Traction refers to the friction between a drive member and the surface it moves upon, where the friction is used to provide motion.

For the purposes of driving a wheeled vehicle, high friction is generally desired, as it provides a more positive connection between the driving and driven members. In contrast, motion in a geared mechanism is provided by interference, and friction is usually detrimental because the gear mechanism has intrinsic sliding, and sliding under friction causes heating losses.

Traction between two surfaces usually depends on several factors including:

• Material properties of each surface
• Macroscopic and microscopic shape or “roughness”
• Force of contact
• Area of contact
• Contaminants at the material boundary including lubricants and adhesives

The Corporate Average Fuel Economy (CAFE) regulations in the United States, first enacted by Congress in 1975, exist to regulate and improve the average fuel economy of cars and light trucks (trucks, vans and sport utility vehicles) sold in the U.S. in the wake of the 1973 Arab Oil Embargo. It is the sales-weighted average fuel economy, expressed in miles per gallon (mpg), of a manufacturer’s fleet of passenger cars or light trucks with a gross vehicle weight rating (GVWR) of 8,500 pounds (3,856 kg) or less, manufactured for sale in the United States, for any given model year. The National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA) regulate CAFE standards.

If the average fuel economy of a manufacturer’s annual car or truck production falls below the defined standard, the manufacturer must pay a penalty, currently $5.50 per 0.1 mpg under the standard, multiplied by the manufacturer’s total production for the U.S. domestic market.

CAFE – Calculation

For the purposes of CAFE, a manufacturer’s car output is divided into a domestic fleet (vehicles with more than 75% U.S., Canadian or (after the passage of NAFTA) Mexican content) and a foreign fleet (everything else). Each of these fleets must separately meet the requirements. This requirement was designed to benefit the American automobile industry, but it is regarded as having little effect and the possibility of removing the two fleet rule is being considered. The two fleet rule for light trucks was removed in 1996.

Alternative fuel vehicles are treated as if they are substantially more fuel efficient, as an incentive to develop alternative fuel vehicles.

Manufacturers are also allowed to earn CAFE “credits” in any year they exceed CAFE requirements, which they may use to offset deficiencies in other years. CAFE credits can be applied to the three years previous or three years subsequent to the year in which they are earned. The reason for this requirement is so that manufacturers are not penalized for occasionally (due to market conditions, for example) failing the targets, but only for persistent failure to meet them.

CAFE – Current Standards

Cars and light trucks are considered separately for CAFE and are held to different standards. As of early 2004, the average for cars must exceed 27.5 mpg and the light truck average must exceed 20.3 mpg. Trucks under 8500 lb must average 22.5 mpg in 2008, 23.1 mpg in 2009, and 23.5 mpg in 2010. After this, new rules set varying targets based on truck size and class.

Overall fuel economy for cars and light trucks in the U.S. market reached its highest level in 1987, when manufacturers managed 22.1 mpg (10.6 L/100 km). The average in 2004 was 20.8 mpg. In that time, vehicles increased in size from an average of 3,220 pounds to 4,066 lb (1,461 kg to 1,844 kg).

A number of manufacturers choose to pay CAFE penalties rather than attempt to comply with the regulations. As of model year 2002, BMW, DaimlerChrysler (import fleet only), Fiat, Lotus and Porsche failed the automobile CAFE requirement, while BMW and Volkswagen failed to meet the light truck requirement.

CAFE – Future Rules and Standards

The CAFE rules for trucks were officially amended at the end of March, 2006. These changes would segment truck fleets by vehicle size and class as of 2011. All SUVs and passenger vans would now have to comply with CAFE standards regardless of size, but some large pickup trucks and cargo vans would remain exempt.

The fuel economy for a vehicle will be dictated by its “footprint” – the product of its wheelbase and track. Some critics point out that this may have the unintended consequence of pushing manufacturers to make ever-larger vehicles to avoid strict economy standards.

CAFE – Criticism

The CAFE standards have come under attack by think tanks such as the Heritage Foundation and the Competitive Enterprise Institute, primarily on the basis that the cheapest way for automotive manufacturers to increase mileage is to reduce vehicle weight, which makes vehicles inherently less safe in accidents (this point is disputed however). Both groups note almost an exact correlation between increased CAFE standards and increased highway deaths (although correlation does not prove causation).

Lumbar Vertebrae

The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and can be distinguished by the absence of a foramen (hole) in the transverse process, and by the absence of facets on the sides of the body.

General Lumbar Vertebrae Characteristics

These are the general characteristics of the first through fourth lumbar vertebrae. The fifth vertebra contain certain peculiarities, which are detailed below.

As with other vertebrae, each lumbar vertebra consists of a vertebral body and a vertebral arch. The vertebral arch, consisting of a pair of pedicles and a pair of laminae, encloses the vertebral foramen (opening) and supports seven processes.

Vertebral Body

The vertebral body of each lumbar vertebra is large, wider from side to side than from front to back, and a little thicker in front than in back. It is flattened or slightly concave above and below, concave behind, and deeply constricted in front and at the sides.

Vertebral Arch

The Pedicles are very strong, directed backward from the upper part of the vertebral body; consequently, the inferior vertebral notches are of considerable depth.

The laminae are broad, short, and strong. The vertebral foramen is triangular, larger than in the thoracic vertebrae, but smaller than in the cervical vertebrae.

Processes

The spinous process is thick, broad, and somewhat quadrilateral; it projects backward and ends in a rough, uneven border, thickest below where it is occasionally notched.

The superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles and laminae. The facets on the superior processes are concave, and look backward and medialward; those on the inferior are convex, and are directed forward and lateralward. The former are wider apart than the latter, since in the articulated column the inferior articular processes are embraced by the superior processes of the subjacent vertebra.

The transverse processes are long and slender. They are horizontal in the upper three lumbar vertebrae and incline a little upward in the lower two. In the upper three vertebrae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from the pedicles and posterior parts of the vertebral bodies. They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs.

Of the three tubercles noticed in connection with the transverse processes of the lower thoracic vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mammillary process. The inferior is situated at the back part of the base of the transverse process, and is called the accessory process.

Peculiar Lumbar Vertebrae

Some individuals have four lumbar vertebrae, while others have six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these individuals.

Fifth Lumbar Vertebra

The fifth lumbar vertebra has certain peculiarities.

The fifth lumbar vertebra is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacrovertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes; and by the thickness of its transverse processes, which spring from the body as well as from the pedicles.

The fifth lumbar vertebra is by far the most common site of spondylolysis/spondylolisthesis.

Roll cages are often used in professional rally cars.

A roll cage is a specially constructed frame built around the cab of a vehicle to protect the driver from being injured in an accident, particularly in the event of a rollover. Roll cages extend in front of the driver, next to the A-pillar, to provide as much high-speed protection as possible in a coupe. This is compared to the protection provided in open wheel racing, where a solid shell encases the majority of the driver’s body in addition to a rollover hoop that extends over the driver’s helmet. A roll cage can also do a great deal to stiffen the chassis, which is desirable in racing applications.

Roll bar on an Esther.

A roll bar is a single bar behind the driver that provides moderate rollover protection. A targa top is a body style that integrates an externally-visible roll bar that a semi-convertible top attaches to. Convertibles have particular safety concerns for rollover protection. In most modern convertibles a strong windscreen frame acts as a roll bar.

Roll hoops on an Audi TT.

Roll hoops are essentially two roll bars, one behind the driver and one behind the passenger. Sometimes just a single roll hoop behind the driver is used. Sometimes they are integrated into the design of the body.

A gross vehicle weight rating (GVWR) is the estimated total weight of a road vehicle that is loaded to capacity, including the weight of the vehicle itself plus fuel, passengers, cargo, and other miscellaneous items such as extra aftermarket parts. In the United States, two important GVWR numbers are 6,000 pounds (2,721 kg) and 8,500 pounds (3,856 kg). Vehicles over 6,000 pounds are restricted from many city roadways (though there is some dispute about whether this restriction is for actual weight or GVWR). Vehicles over 8,500 pounds do not have to display EPA estimated fuel mileage or a Monroney sticker, nor are they subject to state emissions testing.

An SUV with four pillars.

An A-pillar is a name applied by car stylists and enthusiasts to the shaft of material that supports the windshield (windscreen) on either of the windshield frame sides. By denoting this structural member as the “A” pillar, and each successive vertical support after a successive letter in the alphabet (B-pillar, C-pillar etc.), this naming scheme allows those interested in car design to have points of reference when discussing design elements.

A “pillarless” hardtop vehicle, considered to have two total pillars.

A stretch limo with five pillars.

In the most usual configuration, the C-pillar supports the rear window, however, depending on configuration, the final pillar can be B, D, or even higher in more extreme examples.

Occasionally cars have a break between windows or doors, but have no supporting material in the space. These non-supporting breaks are not considered to be pillars, and are skipped for purposes of the alphabetical naming scheme. With the introduction of monocoque design in automobiles, supporting pillars have become increasingly important, and nearly every visual break in a modern vehicle contains a supporting pillar.

Consumer Reports is an American magazine published monthly by Consumers Union, a non-profit organization founded in 1936 by Arthur Kallet, Colston Warne, and others who felt that the established Consumers Research organization was not aggressive enough. According to the magazine’s website, it has approximately 4 million subscribers, and an annual testing budget of approximately $21 million U.S.

Consumer Reports is known for publishing reviews and comparisons of consumer products and services based on reporting and results from its in-house testing laboratory. Consumer Reports does not accept advertising nor permit the commercial use of its reviews for selling products. Consumer Reports’ tests and ratings of appliances, foods, automobiles and other products/services are highly respected. The annual Consumer Reports new car issue, released every March, is typically the magazine’s best-selling issue and is thought to influence millions of automobile purchases.

All tested products are purchased at retail by Consumer Reports staff. No free samples are accepted from manufacturers, a policy which has tradeoffs. With short life-cycle products such as electronics, it is not unusual to find the reviewed product has been replaced or discontinued prior to the publication of the review.

Consumers Union also publishes ConsumerReports.org. With millions of readers, it has more paid subscribers than any other publication-based website. While most of its information comes at a small fee, in 2002 Consumers Union launched Consumer Reports WebWatch. The grant-funded project seeks to improve the credibility of websites through investigative reporting, publicizing best-practices standards, and publishing a list of sites that comply with the standards. Its content is free. In 2005 Consumers Union launched Consumer Reports Best Buy Drugs. This service takes publicly available (but hard to digest) studies on pharmaceutical effectiveness and combines them with pricing information in an easy-to-read format.

Consumer Reports should not be confused with Consumers Digest, a for-profit publication which does accept advertisements and allows companies to use its reviews for marketing purposes. Nor should Consumer Reports be confused with ConsumerSearch, which reviews, analyzes, and summarizes reviews from a number of sources, rather than conducting any objective testing of products.

Lawsuits vs. Consumers Union

In 1984, Bose Corporation sued Consumer Reports for publishing a review in which Bose speakers did relatively poorly. The review stated that the stereo image of the Bose speakers was unstable and “tended to wander about the room”, undermining the basic Direct/Reflecting concept behind Bose’s products. The final verdict ruled that Consumer Reports had in fact libeled Bose by overstating its negative findings, which were, more precisely, that the stereo image merely “moved along the wall” behind the speakers. This was something of a Pyrrhic victory for Bose, who were now widely regarded as bullies by loyal Consumer Reports readership, the very demographic group towards whom Bose products were targeted. Furthermore, the monetary award of $210,000 in libel damages was appealed to the Federal Supreme Court, who overturned it. Nevertheless, the case is believed to have had a chilling effect on publication of subjective preferences in reviews, both specifically by Consumer Reports as well as in the media as a whole.

In 1996 Consumer Reports was the subject of a lawsuit by Suzuki Motors regarding a road test of the Suzuki Samurai that the magazine had published in 1988. Suzuki alleged that the magazine’s test of the company’s popular off-roader had been skewed so as to show that the vehicle was prone to tipping over during an avoidance test (an equivalent of other magazines’ “elk test”). The lawsuit was dismissed by mutual consent in 2004.

In 2003, Sharper Image sued Consumer Reports in California for product disparagement, over negative reviews of its Ionic Breeze Quadra air purifier. Consumer Reports moved for dismissal on October 31, 2003, under California’s Anti-SLAPP (Strategic Lawsuits Against Public Participation) law, and the case was dismissed in November 2004, on the grounds that the Sharper Image “has not shown that the test protocol used by Consumers Union was scientifically, or otherwise, invalid,” and had not “demonstrated a reasonable probability that any of the challenged statements were false.” The decision also awarded Consumers Union $525,000 in legal fees and costs.

Power steering is a system for reducing the steering effort on cars by using an external power source to assist in turning the wheels. Power steering was invented in the 1920s by Francis W. Davis and George Jessup in Waltham, Massachusetts. Chrysler Corporation introduced the first commercially available power steering system on the 1951 Chrysler Imperial under the name Hydraguide.

Hydraulic Power Steering Systems

Most power steering systems work by using a belt driven pump to provide hydraulic pressure to the system. This hydraulic pressure is generated by a rotary-vane pump which is driven by the vehicle’s engine. As the speed of the engine increases, the pressure in the hydraulic fluid also increases, hence a relief valve is incorporated into the system to allow excess pressure to be bled away.

While the power steering is not being used, i.e. driving in a straight line, twin hydraulic lines provide equal pressure to both sides of the steering wheel gear. When torque is applied to the steering wheel, the hydraulic lines provide unequal pressures and hence assist in turning the wheels in the intended direction.

Some more modern implementations of hydraulic systems also include an electronic pressure valve which can reduce the hydraulic pressure of the power steering lines as the vehicle’s speed increases (variable assist power steering).

Electric Power Steering Systems

Electric power steering, such as those found on the Acura NSX, use only electric components. Sensors detect the motion and torque of the steering column and a computer applies assistive power via electric motors. This allows varying amounts of assistance to be applied depending on driving conditions.

In contrast to hydraulic systems, with an electric system the “communication” is only one way. The steering wheel transmits forces to the front wheels assisted by the motors, but the forces on the front wheels are not transmitted back through the motors to the steering wheel. Electric-only systems thus do not provide as much feedback to the driver, a criticism commonly expressed as a lack of steering “feel”.

Electro-hydraulic Power Steering Systems

So called “hybrid” systems use the same hydraulic assist technology as standard systems, with the hydraulic pressure being provided by an electric motor instead of a belt driven one.

Understeer is a term for a car handling condition during cornering in which the circular path of the vehicle’s motion is of a markedly greater diameter than the circle indicated by the direction its wheels are pointed. The effect is opposite to that of the oversteer and in simpler words understeer is the condition in which the front tires don’t follow the trajectory the driver is trying to impose while taking the corner, instead following a more straight line trajectory.

This is also often referred to as pushing, plowing, or refusing to turn in. The car is referred to as being ‘tight’ because it is stable and far from wanting to spin.

As with oversteer, understeer has a variety of sources such as mechanical traction, aerodynamics and suspension.

Classically, understeer happens when the front tires have a loss of traction during a cornering situation, thus causing the front-end of the vehicle to have less mechanical grip and become unable to follow the trajectory in the corner.

In modern race cars, especially open-wheel cars, understeering is caused mainly due to the aerodynamic configuration. A lack of heavy aerodynamic load in the front of the vehicle prevents the front tires from gaining enough traction. At the same time, having a heavier aerodynamic load at the read-end of the vehicle gives the rear tires more traction than the front tires, which will cause understeer. Also, suspension balance should take into account the types of surfaces being driven – differing levels of friction in each surface influence the potential understeer behavior. Camber angles, ride height and tire pressure are important factors that determine the understeer/oversteer handling condition.

Understeer – Common practice

It is common practice among automobile manufacturers to configure production cars to have a slight understeer by default. If a car understeers slightly, it tends to be more stable if a violent change of direction occurs, improving safety.

Understeer Physics

Under all high speed (greater than approximately 10mph (16 km/h) for a typical automobile) cornering conditions a wheeled vehicle with pneumatic tires develops a greater lateral (i.e. sideslip) velocity than is indicated by the direction in which the wheels are pointed. The difference between the circle the wheels are currently tracing and the direction in which they are pointed is the slip angle. If the slip angles of the front and rear wheels are equal, the car is in a neutral steering state. If the slip angle of the front wheels exceeds that of the rear, the vehicle is said to be understeering. If the slip angle of the rear wheels exceeds that of the front, the vehicle is said to be oversteering.

An old bit of racing humor says that an understeering car goes through the fence nose first, an oversteering car goes through the fence tail first, and with a neutral-steering car, both ends go through the fence at the same time.

Understeer by Design

Any vehicle may understeer or oversteer at different times based on road conditions, speed, available traction, and driver input. The design of a vehicle, however, will tend to produce a particular “terminal” condition when the vehicle is pushed to and past its limits of adhesion. “Terminal understeer” refers to a vehicle which, as a function of its design, tends to understeer when cornering loads exceed tire traction.

Terminal handling balance is a function of front/rear relative roll resistance (suspension stiffness), front/rear weight distribution, and front/rear tire traction. A front-heavy vehicle with low rear roll stiffness (from soft springing and/or undersized or nonexistent rear anti-roll bars) will have a tendency to terminal understeer: its front tires, being more heavily loaded even in the static condition, will reach the limits of their adhesion before the rear tires, and thus will develop larger slip angles. Front-wheel drive cars are also prone to understeer because not only are they usually front-heavy, transmitting power through the front wheels also reduces their grip available for cornering.

Although understeer and oversteer can each cause a loss of control, many automakers design their vehicles for terminal understeer in the belief that it is easier for the average driver to control than terminal oversteer. Unlike terminal oversteer, which often requires several steering corrections, understeer can often be reduced simply by reducing speed.

Racing drivers generally prefer a neutral condition (with a slight tendency toward understeer or oversteer, depending on the track and driver preference) because both understeer and oversteer conditions will scrub off speed while cornering.

The spinal cord is a part of the vertebrate central nervous system that is enclosed in and protected by the vertebral column (it passes through the spinal canal). It consists of nerve cells. The cord conveys the 31 spinal nerve pairs of the peripheral nervous system, as well as central nervous system pathways that innervate skeletal muscles.

The vertebral column consists of vertebrae described as belonging to 5 groups. These groups are (in order from top to bottom): the cervical, thoracic, and lumbar vertebrae, and the sacrum and coccyx.

Spinal Cord Injury

Spinal cord injuries are caused by damage to the spinal cord, such as falling on the neck or back, or having the spinal cord moved or disrupted in another way. The vertebral bones or intervertebral disks can shatter, causing the spinal cord to be punctured by a sharp fragment of bone. Usually victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In good cases a victim might only suffer loss of hand or foot function. More severe injury may result in paraplegia, quadriplegia, or full body paralysis below the site of injury to the spinal cord.

The two most common areas of the spinal cord most injured are the cervical spine (C1-C7) and the lumbar spine (L1-L5). (The notation C1, C7, L1, L5 refer to the location of a specefic vertebra in either the cervical, thoracic, or lumbar region of the spine.)

Spinal Cord Anatomy

A human spinal cord.The spinal cord originates inside the brain at the inferior end of the medulla oblongata, exiting the skull via the foramen magnum. It is wrapped in three layers of membranes, called meninges.

The spinal cord carries sensory signals and motor innervation to most of the skeletal muscles in the body. Just about every voluntary muscle in the body below the head depends on the spinal cord for control. Similarly, most cutaneous sensation below the neck is transmitted via the spinal cord. Most of the sympathetic pathways and the lower (i.e. non-vagal) parasympathetic pathways also go through the spinal cord.

A cross-section through the spinal cord reveals that there is a central canal that carries cerebrospinal fluid (CSF) surrounded by grey matter on the inside, and this is surrounded by white matter. (This is the opposite to the brain’s cerebral cortex.) A section of the cord can be divided into neat symmeterical halves by the dorsal median sulcus and ventral median fissure.

The dorsal (towards the back) side of the spinal cord carries sensory information. The neurons that bring somatosensory information to the spinal cord reside in the dorsal root ganglion. Sensation from the lower body travels up the gracile tract, while sensation from the upper body and arms travels up the cuneate tract, which lies lateral to the gracile tract. There is no cuneate tract in the lumbar part of the spinal cord as sensory information from the arms does not travel through this area.

Motor information (signals coming from the brain to move the muscles) travels down the ventral (toward the front) half of the spinal cord. Motor neurons are located in the anterior (this means close to the front, in humans it means the same as ventral) horn of the grey matter. There are two main columns of neurons in the anterior horn, the medial and lateral motor columns.

The spinal cord proper ends at the level of L1. It terminates at a conical point known as the conus medullaris, from which the pia mater extends caudally as the filum terminale and attaches to the dorsal surface of the first cocygeal vertebra. After the termination of the cord, the spinal nerves continue as dangling nerves called the cauda equina (literally “horse’s tail”).

The actual cord is approxiamately cylindrical in shape, but the diameter varies at different vetebral levels. There are two enlargements, cervical and lumbar. The cervical enlargement is due to the cord segments from C5 to T1 which innervates the upper limb via the brachial plexus. The lumbar enlargement arise from segments L1 to S3 (only the region around L1/L2 is part of the spinal cord proper) and innervates the lower limbs via the lumbar and sacral plexi.

There is a higher proportion of white matter in the cervical (neck) part of the spinal cord. This is because information to and from the whole body (such as the feet) must pass through here. In contrast, the lumbar and sacral areas do not carry information from anywhere above them, so have less white matter.