175.2-172.6) 50-174.7, 79-173.8, 40-173.2 60 after.
Orange-Anaheim: 2 miles (MP 172.6-170.6) 60-172.4, 35-172, 79 after
Anaheim-Fullerton Jct: 4.4 miles (MP 170.6-165.4) 79-170.4, 70-169.2, 79-165.9, 55-165.4
Fullerton Jct-Fullerton: .4 miles (MP 165.4-165) 79mph
Fullerton-Buena Park: 4.7 miles (MP 165-160.3) 79-163.8, 75-163.5, 79-161.1, 70-160.8, 79 after
Buena Park-Norwalk: 4.2 miles (MP 160.3-156.1) 79-156.6, 75 after
Norwalk-Commerce: 7.6 miles (MP 156.1-148.5) 75-155.9, 79-154.2, 70-153.8, 79-153, 50@153, 70-152.5, 79-152.1, 50@152.1, 79-151.7, 65-151.4, 79 after
Commerce-Soto: 4.1 miles (148.5-144.4) 79-144.5, 40 after
Soto-LAUS: 4.2 miles to CP San Diego JCT (144.4-140.2), 0.2-CP Mission (MP 0.8), .8 to LAUS (MP 0.0).
144.4-142.8 44mph, 142.8-141.2 79mph, 141.2-140.8 45mph, 140.8-140.2 35mph, 0.8-0.5 25mph

The current schedule reads as follows, adjusting to make a Laguna Niguel departure :00 (using train 603)
0:00 Depart Laguna Niguel
0:09 Irvine
0:16 Tustin
0:23 Santa Ana
0:28 Orange
0:32 Anaheim
0:41 Fullerton
0:47 Buena Park
0:55 Norwalk
1:05 Commerce
1:19 Arrive Los Angeles (there are 7 minutes of padding which makes scheduled time 1:26)

Calculated with a FLIRT:

Laguna Niguel-Irvine

Leaves 0:00:00 arrives 0:06:18 departs 0:06:48

Tustin-Irvine

Leaves 0:06:48 arrives 0:10:58 departs 0:11:28

Tustin-Santa Ana

Leaves 0:11:28 arrives 0:15:20 departs 0:15:50

Santa Ana-Orange 

Leaves 0:15:50 arrives 0:18:52 departs 0:19:22

Orange-Anaheim

Leaves 0:19:22 arrives 0:21:42 departs 0:22:12

Anaheim-Fullerton

Leaves 0:22:12 arrives 0:27:16 departs 0:27:46

Fullerton-Buena Park

Leaves 0:27:46 arrives 0:31:46 departs 0:32:16

Buena Park-Norwalk:

Leaves 0:32:16 arrives 0:35:52 departs 0:36:22

Norwalk-Commerce:

Leaves 0:36:22 arrives 0:42:29 departs 0:42:59

Commerce-Los Angeles:

Leaves 0:42:59 arrives 0:53:25

Obviously in practice and as put on a schedule, the gains would not be as great, but it does indicate gains of up to 26 minutes from Laguna Niguel to Los Angeles Union Station are possible. This is, in many respects, a best-case scenario. The FLIRT is among the best accelerating train sets, it would require a waiver to operate in the United States, and it has limited seating rendering it somewhat less suitable for commuter operations (a six car unit has 260 seats and while American commuter seating density would raise it to about 425-450, a comparable bilevel six car set offers nearly double the number of seats). While multiple-units can alleviate this, it would require greater staffing, Metrolink's contract, which is similar to Amtrak's, requires an additional conductor if there are more than six cars. 

I'll also admit that I can't shake the feeling I messed up the partial braking calculations, although it shouldn't greatly affect matters; at most I suspect it would counteract always rounding up acceleration and braking distances to the next tenth of a mile.

That, in a nutshell, is the advantage which electrification offers alongside fuel savings: a 33% reduction in travel time and making commuter rail operations truly time competitive with car travel. In this particular instance, the cost would be about $500 million or less for the electrification, plus the cost of train sets (Hungary recently purchased four FLIRTs for 20 million euros), and much of the electrification cost can be covered through the California High Speed Rail program, making the burden more manageable on OCTA and the other Metrolink member agencies.