Trains are amazing machines that have been used for more than a century to transport people and goods around the country.
They can pull thousands of tons of cargo in a single train, making them one of the world’s most efficient forms of transport. But how is this possible when trains are so heavy?
Here are 7 reasons why trains are so heavy.
1. To Improve Traction
Trains must be heavy to have sufficient traction between the steel wheels and the rail. The heaviest part of a train is the locomotive, which has the driving wheels.
If the locomotive is too light, the wheels will slip (spin) on the rail. This will cause heat to build up on the wheels, further reducing traction.
The locomotive is equipped with a sand dispensing system. This system blows sand onto the rail in front of the wheels to increase friction and overall traction. Steel wheels on a steel rail do not have traction unless there is sufficient weight bearing down on it.
The second reason for using steel wheels on trains is to reduce the rolling resistance. The contact patch of each steel wheel that contacts the rail (track) is about the size of a dime (19mm).
Keeping a heavy train moving on a flat surface (rail) at a constant speed takes no extra energy than keeping a light train moving. The energy loss is only noticeable when accelerating or climbing uphill.
The train’s steel wheels are heavy on their own, weighing around 750lb. (340kg). These wheels need to keep their shape while supporting immense weights.
The complete truck wheel assembly contains the suspension, propulsion, brakes, and wheels and can weigh over 20,000lb (9,700kg).
Summary
- Weight improves traction
- Steel wheels have a low rolling resistance
- Sand must be used to increase friction
- Not enough weight will cause the wheels to spin
2. To Improve Braking
The braking system on a train must be strong and robust, increasing the weight of the brake system. Trains use a pneumatic or vacuum brake mechanism similar to a car drum brake system.
They also use a dynamic brake which will turn the motors into generators and supply energy back into the grid or onboard systems.
The brakes on a train are usually very good at bringing the wheel to a stop, but this does not necessarily mean the train is also at a standstill (skidding).
The low rolling resistance of the wheels is not great for stopping a 10-thousand-ton train. So to counter this effect, the wheel trucks have suspension.
This will allow all the weight of the train to transfer into the rail, increasing the friction and bringing the train to a halt.
It usually takes more than a minute for a train to stop, so everything that helps speed up the brake speed will be used.
Summary
- Weight improves the effectiveness of the brakes
- Trains have two braking systems
- Low Rolling resistance increases the stopping distance
- Steel wheels can skid on the rail under heavy braking
3. Trains Are Heavy For Strength
Trains are designed to carry cargo and passengers from point A to point B. The only way to make a train cost-effective is to transport large quantities over long distances.
But trains can carry large and heavy items, so the train freight cars must be strong. A single freight car can weigh between 40 to 80 tons empty and can hold up to 100 tons (220,000.lbs) of cargo.
To hold so much weight, the freight cars are made from thick steel that can withstand the immense forces they will endure during transport. Passenger train cars can be made lighter and are often made from aluminum.
Summary
- Train freight cars carry up to 100 tons
- Thick steel construction for strength
- Heavy freight cars reduce carrying capacity
4. Large Engine And Generators
The locomotive houses the engine and generator. On a diesel-electric locomotive, the engine can weigh in at 11 tons and the generator an extra 4 tons.
Then there is the additional equipment, such as the head-end power unit, which supplies power to the rest of the train’s electrical system.
The diesel engine is large so that it can produce enough horsepower at a constant RPM. The Caterpillar EMD710 diesel engine is a V12 two-stroke with 710 cubic inches (11.6 liters) per cylinder for a total of 8,520 cubic inches (139.2 liters).
The large engine only produces 3,300 horsepower, but it will last for many decades.
Summary
- Large engine for durability
- The heavy weight helps with traction
- Not overly powerful
- Two-stroke engines burn more oil
5. To Withstand Shunting
The train cars need to be moved around when they are in the rail yard. This is called shunting or coupling.
To do this, the cars are lightly pushed against each other, coupling the cars together. But there is no easy or light way to push or bump 30 to 60-ton steel cars against each other at 5mph.
Shock absorbers are placed at the train’s front and back to absorb these forces. The shock absorbers can weigh over 440 pounds (200kg) each, adding to the weight of the train.
But the trains must be built strong enough to deal with these forces and carry heavy loads.
Summary
- Built heavy and strong
- Shock absorbers to assist with the shunting forces
- Shock absorbers are heavy and do not take the full force of shunting
- Adds weight to the freight car
6. To Increase Safety
The train cars can be built with extra structural supports and use stronger, heavier metals to improve safety.
Although newer passenger rail cars are built with crumple zones to absorb an accident’s impact, they are still heavy. The most important aspect is to keep the rail cars structurally sound in the event of an accident.
To prevent a 70-ton, 60-foot long, 12-foot high, and 8-foot wide tube from collapsing in an accident takes a lot of strength.
The strength will come from all the additional metal strengthening components used to build a rail car. The added strength characteristics also improve the life span of the rail car.
Summary
- Heavy rail cars are safe in an accident
- Built to last
- Strength is the primary safety feature
7. Trains Don’t Need To Be Light Weight
Trains do not need to be lightweight, as they have many design factors that work in their favor. They have sufficient power to propel them forward and perfectly designed wheels with low rolling resistance.
Being heavy will prevent the train from easily derailing as its center of gravity is low to the ground.
Trains need to be built strong to transport heavy loads and handle everyday wear and tear. Trains run on tracks, and the routes are extensively mapped out, so there is no need to stop suddenly.
Trains are designed to be heavy, and this makes them safer.
Summary
- Perfectly designed for their tasks
- Being heavy works in their favor
- Lightweight trains may be more efficient
