The argument has been made that the Budd RDC was “unsuccessful”, but how unsuccessful was it?
Its main market was to replace the 10-Wheeler-with-a-combine-and-a-coach consist in local and branchline service, and it did this quite well. Only the RDC was introduced at a time when those branchlines were drying up, if there ever was a time when they were a cost-effective proposition.
These branchline trains, whether propelled by 4-6-0 locomotive or by underfloor 2-stroke Detroit Diesel, were in turn superceded by bus lines, which in turn were superceded by “friend or relative giving you an automobile ride from Algoma to Austin-Straubel in Green Bay.”
The “standard” Amtrak corridor consist for the longest time had been a push-pull of a Genesis locomotive followed by 4 Horizon or Amfleet cars with a depowered F40 “cabbage car”, ballasted with cement to sit right on its springs with the prime mover removed, bringing up the rear.
So you have 250 tons of locomotive/cab car attached to 240 tons of corridor passenger stock? With no attention paid to streamlining, especially the height steps between locomotive and train car and the underbody of the train car, and tell me if you see this same thing on an intercity motorcoach on something run at lower speed (70 MPH vs 80 and soon-to-be 110 or even 125 MPH for the train). And this is more cost-effective than a consist of DMU’s using off-the-shelf truck engines and transmissions?
I got scolded by someone in the local passenger-train advocacy group that I wanted to kill train crews (and passengers) by replacing these overweight over-powered consists with DMUs where driver and front-car passengers are exposed in a grade crossing collision.
There was a time in the 1990s when Alan Cripe was promoting a Diesel (i.e. DMU) version of the United Aircraft TurboTrain, which in turn was a gas-turbine version of a Diesel-motor-train proposal by Cripe for the C&O in the 1950s.
Budd didn’t aim the RDC strictly at the branchline and local services, it just turned out that way. Consider the “Daylight Speedliner” on B&O and the proposal for bus-frequency service with RDC’s on the ATSF Transcon. The “Daylight Speedliner” got caught up in the general decline of passenger service and the ATSF proposal died after the RDC derailment on the Surf Line, which caused ATSF to sour on RDC’s.
I’ve spent a lot of time in Ireland and the UK over the past two years. Both countries, especially Ireland, use a large number of DMU. I understand the maintenance issues of 1 locomotive versus engines under every coach. There must be a reason that DMUs are welcome in these countries but not in the US.
I was going to mention how both railways handle food differently then Amtrak but the topic of eating and riding trains seems to be very emotional!
What makes you think that the hard riding was intrinsic to adapting a bus body and had nothing to do with a naive design for a 4-wheel passenger car that did not take into account rail-wheel dynamics?
Historically extremely lightweight cars have had poor ride qualities. It seems that the minimum spring rate for trucks to operate successfuly is too high to give good ride qualities to very lightweight car bodies.
Historically, rail-wheel dynamics and getting good ride quality at speed was purely cut-and-try with theoretical treatments by Carter and others not widely known.
These days with the emphasis on HSR by our major trading partners, people engaged in designing new passenger trains better know what they are doing. Much or most of the passenger trains outside US borders are “lightweight” by US standards and ride smoothly, although maintaining the track and especially the surface profile of the rail head has something to do with it.
The Aerotrain was a particularly naive design (as in not understanding underlying physical principles) that rode especially badly. So a GM bus (back in the day) rode on 2 axles and was reasonably smooth. Let’s take a bus body and put two rail-wheel axles on it along with those bus air springs. Same thing?
Not the same thing. The vehicle dynamics that steers a bus are entirely different from those of a rail vehicle. Leaving aside the steering corrections from the human driver, the rail vehicle has solid axles connecting pairs of wheels (in everything apart from Talgo) that exhibit “kinematic hunting.”
The Talgo train sets are light weight and ride on a single axle between cars and ride well. So it can be done. Takes significant maintenance.
Also, when in Great Britain, rode in DMU’s that met and combined into longer trains of DMU’s enroute to London. On the former BCRail from Vancouver to Prince George, they routinely ran a four car train of RDC’s out of North Vancouver to Lilloett, dropped two cars which returned to N. Vancouver while the front two continued North to Prince George. Great operation. Cost effective. But time cought up with them. The RDC’s wore out and it was before the Colorado Railcars.
But my understanding was that the ‘observed’ problems with the Aerotrain’s ride had little if anything to do with kinematic hunting, except insofar as it ‘coupled’ mechanically into oscillation of the carbody in the vertical or horizontal plane. The issue with the Aerotrain (again, as I thought) was lack of effective damping on motion in those planes, particularly the vertical plane, perhaps leading (with high ‘exciting’ energy from lack of bus ‘primary suspension’ in the tires) to bouncing the air springs. This is where the lightweight ‘bus body’ construction becomes a critical element in ride quality that no amount of careful suspension design that does not involve damping or perhaps resonance breaking can help. Something I have not seen discussed in books on the Aerotrain was the exact nature of the 'substantial ‘improvemenst’ GM made on a car inserted into the Aerotrain after it started operating in the West (did I not read this in the Kratville book on Union Pacific streamliners?). This was touted by GM as providing much-improved ride quality. What did the improvement consist of, and what was the stated (or implicit) logic behind it? Are there clear pictures that show the improved design and its features?
More interesting to me are some of the dynamical reasons why the “Michelines” failed over here although at least a qualified success in France. The design implicitly depended on deflection of the ‘tread’ to produce the self-steering without continuous tread contact (my father told me about railfans in the '70s who redi
I’m late to this thread and have only skimmed the replies, but I see no mention of the DMUs already enjoying success on commuter systems in Austin, TX, Ottawa, ON, in Southern California (connecting with Coaster service north of San Diego) and a few others I can’t recall. Can anyone who’s ridden any of these systems give a first-hand account?
As mentioned already, DMUs work best on more lightly traveled lines (branches), not heavily traveled systems like Coaster, METRA, Metrolink, etc.
Other examples includ one near Portland, OR,that connects with and extends the reach of the light rail line running west of the city, and New Jersey Transit’s Trenton - Camden River Line.