The heaviest trains in the world are freight trains hauling bulk commodities such as coal and iron ore. The weight of trains generally does not include the weight of the operating locomotives; this is not considered dead weight, so is not included. If for example a train had two locomotives operating and was simply hauling a third off line, this third locomotive would be included in the payload weight.
If the track and its alignment are strong, gauge is not so important. Among railways with over 20,000 t (19,684 long tons; 22,046 short tons) gross train weight, the Sishen–Saldanha railway line uses 1,067 mm (3 ft 6 in), while the others use 1,435 mm (4 ft 8 1⁄2 in) standard gauge.
Most Pilbara region railways operate on pre-stressed 68 kg/m (137 lb/yd) rail, meaning that each metre of track weighs 68 kg or each yard of track weighs 137 pounds. This gives the track the strength to carry such heavy loads.
1.2. Axle Load
The highest permitted weight per axle is:
- 2008 – Fortescue – 42 t (41 long tons; 46 short tons)
- 1830 – Stephenson's Rocket 2.2 t (2.17 long tons; 2.43 short tons)
The track bed and the strength of the rails themselves limit the axle load.
1.3. Line Load
Line load is the weight per metre or foot of train length. The strength of bridges is what mainly limits this. Examples:
- 12 tonnes per metre (3.60 long ton/ft; 4.03 short ton/ft) (Iron Ore Line, Sweden)
Curves must not be too sharp; wagons may be pulled off the track and derailed, especially with general freight trains where light and heavy wagons are intermixed, less so if all cars in a train are loaded and unloaded at the same place and equally much. The meaning of "too sharp" depends as much on experience as on a specific formula.
The couplers must be strong enough in heavy trains. Janney couplers are used for the heaviest trains. The SA3 couplers handle trains of 6,000–8,000 tonnes (5,910–7,870 long tons; 6,610–8,820 short tons), as Russian trains limited by loop lengths, etc.; maximum load of SA3 couplers have not been tested. The standard buffers and chain couplers used in Europe can only handle 3,000–4,000 tonnes (2,950–3,940 long tons; 3,310–4,410 short tons) train weight, but trials are made to push this limit to 5,400 tonnes (5,310 long tons; 5,950 short tons).
- Fortescue – 40,000 t (39,400 long tons; 44,100 short tons) gross train weight, 2,700 m (3,000 yd) long
- Glencore 9,000 t (8,900 long tons; 9,900 short tons) (load) 1,500 m (1,600 yd) long.
- Aurizon: 1,435 mm (4 ft 8 1⁄2 in) standard gauge bulk iron ore train to Esperance, 11,000 t (10,800 long tons; 12,100 short tons) (load); 14,500 t (14,300 long tons; 16,000 short tons) (gross) 1,435 mm (4 ft 8 1⁄2 in) 32,320 t (31,810 long tons; 35,630 short tons) (gross weight excluding diesel locomotives) 40 t or 39 long tons or 44 short tons axleload)
- SCT Logistics; 1,435 mm (4 ft 8 1⁄2 in) freighter from Parkes to Perth, June 2008, 6,000 t (5,900 long tons; 6,600 short tons) and 1,800 m (2,000 yd) with diesel locomotives / (crossing loops are 1,800 m or 2,000 yd)
- BHP: 1,435 mm (4 ft 8 1⁄2 in) June 2001 trial with 682 ore cars and eight distributed GE AC6000CW locomotives with a total weight of 99,734 t (98,159 long tons; 109,938 short tons).
- BHP 39,680 tonnes (39,050 long tons; 43,740 short tons) 
- One Rail Australia 1,435 mm (4 ft 8 1⁄2 in) bulk iron ore train to Whyalla - 82 wagons and 1,752 metres (1,916 yd) long, 12,254 t (12,060 long tons; 13,508 short tons)
- Arrium 1,435 mm (4 ft 8 1⁄2 in) - 13,000 tonnes (12,800 long tons; 14,300 short tons) (4 locos, 160 wagons) - heaviest on national network.
- Carajás railroad, 1,600 mm (5 ft 3 in), Iron Ore typically 330-car trains, each 3 km (1.9 mi) long.
1,435 mm (4 ft 8 1⁄2 in)
- Bulk trains are limited to 3,000 m (9,800 ft) length with up to 20,700 tonnes (20,400 long tons; 22,800 short tons)
- Iron ore trains on Quebec North Shore & Labrador Railway 33,000 short tons (30,000 t; 29,000 long tons)
- Daqin: 1,435 mm (4 ft 8 1⁄2 in) standard gauge coal trains – 20,000 tonnes (19,700 long tons; 22,000 short tons), 3,200 m (3,500 yd), 210 wagons
- SNCF: 947 m long freight train with 67 wagons – 5,410 tonnes (5,320 long tons; 5,960 short tons). Train was composed of two coupled ordinary freight trains using standard buffers and chain couplers. Therefore, the locomotive of the second train became a mid-train helper, but was still manually operated. The first train consisted of two locomotives BB 27000 with 44 flat cars loaded with steel plates; the second train consisted of one BB 27000 with 23 coal hoppers. The train ran in the night from 28 to 29 October from Somain to Woippy and reached a maximum speed of 100 km/h (62 mph). More tests on the same route are planned for spring 2016. The regular service will start in December 2017, with remote controlled mid-train helpers.
2.6. Germany / Netherlands
- Rotterdam-Dillingen iron ore trains - 6,000 t (5,900 long tons; 6,600 short tons)
- Proposed – Kalia iron ore – 20,000 t (19,684 long tons; 22,046 short tons) – 1,435 mm (4 ft 8 1⁄2 in) standard gauge – iron ore
The heaviest trains length is 750m and weighing 4,000 tons.
And a recorded 12,000 tons train in 1993 with 100 six axle iron ore cars pulled by 6 GT26CW locomotives in three positions, Front, middle and at the end connected by locotrol.
- Existing – 800 t (790 long tons; 880 short tons) – 1,000 mm (3 ft 3 3⁄8 in) metre gauge
- Proposed – 4,000 t (3,940 long tons; 4,410 short tons) – 1,435 mm (4 ft 8 1⁄2 in)
- Improvement due to heavier 60 kg/m (121 lb/yd) rail, gentler curves and gradients.
- Mauritania Railway - 20,000 t (19,700 long tons; 22,000 short tons) 1,435 mm (4 ft 8 1⁄2 in) – iron ore
2.11. Russia / Finland
- The longest and heaviest freight train ran as a test train on February 20, 1986, from Ekibastuz to the Urals was carried out with a coal train. The composition consisted of 439 wagons and several diesel locomotives distributed along the train. The mass was 43,400 tonnes (42,700 long tons; 47,800 short tons) and the total length of 6.5 kilometres (4.0 mi).
- Chita - Zabaykalsk (break of gauge at Chinese border) up from 4,000 to 6,300 tonnes (3,940 to 6,200 long tons; 4,410 to 6,940 short tons). Russia uses special SA3 couplers allowing higher weight than in most of Europe.
- In 2014 Russian Railways presented a new locomotive called 4ES5K adopted for 7,100-tonne (6,990-long-ton; 7,830-short-ton) trains to be put into operation in 2015.
- The heaviest trains in Finland weigh approximately 5,400 tonnes (5,310 long tons; 5,950 short tons) and carry iron ore pellets (taconite) from the mines and processing plant in Kostomuksha, Russia . They go from Kostomuksha to Oulu, Finland, as 60-car unit trains measuring approximately 880 metres (2,890 ft) in length. In Finland these trains are hauled by two Sr2 class electric locomotives at 25 kV 50 Hz AC while in Russia trains are hauled by double-section 2TE116 class diesel engines. Due to the restrictions caused by passing loop lengths between Oulu and the port of Kokkola the trains are shortened to 30-40 cars in Oulu and are usually operated with Sr1 class electric locomotives for the rest of the way. The trains use exclusively Russian rolling stock and are equipped with SA3 couplers.
2.12. Saudi Arabia
- Freight trains on the new North-South will carry 15,000 t (14,800 long tons; 16,500 short tons) and be 100 wagons long. Later estimates are for 15,000 t (14,800 long tons; 16,500 short tons) and 155 wagons.
2.13. Sierra Leone
Sierra Leone had a 762 mm (2 ft 6 in) narrow gauge railway with 5 t axleloads. Train loads were necessarily very limited, which increased costs counter-productively, as large numbers of small trains were needed to haul tonnages that heavier railways could haul with fewer trains. For example, in 1956 fourteen modern 4-8-2+2-8-4 Garratts were purchased from Beyer, Peacock & Company. These locos increased the maximum load over 1:50 grades from 200 tons (203 tonnes) to 270 tons (274 tonnes).
2.14. South Africa
- Sishen–Saldanha railway line: 41,400 t (40,700 long tons; 45,600 short tons). (Gross weight) 3,875 m (4,238 yd) long, 9 locomotives in 4 sets remote distributed power management (342 cars with 100 t (98 long tons; 110 short tons) ore each)  Uses 50 kV AC.
- Manganese: 16,640 t (16,380 long tons; 18,340 short tons) 
2.15. Sweden / Norway
- On the Iron Ore Line which goes between Luleå, Sweden and Narvik, Norway, iron ore trains are hauled by 360 t (350 long tons; 400 short tons) IORE locomotives. These 8,660 t (8,520 long tons; 9,550 short tons) trains (incl locomotive) are the heaviest in Europe. Special SA3 couplers, and 15 kV 16 2⁄3 Hz electrification are used. The iron trains go either Kiruna-Narvik or Gällivare-Luleå. Other very heavy trains go in flat areas but these trains go through a mountain range in Arctic climate, although the uphill grades are at most 10 ‰ (1 %) in the direction with loaded trains. Other heavy trains in Sweden are no more than 3,500 t (3,400 long tons; 3,900 short tons) limited by buffers and chain couplers.
The axle load on Malmbanan is 30 Tonnes and trials are underway to increase the axle load to 32,5 Tonnes. Axle load is called STAX in Sweden so the railroad is planned to go from STAX 30 to STAX 32.5.
- 3,250 t (3,200 long tons; 3,580 short tons) – electric hauled
2.17. United States
- Many main routes in the western US allow cars with gross weights up to 315,000 lb (142,882 kg) (157.5 short tons or 140.62 long tons or 142.88 tonnes).
- A Duluth, Missabe & Iron Range ore train pulled by a single 2-8-8-4 "Yellowstone" steam locomotive which totaled over 19,000 short tons (17,000 long tons; 17,200 t)
- A BNSF train from Ogden, Utah, to Roseville, California, was 14,000 short tons (12,500 long tons; 12,700 t)
2.18. World Record
The world heaviest train record is registered as follows:
Australia, BHP: 2001, trial with 682 ore cars and eight distributed GE AC6000CW locomotives with a total weight of 99,734 t (98,159 tons)
South Africa, Sishen Saldanha: 1989, 660 fully laden ore trucks, nine electric locomotives, seven Diesel engines and three other cars with a total weight of 70,543 tons made the journey, taking 12 minutes to pass by the watching engineers.