Why is an 18 wheeler truck called a 'semi'?

sequoianoir

Basically because it is articulated and comes in two bits. "an articulated truck consisting of a towing engine ("tractor" in the US), and a trailer that carries the freight." http://216.239.59.104/search?q=cache:zfyibX_HOT0J:en.wikipedia.org/wiki/Semi-trailer+18+Wheeler+Truck+called+a+Semi&hl=en&ie=UTF-8 Nov 19 03, 7:38 PM

robboy

I'd been told, by truckers, that it has nothing to do with the tractor; it's the trailer that is semi-wheeless, as it attaches to the tractor. Nov 19 03, 8:42 PM

lothruin

I work for a trucking company. The term semi does relate to the trailer. It stems from "semi-trailer", called thus because the trailer only has wheels on the back half. Therefore, a semi-trailer truck, referring to the tractor portion, is a tractor that pulls a semi-trailer. Understand that this is from an American's viewpoint, and terminology may be different in other parts of the world. Nov 19 03, 10:44 PM

mumby21

In Australia the semi trailer is made up of two parts - the prime mover and the trailer or in the case of a road train, trailers. Nov 20 03, 4:14 AM

dualkubota

It's called a semi because it's exactly half the length of a railroad car. Semi means half. A railroad car that's half the length of the regular ones is also called a semi. 40 feet, full size railroad car is 80 feet. Did you ever see them load truck trailers on a train? They load two truck trailers on one RR flat car. Jun 08 07, 4:07 AM

McGruff

Definition of a semitrailer or semi-trailer: noun: a type of trailer that has wheels only at the rear, the front end being supported by the towing vehicle (the towing vehicle is known as a tractor) Source: The Collins English Dictionary © 2000 HarperCollins Publishers A semi-trailer is a trailer without a front axle. A large proportion of its weight is supported either by a road tractor or by a detachable front axle assembly called a dolly. A semi-trailer is equipped with legs that can be lowered to support it when it is unhooked from the tractor. When coupled together, the tractor- trailer combination is often referred to as a semi, 18-wheeler, big-rig, articulated lorry, or truck and trailer. The purpose of a semi-trailer is to carry freight. There are several types of semi-trailers including dry freight vans, refrigerated vans (reefers), flatbeds, and tank trailers http://www.amtrex.net/semitrailer_definition.htm Jun 08 07, 6:55 AM

McGruff

I'm not finding a reference relating the term "semi" with half a railroad car, but it does make sense and could be where the name originated. A semi-trailer is a trailer without a front axle. A large proportion of its weight is supported either by a road tractor or by a detachable front axle assembly known as a dolly. A semi-trailer is normally equipped with legs which can be lowered to support it when it is uncoupled. A road tractor coupled to a semi-trailer is often called a semi-trailer truck or semi. http://www.answers.com/topic/semi-trailer A semi-trailer truck or tractor-trailer (colloquially known as a transfer truck, 18-wheeler, semi, or big-rig in the U.S.; as a semi in Australia, and Canada; and as an articulated lorry (artic), or truck and trailer in the UK, Ireland, and New Zealand) is an articulated truck or lorry consisting of a towing engine (tractor in the U.S., prime mover in Australia, and truck in the UK, Canada and New Zealand), and a semi-trailer (plus possible additional trailers) that carries the freight.In the UK, the term juggernaut is sometimes used for especially large articulated lorries. http://en.wikipedia.org/wiki/Semi-trailer_truck Jun 08 07, 7:10 AM

Baloo55th

In the UK, juggernaut has political or nimby connotations. It's only used in adverse comments. Truck isn't normally used for the front part of an artic - a truck tends to be a rigid wagon. The whole two-part thing is referred to as an artic, and the front bit is usually a tractor or tractor unit. If you need to differentiate it from a farm tractor, you say artic tractor. In the UK, only showmen and agricultural operators can tow more than one trailer at a time. Showmen are travelling fairs, circuses, etc who pay a different rate of road tax, Agricultural also pays a different rate of tax, and farm tractors and some other vehicles may use red diesel (duty free fuel) on the road. The trailer part of an artic is often referred to as a semi-trailer, and it's not to do with carriage on railways here, because they don't carry artics on the rails here. The loading gauge won't allow it. Only in the Channel Tunnel do wagons ride the rails. Jun 08 07, 8:02 AM

keotaman

dualkubota's answer is just a tad off. RR freight cars are 40', passenger cars are approx. 85'. No connection to the term semi in RR usage. While semi often means half, semi here is used in the sense of: "3 a: partial : incomplete b: having some of the characteristics of " Keo Sep 23 08, 11:07 AM

OneHoof

The vehicles commonly referred to as "semi trucks" are often the biggest vehicles on any stretch of road. Considering that "semi" means "half," it's natural to wonder, semi-what? The answer is: semi-trailer. Trucks The typical truck you see on the highway consists of two parts: the tractor and the trailer. Tractor The tractor is the part that does the pulling. It includes the driver's cab and the engine, and it can get around on its own. Trailer The trailer is filled with cargo, and it is dead weight. It's not going anywhere without a tractor to pull it. Semitrailers If a trailer has wheels on both ends and is pulled behind the tractor, it's a full-scale trailer. If it has wheels on only the back end, and the front rests on the tractor itself, it's a semi-trailer. In common parlance, then, a "semi" is a tractor pulling a semi-trailer. 18-Wheelers The most common tractor-trailer configuration in North America is the 18-wheeler semi. The tractor has a front axle with two wheels, and two rear axles with four wheels each, for a total of 10. The trailer has two rear axles with four wheels each, for a total of eight. Source: Turek Trucking: Tractor/Trailer Terms Read more: Why is it called a semi truck? | Answerbag http://www.answerbag.com/q_view/1941761#ixzz19t7qsrxd Jan 02 11, 7:28 AM

OneHoof

I was a truck driver for seven years in the United States. My understanding was that the term semi comes from the most basic definition meaning partial or incomplete. When driving a road tractor without the trailer, the truck would actually NOT stop as fast, because the laws of physics push the vast majority of the truck's weight onto the steer tires when braking... So, ironically a tractor which is incomplete (or semi complete) takes longer to stop then a tractor which is complete with its trailer. This is true because when you have a trailer with a load, you have the weight of the load keeping pressure on 18 wheels which with the tractor, trailer combination together has 5 axles, which have 10 drum brakes stopping capacity. If you ever watch a truck driving without its trailer you will notice its rear drive tires bob up and down... especially when not on a smooth road. Hence truck driver's call the tractor... which is incomplete and NOT as safe without its trailer, a "bob tail"... because while going down the road, it's back end or tail is bobbing up and down. So, on the CB... other truckers either call a truck without its trailer a bob tail a bob tail or a semi... meaning the truck was incomplete. In my 7 years of truck driving I have never heard the trailer called a semi... I have heard a road tractor called: a tractor, big truck, a ten wheeler, rig, but most often a "bob tail" or just a "semi truck". My understanding has always been the tractor is called a "semi" because it was incomplete, and NOT as safe to drive without the trailer. I came on this web site because my brother in law told me he looked up "semi" in the dictionary and that I was wrong. He claimed the dictionary referred to the trailer as the "semi". So, I want to correct myself if I am wrong. Hence, I came here to do research... and tell what I know as an experienced driver of 18 wheelers. Which still makes sense... the trailer is also incomplete without a tractor. I guess actually even more so because it can't even move without the tractor's tires to complete it. Of course, for several years it has driven me nuts when a news reporter says a "semi" has overturned on the interstate... and in the same breath say, it will take hours to clean up as crews are unloading the trailer by hand because either way, it is incorrect to call a tractor with its trailer a semi because "semi" means incomplete... and when they are both together they are complete and hence no longer "semi". Granted, the misnomer "semi" the reporter uses, is so over misused that the average radio listener accepts the incorrect term as normal vernacular. I guess the reporter uses "semi truck"... so people know it is an 18 wheeler or road tractor. Again, this gets on my nerves because either way, neither the tractor, nor the trailer are "semi" (incomplete) when they are attached to each other. So, the bottom line is: If the tractor is attached to a trailer you can no longer "correctly" call the combination a semi. It has now become a tractor (meaning to pull) and a trailer (which means to be pulled behind). So, from my perspective, I have always called my road tractor a "semi" truck, because I know it is semi complete without its trailer and I have to use extra caution and diligence when needing to stop, to keep from skidding. My brother in law caused me to realize... the trailer is also "semi" complete without its tractor to pull it where it needs to go. I will look into this deeper and let you know what I find. Thanks for reading. One Hoof Jan 02 11, 7:29 AM