IELTS Academic Reading Practice Test 160

Motor cars were sold for decades with nothing designed to hold their occupants in place. Early vehicles were slow, but as traffic multiplied and speeds rose, the consequences of a collision became harder to ignore. During the 1930s, surgeons in the United States began to report a pattern of injuries that they attributed to the design of car interiors: steering columns that speared drivers, metal dashboards, and passengers thrown through windscreens.

The idea of restraining a driver with a strap was not new. A two-point belt, running across the lap only, had been used in aircraft since the early years of flight, and a few American manufacturers offered lap belts as an option in the late 1940s. Such a belt stopped the body sliding forward, but it left the upper half free to rotate, and in a serious crash the wearer could fold over the strap and strike the dashboard head-first.

The solution came from an unexpected background. Nils Bohlin had spent years designing ejection seats for the Swedish aircraft maker Saab, work that taught him how the body responds to violent deceleration. In 1958 he joined Volvo and was given the task of improving the belt. His design used a single strap that ran diagonally across the chest and continued down to the hip, where it was anchored beside the seat rather than behind the occupant. The forces of a crash were shared between the pelvis, which is strong, and the ribcage, which is less so, and the body was held upright instead of being allowed to fold. The arrangement fixed the wearer at three points rather than two.

Volvo introduced the three-point belt as standard equipment in 1959, and the benefits were soon visible in Swedish hospital records. Rather than keep the design to itself, the company made the patent available to other manufacturers free of charge, a decision it has always described as being in the public interest and one that helped the three-point belt become the international standard. Within a decade most new cars in Europe were fitted with belts, though in many of them they were offered only in the front.

Persuading people to wear a belt proved harder than fitting one. Evidence accumulated through the 1960s showed that a belt was of little use if it stayed clipped to the seat. The state of Victoria in Australia became the first jurisdiction anywhere to make wearing a belt compulsory, in December 1970, and the measure was followed by a marked fall in deaths on the road. Other countries moved at different speeds: front-seat occupants in Britain were legally required to wear a belt from January 1983, while several American states resisted for years.

From 1968, federal rules in the United States required new cars to be supplied with seat belts, and engineers turned to the next problem: how to protect an occupant who had not fastened one. An inflatable cushion had been patented as early as the 1950s, but the idea was useless without a sensor able to recognise a crash in thousandths of a second. The breakthrough came from Allen Breed, who built a small device containing a steel ball held in place by a magnet; in a collision the ball was released and closed an electrical contact.

The airbag is, in effect, a small chemical factory. When a sensor reports a deceleration severe enough to suggest a serious impact, a current is passed to a detonator in the steering wheel or dashboard. The heat ignites a solid propellant, most commonly sodium azide, which burns rapidly and releases nitrogen gas. The gas fills a folded nylon bag that bursts out through a flap and is fully inflated in roughly thirty milliseconds, faster than a blink. Almost at once the bag begins to deflate through vents in its fabric, so that the occupant's head is cushioned rather than thrown back.

Airbags reached the market slowly. Mercedes-Benz offered a driver's airbag in its S-Class in 1981, and in the United States a law passed in 1991 obliged manufacturers to fit airbags to all new cars sold there by 1998. Engineers were careful to call the device a supplementary restraint system, because it was never meant to replace the belt. A belt holds an occupant in the right position and absorbs energy over a distance; an airbag spreads the load of a head or chest across a larger area. Used together, the two work far better than either alone.

Early airbags also caused harm. Because they were designed to protect an unbelted adult male, they inflated with considerable force, and in the United States a number of small adults and children were killed by bags that deployed while their faces were close to the dashboard. Children in rear-facing seats were especially at risk, since the bag struck the back of the seat where the child's head rested. From the late 1990s manufacturers fitted less powerful inflators, and cars acquired sensors that adjusted deployment to the weight and position of the person in the seat.

A more recent scandal has raised different questions. From 2013, a series of recalls affected airbag inflators made by the Japanese supplier Takata, whose propellant used ammonium nitrate. In humid conditions the chemical could deteriorate and burn too fiercely, rupturing the metal housing and throwing fragments into the cabin. The recalls eventually covered tens of millions of vehicles and several manufacturers, making them one of the largest safety campaigns in the history of the industry. Both devices continue to develop, with better side cushions and reminders for rear-seat passengers now required in some markets.

Aviation produces a small but growing share of global carbon emissions, generally estimated at two to three per cent of the total from human activity, and its effect on the climate is larger than that figure implies, because aircraft also release nitrogen oxides and leave condensation trails at high altitude. Kerosene has no practical low-carbon substitute for long flights, and passenger numbers keep rising. Small electric aircraft, carrying two to nine people a few hundred kilometres, are the first serious attempt to move part of aviation off fossil fuel.

The obstacle is weight. A kilogram of jet fuel contains roughly forty-three megajoules of energy; a kilogram of the best lithium-ion battery available today holds less than one. Worse, an aircraft burns fuel as it flies and lands much lighter than it took off, whereas a battery weighs exactly the same at the end of a flight as at the beginning. Every kilogram of battery carried is a kilogram of payload or range that must be given up, and the penalty compounds: a heavier airframe needs more power, which needs more battery.

Electric propulsion has compensating advantages. A motor converts well over ninety per cent of the electricity it receives into turning force, while a small gas turbine at best manages around forty per cent of the energy in its fuel, the rest leaving as heat in the exhaust. Motors are also far quieter, need much less maintenance, and can be placed in unusual positions on an airframe, since they require neither fuel lines nor exhaust ducts. Distributed propulsion — several small propellers along a wing, driven by one power source — may allow designers to shape the airflow and reduce drag.

The first electric aircraft to be certificated for commercial use was a two-seat trainer. The Velis Electro, built by the Slovenian company Pipistrel, received type certification from the European Union Aviation Safety Agency in June 2020 and is now used by flying schools. Its battery allows a flight of under an hour with a reserve, which is enough for a lesson but little else. The aircraft is quiet enough to be flown from small airfields near towns, and its running costs per hour are low.

Larger designs are following. In September 2022 a nine-seat prototype called Alice, built by the company Eviation, took off from an airfield at Moses Lake in the state of Washington and flew for about eight minutes. The aircraft is intended to carry passengers on short regional routes, and the design has attracted interest from airlines and parcel carriers. Its shape is unusual, with two propellers at the rear and one at each wingtip, and its battery pack accounts for a large fraction of its weight — a fraction the company is trying to reduce by improving the cells rather than the motors.

Two other approaches avoid the all-electric dead end. A hybrid aircraft can carry a fuel-burning engine that drives a generator, with electric motors turning the propellers; the engine then runs at its most efficient speed, and the aircraft burns less fuel than a conventional turboprop of the same size. Alternatively, hydrogen can be fed to a fuel cell, which produces electricity and emits only water. In January 2023 a modified nineteen-seat Dornier 228 flew in England with one of its two engines replaced by a hydrogen-electric unit. Hydrogen is light but bulky, and storing it as a liquid requires very low temperatures.

Ground infrastructure is a constraint in its own right. A regional aircraft on a busy schedule may have twenty minutes between flights, and charging a large battery in that time demands a supply of several megawatts, comparable to that of a small factory. Airports would need new cabling, transformers and stands, and the local grid may not cope. One proposed solution is to remove the depleted pack and slide in a charged one, but swapping a pack that weighs a tonne requires machinery that few airfields possess.

For all these reasons, few engineers expect electric aircraft to replace long-haul jets. The energy needed to lift a wide-body aircraft across an ocean is simply too great. The realistic market is the one that regional turboprops and training aircraft serve today: journeys of a few hundred kilometres, in which the aircraft spends much of its time climbing and descending, the phases in which electric motors are at their most efficient. Many of the world's flights are short enough to fall within this range, and replacing even a fraction of them would improve air quality around the airports that people live beside.

Batteries are improving steadily, though not as fast as enthusiasts once hoped. Solid-state cells, which replace the liquid electrolyte with a solid material, promise a higher energy density and a smaller risk of fire, and several manufacturers expect to produce them for vehicles within a decade. Lithium-sulphur chemistries are at an earlier stage. Certification, however, is slow: every new cell chemistry must be shown to behave predictably when damaged, overcharged or punctured, and the standards for aviation batteries are stricter than those for cars.

The lesson of the past decade is that electric flight is neither a fantasy nor an imminent upheaval. It works, in a narrow set of roles, with today's batteries. Whether it expands beyond them depends less on the motors, which are already excellent, than on the chemistry of the cells that supply them.

Walk into almost any large supermarket and you will be met by a row of machines where a line of cashiers used to stand. The self-service checkout promised to shorten queues, cut costs and give shoppers control of their own purchases. It has done some of these things, in some shops, for some people. But the debate about the machines has been conducted largely in the language of efficiency, as though the only questions that mattered were how many items a minute could be processed and how many hours of staff time could be saved. Those are not the only questions, and the arguments on both sides deserve more attention than they usually receive.

The technology is older than most shoppers realise. The first self-checkout lanes were installed in a supermarket in Atlanta, Georgia, in the mid-1980s, and for the next fifteen years the machines remained a curiosity, expensive and unreliable. They spread in the 2000s, when supermarkets were looking for ways to reduce the number of staffed tills at busy times without losing sales. A single assistant could watch over six machines, and lanes could be added at peak hours without recruiting anyone. The appeal to retailers was never really about the shopper's experience; it was about the wage bill.

There is a case for the machines, and it should be stated fairly. They take up less space than a staffed till, they can be open when no cashier is available, and they suit customers buying a handful of items who do not want to wait behind a full trolley. For some people they offer privacy: a shopper buying medicine or a personal item may prefer not to hand it to another person. And the labour saved is real, if smaller than the early claims suggested, because every machine needs an assistant to authorise age-restricted sales, clear errors and sort out the payment terminal.

The trouble is that the machines fail often, and each failure is expensive in exactly the currency they were meant to save: time. A customer who puts an item in the bagging area, or who uses their own bag, may trigger a warning that only a member of staff can clear. With one assistant responsible for six or eight tills, a single problem can halt a line for several minutes while shoppers wait, and the queue that forms is no shorter than the one at a staffed till. The machine has not removed the human being from the transaction; it has moved them further away.

Losses are a second concern. Studies of retail shrinkage — the difference between the stock a shop records and the stock it actually has — have repeatedly found higher rates at self-service tills than at staffed ones, and the reasons are mixed. Some of the loss is simple error: customers scan one item twice, or leave something in the trolley. Some is deliberate, and the opportunity is obvious, since nobody is watching what goes into the bag. Whether mistakes or theft account for the larger share is not known, and retailers have responded by adding cameras, weighing scales and random checks, all of which slow the process down.

Then there is the question of work. Cashiers were not made redundant in the numbers that were once predicted, but their jobs changed: the same people now stand behind a bank of machines, resetting them and apologising. That is not nothing, but neither is it the same job, and the training and status attached to it are different. What has gone altogether, in many stores, is the brief exchange at the till — the remark about the weather, the recognition of a regular customer. For some shoppers, particularly those who live alone, that exchange was the only conversation of the day.

Some retailers have begun to reconsider. In 2023 the northern English chain Booths announced that it would remove self-checkouts from most of its stores, saying that customers had told them the machines were slower and less friendly than a person. Several other companies have reduced the number of machines in stores where they were unpopular. These decisions are often reported as a verdict on the technology itself, which they are not: they are evidence that shoppers value being able to choose.

My own view is that the machines are neither the villain nor the saviour of the supermarket. Used where they make sense — a small basket, a quick purchase, a shop that would otherwise be closed — they are genuinely convenient. The mistake was to treat them as a universal replacement, installing them in every store and reducing staffed tills to one or two, so that a shopper with a full trolley, a question about a product or a need for help now has no alternative. A technology that is imposed rather than offered will always be resented, however well it works.

The sensible policy is therefore not removal but restraint. Supermarkets should keep staffed tills open alongside the machines, design the machines so that disabled shoppers can use them without assistance, and stop using them to disguise cuts in staffing. The question worth asking about any labour-saving device is not whether it can replace a person, but whether the service it provides is better, worse or merely cheaper. On that test, the self-service checkout has some way to go.