Driving up to Flagstaff this weekend we noticed several trains with maybe 80-100 cars double stacked with containers. Obviously the total weight of these trains is staggering.
Anyone know if there is an legal/upper limit of the number of cars one train can pull? How about an legal/upper limit on the weight than can be pulled. Lastly, any estimates of the amount of time or total distance it would take for one of these trains to roll to a stop from 20 MPH on a flat surface?
No legal limit of length that I know of (I understand Class I railroads have tested 2+ mile long freights), and the former physical limit of coupler strength (i.e. how many freight cars you can pull before the coupling between cars fails) can be gotten around by having distributed/remote power units - a fancy name for remote-controlled locomotives cut into the middle of the train, to ease the strain on the couplers.
As for weight limits, there are physical limits that track is rated for - most track can now handle 286,000 lbs cars, some track has been upgraded to handle 310Klbs frieght cars - the previous standard was 263Klbs. I know there have been 125ton freight cars (the load limit, not the weight of the car itself) for awhile now, not sure if 130tons or greater are out there in force.
And the braking distances are pretty darn long, IIRC assume a mile or more at moderate speeds.
BTW, Intermodal trains (those containers trains you saw) are not necessarily all that relatively heavy compared to unit trains of 110t coal or ore freight cars, so keep that in mind…
If there are legal restrictions on length are they justified by the physical limitations of the equipment or by how much time it would take to clear a crossing? The couplings may be able to tolerate a two mile train but I don’t think your average commuter would.
There used to be practical limits on the length of freight trains because of the amount of force exerted on the couplers. Just like the old high-school physics demonstration with the blocks hanging from strings, the couplers in the front of the train have to handle the entire weight of the train while accelerating. Distributed power, which is a relatively new technology, allows the addition of remote controlled locomotives in the middle or at the end of a train, which can allow much longer trains. Another limiting factor was the delayed and reduced braking effectiveness near the end of the train with conventional airbrakes, which has been addressed with electronic controlled airbrakes.
The limit has recently been 12,000 feet (about 2.3 miles or 3,658 meters) for trains with electronically-controlled brakes. I’m not sure if this limit is (or was) legally enshrined or just the position of the AAR. Some of the big rail roads have been running some experimental “monster trains”, such as this 3 and a 1/2 mile long one, but I don’t know if any are regularly running them yet or not.
The additional locomotives are controlled remotely from the cab in front, so they don’t require additional crew.
Also, from a logistical (traffic management) standpoint, a 2-mile long train is still just one train that needs to be scheduled and routed. Two 1-mile long trains would need to be scheduled and managed as 2 trains, with adequate distance between them so they don’t run into each other.
Also two trains take up two signal blocks, whereas one big train only uses one. A signal block is (to hugely simplify) the track between two signals which only one train is allowed to occupy at a time. It doesn’t matter if it’s a 2 mile long coal train or a small service vehicle. Obviously it becomes an issue if the trains are so long they’re taking up multiple signal blocks, but otherwise a typical rail network will be able to handle a lot more cargo with fewer long trains than more short ones.
If a super-long train is run with no additional crew, what happens if there is a problem (or suspected problem) with the train? It would take a crew member nearly two hours to walk to the back of the train and return to the front in order to inspect the train (plus time to actually deal with the problem).
I guess you didn’t look at the picture. It was a mixed manifest train. Discussions of it on an Illinois railfan listserv suggest that it wasn’t that unusual, that trains over two miles long are now fairly common in the Midwest and Prairie Provinces.
As for checking a problem, I’m not sure why it would take someone walking four mph more than a half hour to walk to the back of a two-mile-long train. In practice, the conductor would usually just step down at a grade crossing or similar location, then have the engineer pull the train slowly forward until the suspected trouble spot was adjacent.
One 2-mile train also disrupts less traffic at crossings. While it takes longer for the train to pass you will still have a fixed amount of time to wait before and after the train reaches the crossing. With 2 1-miles trains you have twice that.
Another limiting factor to overall train length is the length of sidings along the route…the “pullouts” where two trains can pass. Obviously a siding has to be long enough to accomodate an entire train*. I believe the standard length for passing sidings is generally about 8000 ft. or just over 1-1/2 miles although some railroads are now building 13,000 ft. sidings.
The total weight of a train is not much of a factor in determining length. The effect of weight on track, bridges etc. is determined by axle loadings…the amount of weight on each set of wheels. As long as each individual railcar is not loaded over capacity, the weight of the entire train is mostly irrelevent insofar as infrastructure is concerned
*There actually is a process known as a “saw-by” by which two over-length trains can pass on a short siding, but it is usually avoided as it is tedious & time-consuming involving a lot of backing & filling, uncoupling and re-coupling cars, etc.
Not too sure if mile+ long freight are normally travelling at 55mph on the main - may be more like 40mph except for intermodals or refrigerated product unit trains.
As for how long it would take without application of brake (coast to a stop) - I dunno, you’ll need to test that yourself on the Trans Austrailan Railway
(Actually the FRA railroad testing facility at Pueblo probably has done ‘coasting to a stop’ tests, but with little track friction and good roller bearing on the axles it will be a long distance).
Another very general rule of thumb I’ve heard is that a train takes its own length to stop. Neither rule is particularly dependable as there are so many variables. Speed, track condition, type of equipment, operator’s course of action/reaction time, etc. Train brakes have a “full emergency stop” function…the equivalent of locking up the brakes on an automobile… but as with autos, it is rarely used as it can have some very bad effects. On an automobile it can send the car into an uncontrolled skid, with a train an emergency application can result in derailment and/or damage to equipment and track. And it still doesn’t stop right away.
Another thing to consider is that train brakes are controlled by a pressurized air line running the length of a train. It can take 15 seconds or more from the time the brakes are applied at the head end of a train until the pressure change is felt at the rear and all brakes begin to take hold. Electro-pneumatic braking is currently being experimented with and promises much faster application times, but it is likely to be many years before it can be applied to the tens of thousands of pieces of rail equipment out there.
I was a conductor and yardmaster for Norfolk Southern. For my particular area we weren’t allowed to build trains bigger than 150 cars but that was an unofficial rule.
There are areas where making them too long would block road crossing for too long.
As far as weight, we had a section in our rule books which dealt with grades over a particular area and how much horsepower you’d need to pull over that railroad. A rule of thumb as a yardmaster was to use a 1 to 1 ratio when making up a train. So 4000 tons would require One 4000 horsepower engine, 12000 tons 3 engines.
We operated over CSX railroad & I remember a 200 car train (one of theirs) broken into 4 separate sections…all knuckles breaking. That big of a train is going up and down hills at the same time, plus it was a mixed freight train which usually has full & empty cars scattered all over the train.