Why semi-trucks are called like that? What is so “semi” about them?

Why semi-trucks are called like that? What is so “semi” about them?

We use words without paying much attention to them. For example, words “semi-truck” are used commonly, but how many people know what that means? What is “semi” about these machines? There are actually two possible explanations.

In US and some other countries semi-trucks are simply referred to as Semi’s. It is a name everyone understands and once you mention a semi-truck everyone has an image in their heads of an articulated vehicle, consisting of a tractor unit and a trailer. Actually, the trailer is part of the story why semi-trucks are called like that.

Semi-trucks are, most of the time, hauling semi-trailers. A simple trailer is a wheeled platform, which can stand on its own on its wheels without any support. Meanwhile semi-trailers only have wheels at one end of the platform. The other end relies on the chassis of the semi-truck for support when driving. It cannot stand by itself on its wheels – it needs extendable legs or some other type of support structure. Semi-trailers cannot be hauled by anything else – they need an appropriate semi-truck to move. Even if you took the most powerful agricultural tractor, you could not safely pull a semi-trailer, because the front of it doesn’t have wheels and needs a chassis to rest on when travelling.

Semi-trucks consist of a tractor unit and a semi-trailer. Image credit: PRA via Wikimedia(CC BY 2.5)

But that is just a part of the explanation. Semi-truck is a combination of a semi-trailer and a tractor unit. Not that difficult to understand and it totally makes sense. But there is another explanation for where did this name come from.

The hitch mechanism at the back of the semi-truck is commonly called a “fifth wheel”. There are two most common types of fifth-wheels: semi-oscillating and fully-oscillating. Most semi-trucks feature a semi-oscillating hitch (turntable hitch or fifth wheel – whatever you want to call it). It means that the hitch mechanism is not entirely rigid – it tilts slightly from front to back. Imagine that the rear of the semi-trailer gets a little bouncy and starts moving up and down. The fifth-wheel will accommodate that movement, making the entire truck more stable. But if the trailer is tilting sideways, the semi-oscillating hitch will not move with it – a semi-oscillating hitch does not tilt from side to side. It is not usually a problem, though, because semi-trailers typically have enough flexibility in their chassis to absorb lateral movement without disturbing the balance of the tractor unit.

Logging trucks sometimes use fully-oscillating hitches. Image credit: ChattOconeeNF via Wikimedia(CC BY 2.0)

However, in some situations a fully-oscillating hitch has to be used. For example, in forestry semi-trucks. Because the terrain is so uneven, semi-trailers get rocked quite a lot. A fully-oscillating hitch tilts from side to side and thus allows for more movement in the trailer without disturbing the truck. This is also beneficial when the semi-trailer is very rigid (for example, when it is a tanker). However, fully-oscillating fifth-wheels are more complex, more expensive and typically unnecessary, which makes them pretty rare. That could be why semi-truck name stuck.

The reason why semi-trucks are called this name is probably combination of both of these theories. You should remember that a typical semi-truck is an articulated vehicle, consisting of a tractor unit and a semi-trailer, connected through a semi-oscillating hitch.

Renault will begin selling electric trucks in 2019 – it is going to be an exciting year!

Renault will begin selling electric trucks in 2019 – it is going to be an exciting year!

Truck electrification is beginning to reach its stride. Companies are in some sort of a race, which will result in a lot of new electric trucks being introduced next year. You‘ve heard of Tesla Semi, Cummins Aeos, Daimler and maybe even Volvo‘s plans to introduce new electric trucks in 2019. And now Renault is joining the crowd.

It would be easy to think that Tesla started this trend with its Semi – a super fast and efficient semi-truck, which can reach 97 km/h in just 20 seconds while pulling a heavy load. However, this impressive machine was not the first electric truck to be announced. For example, Daimler has been experimenting with electric technology in its trucks for quite some time already. The main focus of Daimler is different than the one Tesla. Daimler is looking forward to introduce electric urban delivery trucks, which are smaller and typically travel smaller distances every day. Cummins had a similar idea when it introduced its Aeos – a day cab semi-truck with a range of around 160 km.

It seems that this trend is here to stay. Numerous manufacturers proved that electric heavy duty trucks are actually possible. Furthermore, they can be relatively affordable and easy to live with. If everything works as expected, Tesla Semi might actually be one of the most reliable semi-trucks in the market. Meanwhile big current manufacturers were not so vocal about their plans to start production of electric trucks.

Tesla Semi is probably the single favourite electric truck in general population. (Tesla’s picture)

Have you heard about electric trucks from Scania, MAN, Peterbilt and other giants of the truck industry? No. While there are certainly some plans, they are not developed to the stage of Tesla Semi or Cummins Aeos or even Nikola One. This new segment is up for grabs for the new players. However, some interesting projects are already coming from the well-known truck manufacturers.

Volvo Trucks has announced that it will introduce an electric urban distribution truck in 2019. While long haul machines are certainly in the plans, Volvo believes that city operations is where the electric trucks could thrive. In fact, Volvo said that electric urban distribution trucks could even work at night, helping to reduce city noise and congestion. And now finally we heard from Renault.

Cummins is a famous manufacturer of heavy-duty engines, but its Cummins Aeos truck is going to be one of the first urban delivery semi-trucks on the market (Cummins’ picture)

Renault Trucks has just announced that it will launch a new electric truck range in 2019. Pretty much at the same time when many other companies are going to introduce their first electric trucks – it is going to be an interesting year. However, Renault is not just following current trends. This company has been experimenting with electric technology since 2009, so it is about time to introduce some products into the market. For now the range will consist of urban and peri-urban delivery trucks. They are unlikely to feature such an extreme design like Tesla Semi or Nikola One. The reason is that smaller trucks do not have such big cabins, so there is not much room for extravagant design opportunities. However, we do expect some rounded corners, lack of big grill and some interesting paint schemes.

Renault has been experimenting with electric trucks since 2009 (picture of Renault Trucks)

So let’s see what we have. Daimler is preparing electric urban delivery trucks for intercity operations, Volvo is focusing on urban delivery and Renault is going to do a little bit of both. None of the major truck manufacturers in this article are preparing big semi-trucks, not even with day cabs. What does that mean?

It simply means that the old, trusted brands are letting new players to take on this market segment. They can jump on-board at any point they want, but for now they will just sit back and look how new manufacturers are going to do. Who knows, maybe smaller urban delivery trucks is actually a smarter step to this new age of electric trucking.

Why semi-trucks in US and Europe are so different?

Why semi-trucks in US and Europe are so different?

American and European semi-trucks are very different. You don‘t have to be a truck enthusiast or have brilliant understanding of the mechanical part of these machines to see that semi-trucks used in USA and Europe look very different. But why? Why different ideas about what the truck should look like prevailed in different places in the world?

The main difference you see is the overall design of the tractor unit. In Europe we usually see cab-over trucks. This means that the cabin is situated above the engine. This allows creating flat front surface and the entire truck with its trailer has a cuboid shape.

Meanwhile trucks used in US, Australia and in many other places in the world feature something called “conventional cab” design. This means that the cabin is behind the engine. Drivers are sitting further away from the actual front of the truck and look over the long engine cover when driving. So why in different places in the world different designs prevailed?

One of the differences between European and American trucking is that owners-operators are very common in US and not so much in Europe. These people own their own trucks and pretty much live in them for months at a time. Semi-trucks with conventional cabs feature longer wheel base, which makes them a little more comfortable. Also, they tend to have a lot of room inside. Owners modify their trucks to include huge living compartments – something not common in Europe. Without the engine under the cabin, getting in and out of the truck is actually easier, because the cabin is a little lower.

This is what conventional cab trucks look like – these are much more common in US, Australia and elsewhere outside Europe. (First Response Team of America, Wikimedia(CC BY-SA 3.0)

Another advantage of a conventional cab design is that the truck can be more economical. Surely they usually pull heavier loads, but if there were two trucks, one a cab-over and another one a conventional cab design, and they had the same powertrain and the same cargo, the conventional cab truck would most likely use less fuel. Of course, that is just in theory – in reality there are too many factors to consider.

Finally, engine in conventional cab trucks is easier to maintain and fix because it is very easy to reach. However, cab-over trucks do have their own advantages.

Cab-over trucks are simply more compact and easier to navigate through tight city traffic. (Volvo Trucks)

Square shape of the cab-over truck means that it is easier to place the truck close to other vehicles or objects. European semi-trucks are also lighter and have a shorter wheel bases, which makes them significantly easier to manoeuvre. Essentially, they are more compact and easier to work with in traffic and urban environments. But what are other reasons why different truck designs prevailed in US and Europe?

This is what the interior of a modern semi-truck looks like:


Why European and American trucks are so different?

Maximum length of a truck with a semi-trailer in Europe is 18.75 meters. Some countries have some exceptions, but generally that is the rule. In order to use the maximum of this length for the cargo the tractor unit has to be as short as possible. The best way to achieve that is to mount the cabin over the engine.

Similar requirements in US have been revoked back in 1986 and trucks now can be much longer. Actually, back in the day cab-over trucks were quite popular in US, but without strict limitations roomier and more convenient to live with conventional design trucks prevailed. The number of cab-over trucks in US is constantly declining.

Trucks of owners-operators typically have big living compartments. Meanwhile in Europe space is at a premium. (Pierre André, Wikimedia)

Another reason is speed. In Europe Semi-trucks are limited to 90 km/h, but in some places in US trucks reach 129 and even 137 km/h. That is where better aerodynamics and longer wheel base help a lot.

Finally, roads in US and Europe are very different as well. Cities in US have wide streets and interstate highways are very straight and wide. In Europe trucks have to deal with narrow streets, winding country roads and cramped parking spaces. Lack of space limitations allowed Australia to use conventional cab trucks too. That is also why Australian highways feature well-known road trains – extremely long distances and straight roads allow semi-trucks to pull up to four trailers.

Interested in trucks?

Volvo thinks electric trucks will help fighting traffic jams;

Electric trucks from a 100 years ago;

Gas-powered trucks are already available and in theory can be CO2 neutral;

Scammel Scarab – it is not your ordinary semi-truck – it is the mechanical horse;

General Motors Bison – a vision of trucks of the future from 1964. Why didn’t it stick?

Volvo says that electric trucks will not only be eco-friendly, but will also help fighting traffic jams

Volvo says that electric trucks will not only be eco-friendly, but will also help fighting traffic jams

The future of transportation is in the hands of electric trucks. They will be fast, they will be powerful and they will be efficient. And they will be here next year. Tesla Semi should reach its buyers sometime in 2019. Cummins and Daimler are both preparing electric trucks of different category to enter the market next year and now Volvo is saying it has something in its sleeve too. And it should reduce traffic jams.

How can an electric truck – literally just another vehicle on the street – help fighting congestion in city centres? Volvo Trucks reminds us that many cities now have strict regulation against noise pollution. This means that trucks have to operate during the busiest hours of the day. And that is a problem.

According to Volvo that because electric trucks will be much quieter, they will be able to roam streets at late evenings and at night. This will reduce the number of delivery trucks on the street during rush hours. Electric trucks will also be able to reach areas where conventional diesel trucks are simply not allowed to go due to noise and pollution regulations.

A study, conducted in Stockholm city, revealed that trucks operating off peak traffic hours managed to cut the delivery time by 66 %. These trucks can also be slightly bigger, since they will not have to navigate the daily rush hour traffic. A simple delivery truck can carry ten times as much cargo as the vans commonly used today. This means less trips and more effective utilization of road network.

We still haven’t seen how Volvo’s electric trucks will look like, but the first step will be urban delivery.(Volvo Trucks)

People who live in the city will benefit too from reduction of noise and cleaner air. World Health Organization estimates that by 2030 more than 60 % of world’s population will live in urban areas. In just 12 years from now cities of the world will grow by a billion people. This will cause increase in traffic problems, which are already pretty bad. It is estimated that in EU alone congestion and related traffic problems cost about a 100 billion euros per year.

Therefore, Volvo is going to start selling urban distribution trucks in Europe next year. However, initial testing with selected reference customers is already going to start this year.

Jonas Odermalm, Head of product strategy medium duty vehicles at Volvo Trucks, said: “Our technology and knowhow within electromobility are based on proven commercial solutions already in use on Volvo’s electric buses, and solutions that were introduced in Volvo’s hybrid trucks as far back as 2010. The vehicles themselves are only one part of what is needed for large-scale electrification to succeed. Enabling long term sustainable transport is a complex issue that requires a holistic and wide range of measures”. Issues regarding infrastructure are going to be discussed with cities and customers, in order to prepare the network for sustainable electric truck operations.

Also read:

Electric trucks from a 100 years ago;

Gas-powered trucks are already available and in theory can be CO2 neutral;

Scammel Scarab – it is not your ordinary semi-truck – it is the mechanical horse;

General Motors Bison – a vision of trucks of the future from 1964. Why didn’t it stick?

How a truck with a combustion engine can be CO2 neutral? (Video)

How a truck with a combustion engine can be CO2 neutral? (Video)

The world is moving towards electric vehicles. Electric cars are not even drawing attention in the streets anymore, and now several companies are pushing for electric trucks too. They will be silent, cheap to run and yet very expensive. But are there any other green alternatives? Old-school truck manufacturers are already offering CO2 neutral solutions that are ready to go right here, right now.

Gas-powered trucks are not a new thing. However, with improvements in infrastructure several companies are introducing new models, marketing them as a more approachable way to eco-friendly trucking. For example, Volvo introduced new FH LNG and Volvo FM LNG models that can run using biogas and liquefied natural gas. Interestingly, in terms of technology these trucks do not follow the path of older gas-powered trucks.

Volvo’s LNG engine does not use the OTTO cycle – the conventional diesel engine cycle allows keeping the same performance. (Volvo Trucks)

While most of gas-powered trucks use OTTO cycle, Volvo opted to stay with the usual diesel engine configuration. This allowed maintaining power and torque – 460 HP engine, producing 2300 Nm, makes the same figures in diesel-powered trucks. However, LNG trucks are much MUCH cleaner.

Filling up gap-powered trucks is relatively quick and you can cover a 1000 km on full tanks. (Volvo Trucks)

Volvo says that its LNG trucks will emit at least 20 % less CO2 to the atmosphere. However, this percentage in some way can go up to a 100, if the biogas is used. In that case trucks still do emit CO2, but it is essentially neutral in a way, because that CO2 was absorbed before producing the gas. In other words, no new CO2 is introduced to the environment. But Volvo is not the only manufacturer that had this idea.

Video about Volvo’s LNG trucks:


Scania introduced its new gas-powered truck engine virtually at the same time as Volvo. However, the 12.7 litre engine, called OC13, is using the OTTO cycle, which makes it extremely reliable. It is a little less powerful – makes 410 HP and 2000 Nm of torque. However, servicing is done less frequently and it can run on both LNG and CNG. Scania says that it emits at least 15 % less CO2 that diesel equivalents, but the impact on the environment is mostly decided by what type of gas is used. Biogas is virtually clean, considering the complete cycle.

Meanwhile Scania’s OC13 does use the OTTO cycle, but that translates into less frequent servicing and a more robust engine. (Scania)

Both of these engines will allow trucks to cover more than a 1000 km on full tanks – none of the electric trucks are promising such range on a single charge. Ant they are cheaper, and they are available now.

Finally, gas-powered trucks are much quieter than diesel counterparts, which is important because some urban areas already have some strict noise polution regulations. Gas-powered trucks may not replace electric trucks, but it is always good to have alternatives until electric powertrains become industry standard.

More reads about trucks:

Refuse handling and cleaning runways – two interesting applications for autonomous technologies;

How does a 100 year old electric truck look like?

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