A History and Overview of the Trucking Industry Part 1
Truck Terminology and Designs
Trucks started as a way of transporting goods during the early twentieth century. They were powered by using steam or internal combustion engines. Drivers of trucks were called teamsters because oftentimes teams of horses were used. A truck offered many advantages over using horses, oxen or even humans. They could carry goods further and over longer periods of time and they were more cost effective than previous methods.
The need for vehicles that could carry more weight safely, reliably and cheaply led to the design of great ideas. Solid rubber tires on wooden spoke wheels were replaced with pneumatic tires on steel wheels. The most efficient power source proved to be internal combustion. Steam still remained popular in American heavy equipment and European trucks even though it was no longer used by American trucks.
During the 1920s, engines could produce approximately 24 horsepower. Today, engines can produce up to 600 horsepower. As engines became more and more powerful, trucks could go faster and faster. Some early designs had top speeds designed to keep up with a mule train. By the early 1950s, top truck speeds could be as high as 50 miles per hour. Today’s technologically advanced trucks can go 75 miles per hour or faster, although many trucks have governors to limit speed.
Engineers and designers tried positioning various truck components on the chassis to get a favorable result. The design we use today evolved between 1905-1910 and is still the most popular. First in front is cooling followed by the engine, transmission, drive shaft and rear drive axle. The truck operator sits either behind or above the engine and the cargo follows. Refining truck components and systems to meet the demands of government regulations, global competition and emission standards makes truck design an on-going process.
Specific loads have led to the creation of customized trailers. A refrigerated trailer, a dump truck and a tanker were developed to meet specific needs. Even today, customized trailers are being developed to haul specific cargo to meet the on-going needs of transporting large and heavy items.
The term “truck” refers to a vehicle that hauls cargo. Vehicles designed to haul passengers are described as buses, passenger buses and coaches. A straight truck is an all-in-one self-contained power and cargo carrying vehicle. Some straight trucks can pull additional trailers.
A combination vehicle is a power unit, usually a tractor, pulling a separate cargo unit, a semi trailer. A parcel delivery van or step van is built on a light duty truck chassis but is not usually referred to as a truck. Tractors are specifically designed to haul trailers, but they can be driven without a semi trailer attached to them. Driving a tractor without a trailer attached is called bobtailing. A bobtail is any straight truck or tractor not attached to or pulling a trailer.
Straight trucks and tractors have the same components as regular automobiles: a chassis, engine, transmission, drive shaft, wheels, tires and axles. However, the components on a straight truck or tractor are larger, stronger and more durable and are specifically designed to stand up to extreme usage and conditions.
Straight trucks and tractors have cabs which is where the driver operates. The cab contains the driver compartment and operating controls. Some trucks have a compartment called a sleeper, which is like a bedroom for long haul drivers. The sleeper has a bed or bunk beds, and places to store personal effects. They often have audio and visual entertainment. The sleeper is located right behind the driver compartment with an opening between each. A tractor that has an attached sleeper is called a sleeper cab.
Tractors and trucks are classified into two categories based on their cab configuration. They can be termed conventional or a cab-over-engine (COE). On a conventional tractor, it has a forward-hood design where the cab sits behind the engine. On a cab-over-engine, the cab is right on top of the engine compartment.
Because of the shorter wheelbase on cab-over-engines, they are typically used in congested city or delivery operations; this allows for better maneuverability and visibility compared to a regular tractor. Many tractor manufacturers are making conventional tractors with a set-back front axle in order to shorten the wheelbase and improve maneuverability.
Tractors are made with varying hood designs to accommodate different engine designs, variations in style, or to improve aerodynamics. Many of today’s conventional tractors are being made with shorter and more aerodynamic hoods.
Tractors come in a variety of hood designs. Some have the “boxy” looking familiar hood, which is called a conventional tractor. Some conventional tractor hoods have an extended hood, usually six to twelve inches longer than a traditional hood. This is a carry-over style from previous hood designs when engines were longer. A hybrid tractor is a short nose conventional and is like a cab-over-engine in that it has a shorter wheel base, is often made with two axles and is usually used in short hauls with one or two 24” – 28” trailers.
Trucks and tractors are made with two or more axles to support vehicle and cargo weight. The front axles have steerable wheels and are called steer axles or drive axles. Tandem axles are non-steer axles usually found on the rear of tractors. Tandems carry more weight than single rear axles.
Every truck has one or more axles that receive power from the engine and transmits it to the wheels. The drive axles can either be single or in tandem. If both axles of a tandem are drive axles, they are called tandem drive axles or twin screws. A pusher axle is a front axle of a tandem, a non-drive axle. If it is a rear non-drive axle of the tandem it is called a tag axle.
A headache rack or headerboard is used to secure cargo and protect the driver. It is mounted on the frame behind the cab or sleeper berth. It protects the cab if an object moves forward on the unit bed as well as protects the driver and/or passengers. It also provides storage for chains and/or chain binders which are used to strap down cargo. A bulkhead does the same thing as a headache rack except it’s mounted on the front of the trailer. See the regulatory requirements 393.106 of the Federal Motor Carrier Safety Regulations.
A straight truck holds the cargo and power unit directly on the chassis. This type of truck can be used for long distance hauling, but is more commonly used as a pickup and delivery vehicle within a short range.
Trailers
Trailers are separate units from the tractor designed to hold or carry cargo. Trailers are designed to be towed by a power unit such as a tractor or truck and do not have engines. They can have only one axle or as many axles are necessary to haul a load. In order to carry heavier loads, more axles must be added to lengthen the wheelbase. Just like tractors have tandems, so do trailers. Three axles put together are termed triaxle. A tandem axle tractor usually has two drive axles, or twin screws which give the truck more traction in slippery or adverse conditions.
Both straight trucks and truck tractors have a front axle and one or several rear axles. The front axle is called the steering axle while the rear axle that is powered is called the drive axle. Some tandems will have only one drive axle. The non-driven axle can be a tag axle (located behind the drive axle) or a pusher axle (located ahead of the drive axle).
A full-trailer supports the cargo weight and its entire weight on its own tires. It can be pulled by a straight truck or a tractor. The vehicle to which it is attached only supports a small amount of the weight or none at all as it pulls it down the road. However, a semi-trailer depends on the towing vehicle to support a big part of its weight, sometimes as much as 50%.
When a trailer is not hooked up to a tractor, the weight of the semi-trailer and cargo are supported by trailer axles and supported by the landing gear located near the front of the trailer.
The process of connecting a tractor to a semi-trailer is called coupling. This will create what is commonly referred to as a tractor-trailer combination or an articulated vehicle. Once the semi-trailer is coupled to a tractor, the landing gear is raised and is no longer supporting the trailer’s weight. Semi-trailers are so common in the trucking industry that they are typically referred to as trailers.
The joining of the two units is made possible by a fifth-wheel located on the rear of the tractor and the kingpin, located underneath the front of the semi-trailer. The fifth-wheel is a flat circle-shaped plate attached to the tractor’s chassis which has locking jaws into which the trailer’s kingpin sits. When it comes in contact, the jaws latch automatically and require a lever to be pulled to release it again. It secures the trailer’s kingpin and transfers the weight of the trailer to the tractor. The fifth wheel is the pivot point between the tractor and the trailer.
The most common type of kingpin is almost 3.5” long, 2” in diameter and is usually welded to the center of the fifth-wheel plate. As a tractor is backed towards the semi-trailer, the fifth-wheel contacts and slides under the fifth-wheel plate to lock it into place.