IELTS Academic Reading Practice Test 182

During the opening decades of the twentieth century, parking on a public street cost nothing at all and was restricted only by the quantity of space available. As automobile ownership spread rapidly through American cities, that comfortable arrangement collapsed. Clerks and shop assistants drove to work and abandoned their vehicles at the kerb for eight or nine hours at a stretch, so that a shopper arriving at ten in the morning discovered every space within a block of the shops already occupied. Traffic circulated around the same few blocks in the hope that a gap would appear. Municipal police forces possessed no practical means of compelling a motorist to move on, because legislation said almost nothing about how long a vehicle might legitimately remain in one place.

The city that confronted the difficulty first was Oklahoma City, and the individual responsible for the solution was Carl Magee, a newspaper editor who had moved there from New Mexico. Magee chaired the traffic committee of the local chamber of commerce, and it was in that capacity that he began to consider a device which would charge a motorist for the time spent in a space and thereby persuade long-stayers to move. The concept was not entirely original, since other inventors had proposed comparable machines, but none had actually been manufactured. Magee collaborated with two engineering instructors to produce a workable model, and he applied for a patent on the mechanism.

The first meters went into service in Oklahoma City on 16 July 1935, one at each kerbside space along a downtown street, and a nickel bought an hour at the kerb. The earliest model consisted of a plain metal post with a dial on top, and local reporters, reminded of the police vehicle used to collect offenders, nicknamed it the Black Maria. The effect on the streets was immediate: within a few weeks the same spaces were turning over several times a day, and shopkeepers who had complained of being unreachable by car reported a substantial increase in custom.

Many motorists were furious, and they wrote to the newspapers arguing that the street belonged to the public and that a municipality which was obliged to keep it open could not legitimately sell the right to stop on it. In a number of towns, meters were attacked with hammers and crowbars and their dials were smashed. The legal objection was substantial enough to reach the courts, where a driver argued that the city had exceeded its powers. The judges disagreed: the purpose of the meter, they held, was to keep traffic moving rather than to raise money, and a charge designed to secure that purpose was a proper exercise of the city's authority to regulate the streets.

The mechanism of those early meters was simple and robust. A coin dropped through a slot and, in falling, wound a clockwork spring; the driver then turned a handle, and a pointer swung round the dial to indicate the hour that had been purchased. As the spring unwound, the pointer crept steadily back towards zero, and when the time expired a red flag rose into view above the case, so that a patrolling officer could see from half a block away which cars were overdue. Drivers quickly discovered that a coin tied to a length of string could be pulled back out once the spring had been wound, and that a metal washer of the correct diameter would serve quite as well as a nickel.

The idea spread with remarkable speed. By 1940 meters stood in hundreds of American cities, and manufacturers were producing them in large quantities. In Britain the first meters were installed in central London in 1958, and other European cities adopted them over the following two decades, frequently after a public argument about whether streets should remain free of charge.

Mechanical meters had disadvantages that became more conspicuous as their numbers increased. Each meter served a single space, so a city with ten thousand spaces had ten thousand locks and ten thousand coin boxes, all of which required emptying and repair. Collectors walked fixed routes carrying heavy bags of coins, and the revenue gathered was modest in relation to the labour involved. Freezing weather jammed the springs, vandals broke the dials, and the coins themselves became an increasing nuisance as the purchasing power of a nickel declined.

Electronics transformed the equipment. From the 1980s, meters with digital timers and solid-state displays replaced clockwork, and batteries or small solar panels eliminated the need for winding. The more significant change was the pay-and-display machine, which serves an entire street from one point and issues a paper ticket to be left on the dashboard. Then, in the early 2000s, cities began to accept payment by telephone: a driver registers the space and the vehicle's registration number, the money is charged to a card, and no ticket is needed, because the enforcement officer's handheld device checks a database rather than a windscreen. Sensors buried in the road surface can now report which spaces are occupied and which are vacant.

The meter has consequently become a source of data as well as of revenue. Some cities vary the charge through the day, raising it when demand is highest and lowering it during quiet periods, and drivers can consult an application that indicates where spaces are free. What has not changed is the argument for charging at all. A meter is still justified principally by turnover: it exists to ensure that the space outside a shop is used by many people for a short period rather than by one person for a whole day. The nickel has disappeared, but the underlying purpose of the device is precisely what it was in Oklahoma City in 1935.

Most large bridges are inspected by people. Engineers walk across them, examine the deck from beneath, tap concrete and photograph cracks, and in some countries a full inspection is required every two years. This approach has obvious limits. An inspector can see only the outside of a structure, and the processes that matter most — the slow growth of a crack inside a steel plate, the corrosion of a cable hidden in a duct — begin where no camera can reach. Some defects are found only when a component fails, which is far too late. Even a careful inspection records the condition of a bridge on one particular day, not a trend.

The alternative is to fit a bridge with instruments that watch it continuously. Such a network is usually called a structural health monitoring system, and its purpose is to detect change before it becomes dangerous. The most widely used device is the strain gauge, a small patch of thin metal foil bonded to a beam, or embedded in concrete when the bridge is built. When the beam is stretched or compressed, the foil changes shape and its electrical resistance changes with it. The alteration is tiny, so the gauge is connected into a circuit, the Wheatstone bridge, that turns it into a measurable voltage. A few hundred of these sensors distributed along a span can show engineers which parts of a bridge carry most load, and whether that pattern is changing.

Strain gauges measure how much a structure bends; accelerometers measure how it shakes. Modern versions are microscopic devices built on silicon chips and cost very little. Every bridge has natural frequencies at which it vibrates, determined by its mass and stiffness, and damage almost always reduces stiffness. If a girder cracks, the frequency at which the bridge sways shifts slightly, and accelerometers can detect that shift. The same instruments, fixed to the cables of a suspension bridge, record the way each cable vibrates, from which its tension can be calculated.

Fibre-optic sensors offer a different approach. A glass fibre can be run through concrete or attached along a beam, and pulses of laser light are sent down it. A section of the fibre is written with a series of microscopic gratings, a pattern known as a fibre Bragg grating, which reflects one particular wavelength of light and lets the rest pass. If the fibre is stretched by a crack opening or squeezed by a settling foundation, the spacing of the gratings changes and the reflected wavelength shifts in proportion. Because gratings can be written at intervals along a single strand, thousands of measurements can travel back through one fibre. The cable carries light rather than current, so it is immune to electrical interference and cannot cause a spark in a gas pipe.

Bridges are also monitored with instruments that sense the world around them. Anemometers on the towers record wind speed and direction, tiltmeters measure whether a pier is leaning, and thermometers show how much a structure has expanded in the sun. GPS receivers, fixed to the top of a long-span bridge, track the movement of the deck to within a few millimetres. Acoustic sensors listen for the sharp sound of a single wire snapping inside a stay cable, a failure that is invisible from outside. Engineers can also place corrosion sensors close to reinforcement and measure how quickly steel is being eaten away.

All these devices need power and a way to send their readings. Cabling a large bridge can cost more than the instruments themselves, particularly where the route crosses a river or a live railway. The answer is often a wireless network, in which small radio transmitters relay readings from node to node until they reach a base station. Power is a harder problem, and some installations now harvest it: a piezoelectric device converts the bridge's constant vibration into a trickle of electricity, and a small solar panel tops up the battery.

Monitoring has limitations that its enthusiasts sometimes underplay. A bridge moves for innocent reasons: steel expands as it warms, traffic loads come and go, and the wind pushes the whole structure sideways. These ordinary movements can be larger than the changes caused by damage, so engineers must be able to separate them, which is harder than it sounds. Sensors themselves break, and a network of hundreds will always contain a few that are reporting nonsense. The volume of data is another difficulty: a single accelerometer may produce hundreds of readings a second, and much of the art lies in deciding which of them deserve attention. Without a clear idea of what counts as a problem, a system simply generates alarms that nobody trusts.

Where monitoring is used, it tends to be on structures where the consequences of failure would be severe: long-span suspension bridges, offshore platforms and large dams. In the United States, the collapse of a highway bridge over the Mississippi River in Minneapolis in 2007, which killed thirteen people, prompted a broad review of inspection and led to more funding for monitoring research. The direction of that research is towards systems that interpret their own data. Machine learning models trained on years of readings can recognise the pattern that preceded a known defect, and detailed computer models of individual bridges can now predict how they will respond to a heavy load.

A decade ago, the advice given to anyone who complained of sleeping badly was to look at their evening habits: coffee, alcohol, late meals, exercise. Today the first question is likely to be about screens. Phones, tablets, laptops and televisions are widely presented as the principal cause of a modern epidemic of poor sleep, and the claim has the appeal of simplicity: we can all remember lying awake after a film, or waking to check a message at three in the morning. But the research behind the claim is more interesting, and more equivocal, than the headlines suggest.

The mechanism that has been studied most thoroughly is light. The body's internal clock, a cluster of cells in the brain called the suprachiasmatic nucleus, is reset every day by the light falling on the retina. A particular kind of cell in the eye, which contains a pigment called melanopsin, is especially sensitive to blue light at wavelengths of around 480 nanometres — precisely the light emitted in quantity by a backlit screen. Bright light of this kind in the evening suppresses the release of melatonin, the hormone that signals the approach of night, and pushes the clock later. In one influential experiment, volunteers read from a light-emitting e-reader for five evenings; compared with those reading a printed book, they released less melatonin, took longer to fall asleep and were less alert the following morning.

The mechanism is real, then, and the experiment was well designed. The question is how much of it applies to an ordinary evening. A phone held at arm's length delivers a small fraction of the light that reaches the eye outdoors, and most people use their devices in a room that also contains lamps. When researchers have looked at large groups of teenagers and adults, the associations between screen time and sleep are usually in the expected direction, but they are modest. Screen use, in most analyses, accounts for only a small part of the differences between one person's sleep and another's.

Part of the reason is that the arrow of causation may run the other way. A person who is anxious, or who is already sleeping badly, is more likely to be awake with a phone at midnight; the device is a symptom as much as a cause. A second complication is displacement. Time spent scrolling is time not spent asleep, and for many young people the hours lost in this way probably matter more than any hormonal response to blue light. A third mechanism is interruption: a phone that buzzes on the bedside table fragments sleep even when its owner does not consciously wake.

It is worth remembering that every new medium has been accused of damaging sleep and much else. Novels were said to keep young women awake; radio, television and video games have each been blamed in turn. Scepticism about the current panic is therefore reasonable. There is also a risk that the focus on screens distracts attention from causes that are better established and easier to fix: early school start times, which are known to cut adolescent sleep; long working hours; shift work; caffeine; and the simple fact that many families live in crowded, noisy homes.

If the aim is to help people sleep, which interventions have support? The evidence for blue-light filters is thinner than the marketing suggests: studies of 'night mode' settings find small effects on melatonin, and little or none on how long people actually sleep. Advice that does appear to help is behavioural and unglamorous — keeping the phone out of the bedroom, dimming the lights an hour before bed, and going to bed at a regular time. Yet this advice places the whole burden on the individual, and it is precisely the sort of advice that people who are exhausted and anxious find hardest to follow.

A more promising approach is to change the technology rather than scold the user. Devices already contain the tools: do-not-disturb schedules, night-time dimming, limits on notifications. What is missing is the will to switch them on by default. A phone that arrived with a bedtime mode already active, and that made it slightly awkward to disable, would probably protect more sleep than a million leaflets. The design of the services is equally important: a feed that never ends is built to be returned to, and it is unreasonable to expect willpower to defeat an engineering team.

My own view is that screens are a genuine but secondary cause of poor sleep. The clearest harm arises at the edges of the night: bright light close to the face late in the evening, and the messages that arrive once the lights are out. Both could be reduced substantially without asking anyone to give up their devices. The question we should be arguing about is not whether technology is bad for sleep, but why we have designed it to follow us into the one part of the day that ought to be free of it. That is a question about design, and about the commercial incentives that shape it, rather than about the moral character of the people who own phones.