The Future Of Traffic Tracking

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Future Traffic Tracking

You are in a shrinking minority of the American population if you don’t own at least one electronic communications device. There are more than 119 million cell-phone users in the United States as of July 2001. Each day, thousands more sign up. Millions more have two-way pagers. The radio signals emitted from these devices can reveal our location at anytime. This ability to locate cell-phone users will become a vital component of future traffic-management systems.

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On a short stretch of highway in Calgary, Alberta, Cell-Loc is testing out its new cell-phone tracking technology. In July 2001, the company sent a known vehicle down a 1.25-mile (2-km) section of a major highway, through the heart of the town, to test the accuracy of its system. The truck carried a GPS receiver onboard to compare the system’s accuracy.

“We collected data from both the GPS receiver in the vehicle, and from our system that was monitoring the cell phone remotely, and we compared the two and found them to be, not identical, but close enough for our applications we’re talking about,” Andrew Hillson, Cell-Loc’s director of service technology, said.

Here’s how the Cellocate system will work, according to Hillson and company documents:

  • Listening posts are placed throughout a city, either next to a cell-phone base station or in independent locations. Listening posts are comparable to half a base station: They can detect but not transmit radio signals.
  • Three listening posts are needed to get a two-dimensional position of a cell-phone user.
  • Listening posts detect cell-phone transmission, decode it and then time-stamp the arrival of a wavefront from the transmission.
  • Once three towers have time-stamped a transmission, the information is quickly sent to a central computer that uses hyperbolic multilateration to determine the cell phone’s position on a highway.

“Hyperbolic multilateration” is just a fancy way of saying triangulation, Hillson said. A position is determined by locating the intersection of the hyperbolas from the radio waves detected by the listening posts. By analyzing how long it takes the radio wave to reach the listening post from the cell phone, a computer can calculate almost precisely where someone is located on the highway. If the person’s location on the map is shown as off the highway, the computer corrects for this and snaps the location to the road. The entire process of detecting a person’s position occurs in seconds.

Hillson said that Cellocate meets the FCC’s mandate and is accurate within 330 feet (100 m) 67 percent of the time. Within 990 feet (300 m), the system is accurate 95 percent of the time. It supports AMPS(Advanced Mobile Phone System) and CDMA (Code Division Multiple Access) air interfaces. Cell-Loc is pursuing partnerships with cell-phone service providers. The service, which would allow cell-phone users to receive instant, personalized traffic warnings, will likely be available in a year or two and cost about $4 or $5 per month.

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Intelligent Traffic Signals

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How does a traffic light detect that a car has pulled up and is waiting for the light to change?

There is something exotic about the traffic lights that “know” you are there — the instant you pull up, they change! How do they detect your presence?

Some lights don’t have any sort of detectors. For example, in a large city, the traffic lights may simply operate on timers — no matter what time of day it is, there is going to be a lot of traffic. In the suburbs and on country roads, however, detectors are common. They may detect when a car arrives at an intersection, when too many cars are stacked up at an intersection (to control the length of the light), or when cars have entered a turn lane (in order to activate the arrow light).

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There are all sorts of technologies for detecting cars — everything from lasers to rubber hoses filled with air! By far the most common technique is the inductive loop. An inductive loop is simply a coil of wire embedded in the road’s surface. To install the loop, they lay the asphalt and then come back and cut a groove in the asphalt with a saw. The wire is placed in the groove and sealed with a rubbery compound. You can often see these big rectangular loops cut in the pavement because the compound is obvious.

Inductive loops work by detecting a change of inductance. To understand the process, let’s first look at what inductance is. The illustration on this page is helpful.

What you see here is a battery, a light bulb, a coil of wire around a piece of iron (yellow), and a switch. The coil of wire is an inductor. If you have read How Electromagnets Work, you will also recognize that the inductor is an electromagnet.

If you were to take the inductor out of this circuit, then what you have is a normal flashlight. You close the switch and the bulb lights up. With the inductor in the circuit as shown, the behavior is completely different. The light bulb is a resistor (the resistance creates heat to make the filament in the bulb glow). The wire in the coil has much lower resistance (it’s just wire), so what you would expect when you turn on the switch is for the bulb to glow very dimly. Most of the current should follow the low-resistance path through the loop. What happens instead is that when you close the switch, the bulb burns brightly and then gets dimmer. When you open the switch, the bulb burns very brightly and then quickly goes out.

The reason for this strange behavior is the inductor. When current first starts flowing in the coil, the coil wants to build up a magnetic field. While the field is building, the coil inhibits the flow of current. Once the field is built, then current can flow normally through the wire. When the switch gets opened, the magnetic field around the coil keeps current flowing in the coil until the field collapses. This current keeps the bulb lit for a period of time even though the switch is open.

The capacity of an inductor is controlled by two factors:

  • The number of coils
  • The material that the coils are wrapped around (the core)

Putting iron in the core of an inductor gives it much more inductance than air or any other non-magnetic core would. There are devices that can measure the inductance of a coil, and the standard unit of measure is the henry.

So… Let’s say you take a coil of wire perhaps 5 feet in diameter, containing five or six loops of wire. You cut some grooves in a road and place the coil in the grooves. You attach an inductance meter to the coil and see what the inductance of the coil is. Now you park a car over the coil and check the inductance again. The inductance will be much larger because of the large steel object positioned in the loop’s magnetic field. The car parked over the coil is acting like the core of the inductor, and its presence changes the inductance of the coil.

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Happy new year……………

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Happy new year to you all……….

Dans le Townhouse_Happy New Year

How Intelligent Highways Will Work

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Intelligent Highways 

The main artery for travelling in and out of Toronto, Ontario, is Highway 401, a thoroughfare that expands to 12 to 14 lanes at its widest. And at over 350,000 vehicles per day, including 45,000 trucks, Highway 401 is exceeded in terms of traffic volume only by the Santa Monica freeway in Los Angeles. “It’s world-class congestion. It comes to a grinding halt at rush hour virtually every day,” Brian Marshall, of the Canada Transportation Development Centre, said.

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Traffic is a growing problem in almost every city in the world. The average American motorist spends 36 hours in traffic delays every year. The cost of traffic congestion just in the United States is $78 billion, representing the 4.5 billion hours of travel time and 6.8 billion gallons of fuel wasted sitting in traffic. Billions more dollars have been spent on electronics and systems to alleviate this logjam.

Government transportation agencies are seeking out new, cheaper technology to replace the high-priced loop sensors and other invasive technologies that have been used in the past. In this article, we will drive on the freeway of the future and see how ubiquitous digital devices will aid in easing our traffic woes

Current Traffic Tracking

The next time you are driving to work, take a minute to look at the technology in place to keep traffic flowing. Over the past two decades, state departments of transportation have installed billions of dollars worth of electronics to keep an eye on and manage traffic.

Here are the three basic devices used in managing traffic today:

  • Loop detectors
  • Video cameras
  • Electronic display signs

Loop detectors are wires embedded in the road that detect small changes in electrical voltage caused by a passing vehicle. Traffic speed can be determined by detecting how quickly cars pass between two sets of loop detectors. Volume and speed data is transmitted to a central computer, which is monitored by local transportation departments.

If the detectors sense a slowdown or an increased quantity in traffic, workers can use video cameras to get a better understanding of what’s causing it. Meanwhile, messages can be displayed on electronic signs to warn motorists of congestion ahead and to advise of alternate routes.

“The traditional loops in the road and cameras up on poles and guys sitting behind desks looking at monitors is too expensive to extend as far as people would like,” Marshall said. Installing these detectors, cameras and signs has been a long process to complete, and is costing billions of dollars for state and federal governments to implement. Transportation officials are now searching for cheaper alternatives for managing traffic.

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Destroyer of Bridges

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Weather, Destroyer of Bridges

While wind can certainly induce destructive resonant waves, weather as a whole unleashes a host of destructive assaults on the bridges we build. In fact, the relentless work of rain, ice, wind and salt will inevitably bring down any bridge that humans can erect.

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Bridge designers have learned their craft by studying the failures of the past. Iron has replaced wood, and steel has replaced iron. Prestressed concrete now plays a vital role in the construction of highway bridges. Each new material or design technique builds off the lessons of the past. Torsion, resonance and poor aerodynamic designs have all led to bridge failures, but engineers continually bounce back with innovations to solve design problems.

Weather, however, is a patient and unpredictable adversary. Cases of weather-related bridge failure tend to outnumber those of design-related failures. This trend can only suggest that we have yet to come up with an effective solution. To this day, no specific construction material or bridge design can eliminate or even mitigate these forces. After all, we’re talking about the same forces that degrade whole mountain ranges and forge deep chasms in the earth. By comparison, a man-made bridge is nothing.

As with the ancient Incan suspension bridges, the only deterrent is continual preventive maintenance.

Resonance

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More Bridge Forces: Resonance

You can think of resonance as the vibrational equivalence of a snowball rolling down a hill and becoming an avalanche. It begins as a relatively small, periodic stimulus of a mechanical system, such as wind buffeting a bridge. These vibrations, however, are more or less in harmony with the bridge’s natural vibrations. If unchecked, the vibration can increase drastically, sending destructive, resonant vibrations traveling through a bridge in the form of torsional waves.

The most noteworthy example of resonance occurred in 1940, when resonant vibrations destroyed the Tacoma Narrows Bridge in Washington. The incident was especially shocking at the time as the structure was designed to withstand winds of up to 120 miles (193 kilometers) per hour and collapsed in a mere 40-mile (64-kilometer) wind.

bridge

Close examination of the situation suggested that the bridge’s deck-stiffening truss was insufficient for the span, but this alone couldn’t bring such a structure down. As it turned out, the wind that day was at just the right speed and hit the bridge at just the right angle to set off the deadly vibration. Continued winds increased the vibrations until the waves grew so large and violent that they broke the bridge apart. The effect is similar to that of a singer shattering a glass with her voice.

Wind isn’t the only potential threat, however. When an army marches across a bridge, the soldiers often “break step” so that their rhythmic marching will start resonating throughout the bridge. A sufficiently large army marching at just the right cadence could set the deadly vibration into motion.

In order to mitigate fully the resonance effect in a bridge, engineers incorporate dampeners into the bridge design to interrupt the resonant waves and prevent them from growing.

Another way to halt resonance is to give it less room to run wild. If a bridge boasts a solid roadway, then a resonant wave can easily travel the length of the bridge and wreak havoc. But if a bridge roadway is made up of different sections with overlapping plates, then the movement of one section merely transfers to another via the plates, generating friction. The trick is to create enough friction to change the frequency of the resonant wave. Changing the frequency prevents the wave from building.

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The Living Bridges

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The Living Bridges

While the first bridges were likely nothing short of logs toppled over creeks, most of humanity’s bridge-building legacy is a story of artificial structures crafted out of the elements. We can find, however, one of the most striking exceptions to this rule in the Meghalaya region of northern India.

wood bridge

During monsoon season, locals here endure some of the wettest conditions on Earth, and rising floodwater’s cut the land into isolated fragments. Build a bridge out of woven vines or hewn boards and the rain forest moisture will inevitably turn it into compost. As you can see from the photo, the local people developed a rather elegant solution to the problem: They grow their bridges out of natural vegetation. In doing so, they turn a large portion of the bridge maintenance duties over to the bridge itself.

Building a living bridge takes patience, of course. The local villagers plan their constructions a decade or more in advance. The War-Khakis people, for instance, create root-guidance systems from the hollowed halves of old betel nut tree trunks to direct strangler fig roots in the desired direction. They simply direct the roots out over a creek or river, spanning it, and only allow the roots to dive into the earth on the opposite bank. The larger living bridges boast lengths of up to 100 feet (30 meters), can bear the weight of 50 people and can last upward of 500 years

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But the weight of car or foot traffic is far from the only force affecting a bridge.

Additional Bridge Forces: Torsion and Shear

So far, we’ve touched on the two most important forces in bridge design: compression and tension. Yet dozens of additional forces also affect the way bridges work. These forces are usually specific to a particular location or design.

Torsion, for instance, is a particular concern for engineers designing suspension bridges. It occurs when high wind causes the suspended roadway to rotate and twist like a rolling wave. As we’ll explore on the next page, Washington’s Tacoma Narrows Bridge sustained damage from torsion, which was, in turn, caused by another powerful physical force

The natural shape of arch bridges and the truss structure on beam bridges protects them from this force. Suspension bridge engineers, on the other hand, have turned to deck-stiffening trusses that, as in the case of beam bridges, effectively eliminate the effects of torsion.

In suspension bridges of extreme length, however, the deck truss alone isn’t enough protection. Engineers conduct wind tunnel tests on models to determine the bridge’s resistance to torsional movements. Armed with this data, they employ aerodynamic truss structures and diagonal suspender cables to mitigate the effects of torsion.

Shear: Shear stress occurs when two fastened structures (or two parts of a single structure) are forced in opposite directions. If left unchecked, the shear force can literally rip bridge materials in half. A simple example of shear force would be to drive a long stake halfway into the ground and then apply lateral force against the side of the upper portion of the stake. With sufficient pressure, you’d be able to snap the stake in half. This is shear force in action.

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Cable-Stayed Bridge

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At first glance, the cable-stayed bridge may look like just a variant of the suspension bridge, but don’t let their similar towers and hanging roadways fool you. Cable-stayed bridges differ from their suspension predecessors in that they don’t require anchorages, nor do they need two towers. Instead, the cables run from the roadway up to a single tower that alone bears the weight.

cable bridge

The tower of a cable-stayed bridge is responsible for absorbing and dealing with compression forces. The cables attach to the roadway in various ways. For example, in a radial pattern, cables extend from several points on the road to a single point at the tower, like numerous fishing lines attached to a single pole. In a parallel pattern, the cables attach to both the roadway and the tower at several separate points.

Engineers constructed the first cable-stayed bridges in Europe following the close of World War II, but the basic design dates back to the 16th century and Croatian inventor Faust Vrancic. A contemporary of astronomers Tycho Brache and Johannes Kepler, Vrancic produced the first known sketch of a cable-stayed bridge in his book “Machinae Novae.”

Today, cable-stayed bridges are a popular choice as they offer all the advantages of a suspension bridge but at a lesser cost for spans of 500 to 2,800 feet (152 to 853 meters). They require less steel cable, are faster to build and incorporate more precast concrete sections.

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Not all bridges require great hunks of steel and concrete though. Sometimes a tree root or two will do the trick.

The Suspension Bridge

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As the name implies, suspension bridges, like the Golden Gate Bridge or Brooklyn Bridge, suspend the roadway by cables, ropes or chains from two tall towers. These towers support the majority of the weight as compression pushes down on the suspension bridge’s deck and then travels up the cables, ropes or chains to transfer compression to the towers. The towers then dissipate the compression directly into the earth.

The supporting cables, on the other hand, receive the bridge’s tension forces. These cables run horizontally between the two far-flung anchorages. Bridge anchorages are essentially solid rock or massive concrete blocks in which the bridge is grounded. Tensional force passes to the anchorages and into the ground.

The InfoVisual.info site uses images to explain objects.

In addition to the cables, almost all suspension bridges feature a supporting truss system beneath the bridge deck called a deck truss. This helps to stiffen the deck and reduce the tendency of the roadway to sway and ripple.

Suspension bridges can easily cross distances between 2,000 and 7,000 feet (610 and 2,134 meters), enabling them to span distances beyond the scope of other bridge designs. Given the complexity of their design and the materials needed to build them, however, they’re often the most costly bridge option as well.

But not every suspension bridge is an engineering marvel of modern steel. In fact, the earliest ones were made of twisted grass. When Spanish conquistadors made their way into Peru in 1532, they discovered anIncan empire connected by hundreds of suspension bridges, achieving spans of more than 150 feet (46 meters) across deep mountain gorges. Europe, on the other hand, wouldn’t see its first suspension bridge until nearly 300 years later.

Of course, suspension bridges made from twisted grass don’t last that long, requiring continual replacement to ensure safe travel across the gap. Today, only one such bridge remains, measuring 90 feet (27 meters) in the Andes.

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The Arch Bridge

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After more than 2,000 years of architectural use, the arch continues to feature prominently in bridge designs and with good reason: Its semicircular structure elegantly distributes compression through its entire form and diverts weight onto its two abutments, the components of the bridge that directly take on pressure.

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Tensional force in arch bridges, on the other hand is virtually negligible. The natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch.

But as with beams and trusses, even the mighty arch can’t outrun physics forever. The greater the degree of curvature (the larger the semicircle of the arch), the greater the effects of tension on the underside of the bridge. Build a big enough arch, and tension will eventually overtake the support structure’s natural strength.

While there’s a fair amount of cosmetic variety in arch bridge construction, the basic structure doesn’t change. There are, for example, Roman, Baroque and Renaissance arches, all of which are architecturally different but structurally the same.

It is the arch itself that gives its namesake bridge its strength. In fact, an arch made of stone doesn’t even need mortar. The ancient Romans built arch bridges and aqueducts that are still standing today. The tricky part, however is building the arch, as the two converging parts of the structure have no structural integrity until they meet in the middle. As such, additional scaffolding or support systems are typically needed.

Modern materials such as steel and prestressed concrete allow us to build far larger arches than the ancient Romans did. Modern arches typically span between 200 and 800 feet (61 and 244 meters), but West Virginia’s New River Gorge Bridge measures an impressive 1,700 feet (518 meters)

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