How many cars can a freight train have?

Question

How many cars can a freight train have?

Answer 1

Actually, there are limits as to how many cars a train can consist of, but not for the most obvious reasons.

More often than not, people tend to think of trains in terms of tonnage, power, coupler and draft gear limitations,, etc.  The limitations are not found here, directly, but rather in terms of length.

Length is crucial to the air brake system, for a number of reasons.

The brakes operate with air pressure.  When they are applied, they do so not by sending air into the brake system, but by exhausting air out of the system.  (I'll not go into detail here, but if someone asks, of course I'll try to answer).

In most instances, trains are operated from the lead locomotive with no engines within the train as "helpers" or "DPUs" (distributed power units.)  Though the remote DPUs assist in charging the system and making reductions, they are limited by how far the radio transmissions from the controlling locomotive can be received.  At one time the SP experimented with "repeater cars", but they failed to perform satisfactorily.

Length comes into play when the brake system needs to be charged with air from the lead engine consist.  For freight equipment, 90 psi is standard operating pressure.  The air pressure gradient increases the farther away it is from the charging source.  Typically, with the above operating scenario, at a length of 7500', one would expect to carry 90 psi an the head end with a resultant 84 or 85 psi on the last car when fully charged in decent weather, with a tight "brake pipe" (aka train line), with less than 5 psi per minute leakage.

The longer the train, singled headed, that greater the gradient, to a point where either insufficient air is maintained on the rear end or the brakes will operate unsatisfactorily.

Now, lets examine another parameter.  The rate of propagation is rounded off to 500' per second at a service rate of reduction.  Therefore, with a train of 8000', when the engineer applies the brakes, it would take 16 seconds for the air pressure to reduce on the last car.  Travelling 60 MPH, you have just covered 1/4 mile before the brakes even start to set up on the rear car.

When the brakes are released, the system needs to be recharged.  Here, the rate is 1 minute for every 12 cars in the train. 120 cars, ten mintues to reharge.  Again, at 60 MPH, you are going to be ten miles down the road before the brake system is fully recharged.  If the engineer needs to apply the brakes before the system is fully recharged, things become complicated.  Again, this info is an answer to another question.

There are other considerations for air brake operation that I will try to explain when the right question is asked.

Answer 2

Hoghead brought up several good points.  In our neck of the woods, trains are limited to 10000 feet as a rule, because that's the length of the longest siding - in other areas on our railroad, they can be 14000 feet long or more.  Also, there are mountains here, and if you have too many engines pulling too much weight up the grade, the simple weight of the train will tear itself apart, so you have to watch your tonnage around here.  We say that, in this area, there can only be 24 powered axles on the head end of the train, so if it's too heavy for 3 engines to pull, then it's time to drop some cars off or call for a helper on the tail end.  Some railroads used to add extra engines in the middle of the train, but I gather that this isn't done anymore.

Answer 3

The most I've seen is 130 without counting the three engines pulling them and one engine pushing them. But I don't think there's an actual set number.

Answer 4

The longest freight train I have ever seen was 166 cars, 14,000 tons, and 1.34 miles long. however before the BN/ATSF merger the BN used to run coal trains to Chicago that were 180 - 200 cars long and weighed nearly 30,000 tons. however after the merger they (both railroads) passed a law limiting coal trains to 128 - 135 cars long to prevent angry calls from trapped motorists.

Answer 5

It more about tonnage that it is number of cars...I have counted over 150 cars before which made the train over 1 1/2 miles long. That train was around 17 thousand tons or 34 million pounds.

Answer 6

there is no max. to how many cars a train can have in it.