Jackknifing refers to the folding of an articulated vehicle so that it resembles the acute angle of a folding pocket knife. If a vehicle towing a trailer skids, the trailer can push the towing vehicle from behind until it spins the vehicle around and faces backwards. This may be caused by equipment failure, improper braking, or adverse road conditions such as an icy road surface. In extreme circumstances, a driver may attempt to jackknife the vehicle deliberately in order to halt it following brake failure.

Jackknifing and Trailer swing
How a truck jackknifes

Trailer swing

When a trailer skids to one side, this is known as a trailer swing or trailer slew. This could happen on a slippery road surface, often where there is a cant. This is not the same as "jackknifing" and is not as serious since the trailer moves back into line as the vehicle continues forwards. The driver must be aware, however, that the trailer could slide up against parked cars or a guard rail, or the wheels could slide into a ditch. This situation can occur especially when the trailer is empty or lightly loaded, and weather conditions cause violent gusts of crosswind.

Anti-jackknife devices

  • One system with limited success was a device that mechanically limited the angle which a trailer could swing.
  • A much more successful system was to fit the tractor with anti-lock brakes. Fitted originally to airplanes in the 1950s, anti-lock brakes have significantly reduced the number of heavy vehicle accidents.
  • Electronic brakeforce distribution varies the pressure to the rear brakes during heavy load or hard braking, enhancing driver control.[1]
  • Tractors used to be fitted with a lever in the cab to operate the trailer brakes. The vehicle could be slowed down or stopped using the trailer brakes only. Theoretically this was a sure way to prevent jackknifing, but this lever was often the cause of jackknifing in a roundabout way. Frequent use of the trailer brakes alone caused them to overheat and fade while the tractor brakes remained fresh. In the event of an emergency stop, the driver would go straight for the foot brake and the truck would surely jackknife because the tractor brakes would lock while the trailer brakes would be ineffective due to previous overheating.
  • An alternative to having a trailer brake lever in the cab is to fit the trailer with an electromagnetic brake.

See also


  1. ^ Brake Pressure Regulator - Patent 3762776
Articulated vehicle

An articulated vehicle is a vehicle which has a permanent or semi-permanent pivot joint in its construction, allowing the vehicle to turn more sharply. There are many kinds of articulated vehicles, from heavy equipment to buses, trams and trains. Steam locomotives were sometimes articulated in that the driving wheels could pivot around.

In a broader sense, any vehicle towing a trailer or semi-trailer could be described as articulated (the word articulated comes from the Latin articulus : small joint). In the UK, the term "articulated lorry" refers to the combination of a tractor and a trailer, abbreviated to "artic". In the U.S., this is called a semi-trailer truck, "tractor-trailer" or "semi-truck" and would not necessarily be called articulated.

Brace position

To assume a brace or crash position is an instruction that can be given to prepare for a crash, such as on an aircraft; the instruction to 'brace for impact!' or 'brace! brace!' is often given if the aircraft must make an emergency landing on land or water. There are many different ways to adopt the brace position, with many countries adopting their own version based on research performed by their own aviation authority or that of other countries. The most common in passenger airliners being the forward-facing seat version, in which the person bracing places their head against or as close as possible to the surface it is likely to strike in the process bending over some degree, placing their feet firmly on the floor, and their hands either on their head or the seat in front.

Caravan (towed trailer)

A caravan, travel trailer, camper or camper trailer is towed behind a road vehicle to provide a place to sleep which is more comfortable and protected than a tent (although there are fold-down trailer tents). It provides the means for people to have their own home on a journey or a vacation, without relying on a motel or hotel, and enables them to stay in places where none is available. However, in some countries campers are restricted to designated sites for which fees are payable.

Caravans vary from basic models which may be little more than a tent on wheels to those containing several rooms with all the furniture and furnishings and equipment of a home. They are used principally in North America, Europe, Australia and New Zealand.

Computational phylogenetics

Computational phylogenetics is the application of computational algorithms, methods, and programs to phylogenetic analyses. The goal is to assemble a phylogenetic tree representing a hypothesis about the evolutionary ancestry of a set of genes, species, or other taxa. For example, these techniques have been used to explore the family tree of hominid species and the relationships between specific genes shared by many types of organisms. Traditional phylogenetics relies on morphological data obtained by measuring and quantifying the phenotypic properties of representative organisms, while the more recent field of molecular phylogenetics uses nucleotide sequences encoding genes or amino acid sequences encoding proteins as the basis for classification. Many forms of molecular phylogenetics are closely related to and make extensive use of sequence alignment in constructing and refining phylogenetic trees, which are used to classify the evolutionary relationships between homologous genes represented in the genomes of divergent species. The phylogenetic trees constructed by computational methods are unlikely to perfectly reproduce the evolutionary tree that represents the historical relationships between the species being analyzed. The historical species tree may also differ from the historical tree of an individual homologous gene shared by those species.

Drifting (motorsport)

Drifting is a driving technique where the driver intentionally oversteers, with loss of traction, while maintaining control and driving the car through the entirety of a corner. The technique causes the rear slip angle to exceed the front slip angle to such an extent that often the front wheels are pointing in the opposite direction to the turn (e.g. car is turning left, wheels are pointed right or vice versa, also known as opposite lock or counter-steering). The sport of drifting is not to be confused with the four wheel drift, a classic cornering technique established in Grand Prix and sports car racing. The traditional way of drifting is clutch kicking, then intentionally oversteering, and countersteering right after.

As a motoring discipline, drifting competitions were first popularized in 1970s Japan and further popularized by the 1995 manga series Initial D. Drifting competitions are held worldwide and are judged according to the speed, angle, showmanship and line taken through a corner or set of corners. The desired line is usually dictated by the judge or judges, who describe their desired line as well as highlight areas of importance, such as clipping zones, clipping points and touch and go areas.


Fishtailing is a vehicle handling problem which occurs when the rear wheels lose traction, resulting in oversteer. This can be caused by low friction surfaces (sand, gravel, rain, snow, ice, etc.). Rear-drive vehicles with sufficient power can induce this loss of traction on any surface, which is called power-oversteer.

During fishtailing, the rear end of the car skids to one side, which must be offset by the driver counter-steering, which is turning the front wheels in the same direction as the skid, (e.g. left if the rear swings left) and reducing engine power. Overcorrection will result in a skid in the opposite direction; hence the name. Without a proper driver's reaction, the fishtailing vehicle will spin completely.

Friction is the main reason this action is effective. If a car is moving across a surface in any direction other than the direction it is pointed, it is skidding (or sliding), and a sideways load is being imposed against the tires. This causes a lot of friction, even if the tires are allowed to rotate freely. By turning the front wheels into the direction of the skid, the front wheels will become aligned with the direction of travel. The side load will no longer be imposed against the front tires, and they will then roll freely to match the speed of the vehicle. This reduces the friction between the front tires and the surface. But the rear tires will still be sliding sideways, and the greater friction that exists will cause the back end to trail directly behind the front end, similar to a badminton birdie in flight, thus the car straightens out. As the car straightens, the front wheels must be kept aligned with the direction of travel to keep the friction of the front tires at or below the friction of the rear tires, or a skid in the opposite direction will quickly develop. The key is to keep the front wheels aligned with the direction the vehicle is moving-not the direction it is pointed.Most modern rear wheel drive cars solve this problem by using a form of traction control which limits engine power when fishtailing occurs. The ability of the rear suspension to keep tires in contact with, and perpendicular to the road is also a key factor in the amount of grip available through the rear axle. For example, a live beam axle suspension will have far less grip on a bumpy road than an independent rear suspension, due to its far greater unsprung weight, and forces from one wheel being transmitted through the axle to the other wheel, leading to the tire being out of contact with the road surface more of the time

Similar behaviour is evident during heavy braking in all types of road vehicles, due to weight transfer to the front. This can be mitigated by re-proportioning the braking forces (more to the front, less to the rear) to keep the rear wheels from locking up. Most modern cars use anti-lock brakes (ABS) which addresses this problem. Older cars may have less sophisticated technical systems for lessening this tendency or the driver alone must actively modulate the brakes.

Fishtailing may be the result of the police pursuit technique called the PIT maneuver, in which the driver of a pursuing vehicle deliberately induces directional instability in a pursued vehicle.

Free surface effect

The free surface effect is a mechanism which can cause a watercraft to become unstable and capsize.It refers to the tendency of liquids — and of unbound aggregates of small solid objects, like seeds, gravel, or crushed ore, whose behavior approximates that of liquids — to move in response to changes in the attitude of a craft's cargo holds, decks, or liquid tanks in reaction to operator-induced motions (or sea states caused by waves and wind acting upon the craft). When referring to the free surface effect, the condition of a tank that is not full is described as a "slack tank", while a full tank is "pressed up".

Great East Thompson Train Wreck

The Great East Thompson Train Wreck was a large rail disaster which occurred in East Thompson, Connecticut, on December 4, 1891. It was one of the most extensive train wrecks in American history, and the only one to involve four trains. It happened on the New York and New England Railroad, which provided a shortcut from New York City to Boston by making a diagonal across Connecticut. The railroad is now abandoned, and most of its tracks removed.

Hans-Rudolf Künsch

Hans Rudolf Künsch (born 17 October 1951) is a Swiss mathematician and statistician based in Zürich, where he has been a professor with the Seminar für Statistik since 1983 at the Eidgenössische Technische Hochschule (Swiss Federal Institute of Technology). As of 2007, Künsch is the Chair of ETH Zürich's Department of Mathematics. He was a co-editor of the leading journal Annals of Statistics during the 1998–2000 period and has served on the Council of the worldwide organisation Institute of Mathematical Statistics.

Künsch worked as a research student at the University of Tokyo with a scholarship grant from the Japanese government. After completing his PhD at ETH Zürich, with a dissertation project on Reellwertige Zufallsfelder auf einem Gitter: Interpolationsprobleme, Variationsprinzip und statistische Analyse, he returned to research work in Japan, at the University of Tokyo and the Institute of Statistical Mathematics. Since 1983 he has held various academic positions with his alma mater ETH Zürich.

Professor Künsch's main research areas are spatial statistics and random fields (geostatistics, parameter estimation for Gibbs fields, image analysis, space-time models); time series analysis (long range dependence, bootstrap methods for dependent data, general state-space models); and robust statistics and statistical model selection. Among his most frequently cited contributions is the Annals of Statistics 1989 article on bootstrapping and jackknifing in stationary time series.


Jackknife may refer to:

Pocket knife or jackknife, a compact, foldable knife

Jackknifing, a type of crash with articulated vehicle combinations

Molecular phylogenetics

Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominately in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to determine the processes by which diversity among species has been achieved. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree. Molecular phylogenetics is one aspect of molecular systematics, a broader term that also includes the use of molecular data in taxonomy and biogeography.Molecular phylogenetics and molecular evolution correlate. Molecular evolution is the process of selective changes (mutations) at a molecular level (genes, proteins, etc.) throughout various branches in the tree of life (evolution). Molecular phylogenetics makes inferences of the evolutionary relationships that arise due to molecular evolution and results in the construction of a phylogenetic tree. The figure displayed on the right depicts the phylogenetic tree of life as one of the first detailed trees, according to information known in the 1870s by Haeckel.

Recurring Saturday Night Live characters and sketches introduced 2003–2004

The following is a list of recurring Saturday Night Live characters and sketches introduced between October 4, 2003, and May 15, 2004, the twenty-ninth season of SNL.

Resampling (statistics)

In statistics, resampling is any of a variety of methods for doing one of the following:

Estimating the precision of sample statistics (medians, variances, percentiles) by using subsets of available data (jackknifing) or drawing randomly with replacement from a set of data points (bootstrapping)

Exchanging labels on data points when performing significance tests (permutation tests, also called exact tests, randomization tests, or re-randomization tests)

Validating models by using random subsets (bootstrapping, cross validation)

SS Schenectady

The SS Schenectady was a T2-SE-A1 tanker built during World War II for the United States Maritime Commission.

She was the first tanker constructed by the Kaiser Shipbuilding Company shipyard at Swan Island in Portland, Oregon. The keel of the Schenectady was laid on 1 July 1942, the completed hull launched on 24 October, and she was declared completed on 31 December, six months after construction began and two and a half months ahead of schedule.


A semi-trailer is a trailer without a front axle. In the United States, the term is also used to refer to the combination of a truck and a semi-trailer, a tractor-trailer.A large proportion of a semi-trailer's weight is supported by a tractor unit, or a detachable front-axle assembly known as a dolly, or the tail of another trailer. A semi-trailer is normally equipped with landing gear (legs which can be lowered) to support it when it is uncoupled. Many semi-trailers have wheels that are capable of being totally dismounted and are also relocatable (repositionable) to better distribute load to bearing wheel weight factors. Semi-trailers are more popular for transport than full trailers, which have both front and rear axles. Ease of backing is cited as one of the semi's chief advantages. A road tractor coupled to a semi-trailer is often called a semi-trailer truck or "semi" in North America & Australia, and an articulated lorry or "artic" in the UK.

Semi-trailers with two trailer units are called B-doubles (Australian English) or tandem tractor trailers, tandem rigs, or doubles (American English). Other terms used are "B-train" or (when there are three or more trailers) "road train". A double-trailer combination is possible with the use of a dolly, or "converter dolly" (Australian and American English), essentially one to three additional axles placed under the front of a second semi-trailer. The first semi-trailer is connected to the power unit using the tractor's fifth wheel coupling while the converter dolly, already attached to the second semi-trailer, is connected to the first semi-trailer with a drawbar. In Australian English, the tractor unit is called a "prime-mover", and the combination of a prime-mover and trailer is known as a "semi-trailer", "semi" or single.

Semi-trailer truck

A semi-trailer truck (more commonly semi truck or simply "semi") is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer attaches to the tractor with a fifth-wheel coupling (hitch), with much of its weight borne by the tractor. The result is that both the tractor and semi-trailer will have a design distinctly different from that of a rigid truck and trailer.

It is variously known as a semi, semi-Truck or Transporter in Canada; semi or single in Australia and New Zealand; semi, tractor-trailer, big rig, or eighteen-wheeler in the United States; and articulated lorry, abbreviated artic, in the United Kingdom, Ireland and New Zealand.

Siemens ACS-64

The Siemens ACS-64, or Amtrak Cities Sprinter, is an electric locomotive designed by Siemens Mobility for use on the Northeast Corridor (NEC) and the Keystone Corridor in the northeastern United States. The design was based on locomotives Siemens created for use in Europe and Asia, but with changes to comply with American standards. The ACS-64 is built at the Siemens factory in Florin, California, located outside of Sacramento.

The first 70 locomotives were built for Amtrak to replace the railroad's fleet of aging AEM-7 and unreliable HHP-8 locomotives. The first ACS-64 entered service in February 2014 and deliveries continued until August 2016.

SEPTA Regional Rail in Southeastern Pennsylvania operates a fleet of 15 ACS-64s since August 2018, on the agency's commuter rail routes.

The Man with Two Brians

"The Man with Two Brians" is the fifth episode in the seventh season of the American animated television series Family Guy. It premiered on Fox in the United States on November 9, 2008. The episode centers on anthropomorphic dog Brian after he is injured during a stunt being enacted by his owner, Peter, after he watches Jackass with his friends. The family comes to realize that Brian may be getting too old, so Peter brings home a new, optimistic dog. Brian is prompted to leave when his family begins to favor New Brian over him.

The episode was written by John Viener and marked the directorial debut of Dominic Bianchi. It received generally favorable reviews from critics for its storyline and various cultural references. According to Nielsen ratings, the episode was viewed by 8.60 million households in its original airdate. Johnny Knoxville, Will Sasso and Camille Guaty provided guest performances in the episode.

Yishai Romanoff

Yishai Romanoff (born 1986) is an American Hasidic musician, best known as the lead singer for the Breslov punk band Moshiach Oi!. Romanoff, as well as the rest of the band, is featured prominently in the 2012 documentary Punk Jews. He is also a drummer for Shabasa labelmates Blanket Statementstein, RockaZion, and Shin Shin Mem.

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