# How many train passes can railway tracks endure?

I know that the rubber on car and truck tires wear, and the road concrete wears out. I wondered:

While steel is hard and elastic, it still causes friction (interaction between molecules) and therefore abrasion.

Let's say we have on average 20-30 wagons with four axles with a full load of 50-60 tons on each wagon and a traction vehicle. How many train passes can a railway rail endure before it must be replaced? What is the equivalent time frame in which this number of passes is achieved on average?

• I suspect the footing wears much faster than the steel. Are you asking specifically about the steel, or about any component of the track?
– Air
Apr 3, 2015 at 18:04
• Only the steel tracks Apr 3, 2015 at 18:16
• @Air -- footing wear is also dependent on whether you have wood, composite, steel, or concrete ties installed -- wood or composite ties are vulnerable to plate cutting and other such behavior that leads to early development of wide gauge, while steel and concrete don't do that Apr 7, 2015 at 1:06

This is an admittedly North American response.

MGT

In the US, how much traffic goes over a given track in a year is measured in Million Gross Tons (MGT) e.g. 1 MGT = 2 000 000 000 lbs [spaces instead of commas to be world-friendly]. This is a measure of the total weight of cargo and vehicles but not necessarily the number of individual trains.

Rail Life

The life of a typical railroad rail is between 1300 MGT and 380 MGT depending on if the rail is on a straight (tangent) track or in a curve. There is more friction in a curve. Also, the rail on the low side of a super-elevated curve wears faster than the rail on the high side.

Friction

Because of this great difference in life of the rail, areas that have lots of curves employ machines that add lubrication to the rail. This lubrication is applied after the locomotives pass so that their traction capability is not reduced. Some photos of these machines are below:

Number of Trains

In the US, the largest/heaviest trains carry only one commodity. A typical example of this is a so called "coal unit train". This is a 100-car train loaded with coal where each car weighs 286,000 lbs. Assuming an average of 500 MGT of life:

$$\text{Number of Trains} = \frac{500*1e6}{(100*\frac{286,000}{2000})} \approx 35 000 \text{ trains}$$

A high capacity line might have 25 trains a day on one track, so the life span in years would be:

$$\frac{35000}{25*365} \approx 4 \text{ years}$$

• Wow. If we take the smaller value (1 gross ton = 1.016 metric tons) and estimate that a train with the weight of 25 waggons goes hourly over the track then we have (380*1016*1000)/(25*60*24*365) = 30 years of continued usage. With the bigger value we have an estimated lifespan of 100 years ! Apr 3, 2015 at 21:42
• @ThorstenS. Yes, I was going to add that calculation to the answer, but the numbers seemed really high! I'll look at it more and add those numbers.
– hazzey
Apr 3, 2015 at 22:05
• @hazzey: Are the numbers you quoted for continuous welded track or the older style track that had thermal expansion gaps between rail segments? Continuous welded track offers less friction, a smoother ride, suffers less damage because of its uniform surface, compared to the older style track & is less damaging to the wheels on trains.
– Fred
Apr 3, 2015 at 23:03
• @Fred Those life numbers should be for continuously welded rail (CWR).
– hazzey
Apr 7, 2015 at 2:35
• Surely a million gross tons is 2 240lbs x 1 000 = 2 240 000 000 lbs. Or is the intended meaning "Millions of Tons Gross"? Oct 11, 2016 at 14:28