Roadrailers vs. Piggybacks

[Anonymous]

There was a topic recently on roadrailers and I wondered are piggybacks used as an alternative to roadrailers? It seems to me that they have the same use. Maybe someone can explain why use a roadrailer and not a piggyback or vice versa. Thanks.

[DPD1]

Trailer Train is still much more widely used than roadrailers. I think the initial idea was that roadrailers would eventually replace trailer train cars. Obviously there would be a huge savings, not only because of the lack of rail cars needed, but in less fuel used to pull the lighter trailers. I'm not sure of the exact reason why it doesn't seem to have caught on. In some ways, it almost seems to be dying. I have heard that apparently the trailers can sometimes be problematic in yards because of their light weight. I'm not sure if that's true, but I assume there must be some similar reason.

Dave
Los Angeles, CA
-Rail Radio Online-Home of the "TrainTenna" RR Monitoring Antenna-
http://eje.railfan.net/railradioonline

[Overmod]

You can work out the differences for yourself; think about 'em a bit.

Piggyback involves trailers being transported on flatcars. The flatcars can be specially designed for light weight, or to drop the trailer wheels as low as possible to keep the center of mass low, but no part of the trailer either contacts the track or takes any of the train's buff or draft force.

With RoadRailers, the trailers *become* the train. Early ones had an integrated set of railroad wheels at the back, similar to the wheels on a hy-rail truck. Much of the actual weight of the trailer was carried by the inner set of rubber tires, which simplified the suspension of the rail adapter. The later RoadRailers use a relatively conventional four-wheel freight truck articulated between trailers. Lower overall tare weight, and no need to have as many flatcars as you have trailers. But if your trailer isn't equipped to ride the rails, you're SOL.

Loading and unloading pigs is interesting, particularly onto the skeleton-flat kind of car.

Note that containers are a separate type of operation. A container is like a very heavy trailer body without the wheels, with special fittings at the corners with which it can be lifted and moved. This permits the use of very light and skeletal 'spine cars' to keep tare weight low... or easy double-stacking (DON'T try this trick with piggybacking!!!) with heavier cars. It is also theoretically easier to keep containers secured to the flatcar than trailers... you have four locking corner clamps vs. something like a raisable fifth wheel for the kingpin and chains or locks for the rear of the trailer. However, if you don't have an appropriate underframe (like a flatbed truck or trailer chassis without the decking) your container can't be driven anywhere. A piggyback is ready to be driven off about as quickly as it can be taken off its car and put where a tractor can reach it...

You didn't mention RailRunners, the topic of a recent thread here. These rather naturally combine the 'advantages' of separable containers and RoadRailers. It will be interesting to see whether this design addresses many of the potential problems and opportunities such a mode will have...

[Anonymous]

QUOTE: Originally posted by M.W. Hemphill

BNSF is now accepting ordinary trailers in straddle-lift piggyback service -- it used to be that only special reinforced trailers (Z trailers) could stand the abuse of a straddle-lift. This is one of the more significant technological breakthroughs in recent years, and it's hardly been reported. I didn't even know about it until this spring. I don't know if the technology is available to other railroads or if this is a BNSF-only.

Regarding this potential bombshell of innovation, is BNSF accepting any trailer, e.g. tankers, flatbeds, as well as dry vans? If so, they have just tapped a huge market. My understanding is that over 70% of the trailers out there are not the reinforced Z trailers, and the prevailing thought was that such trailers could only piggyback using roll-on/roll-off platforms, which would require more capital investment for an untested marketing concept. In fact, didn't railcar maker Trinity just come out with a new 7 platform articulated ro-ro car? If BNSF has found a cheaper way to carry non-reinforced trailers on standard TOFC cars, then they have scored a big one!

Dave