A Field Guide to Roadside Technologyby Ed Sobey
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This fascinating handbook answers the questions of anyone who has ever wondered about the many strange devices found along the roadside, from utility poles to satellite dishes. Devices are grouped according to their habitatsalong highways and roads, atop buildings, near airports, and on utility towers. More than 150 different roadside technologies are covered, and each detailed entry describes what the device does, how it works, and also includes a photograph for easy identification. With helpful sidebars describing related technical issues such as why stoplights are constructed with the red light on top, this handbook for curious readers provides carefully detailed descriptions and the history behind many of the devices that roadside travelers take for granted.
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A Field Guide to Roadside Technology
By Ed Sobey
Chicago Review Press IncorporatedCopyright © 2006 Ed Sobey
All rights reserved.
HIGHWAYS AND ROADWAYS
HIGHWAYS AND ROADWAYS ARE technology showcases zipping past your car window as you travel along at 60 MPH (100 KM/H). Every few seconds you whiz by yet another piece of machinery. Luckily, the same type of device is often found at every intersection or every few miles, so you have many opportunities to see and identify each one.
Since state and local governments maintain their own roads and highways, many of the devices you see aren't uniform across the country. Highway devices in California may not look exactly like similar devices in Massachusetts. However, if you can identify a machine in one location, you will have clues as to what a device of similar size and shape does in a different location, even if it isn't exactly the same.
Controls traffic by indicating which lane of cars should move through the intersection.
At busy intersections.
HOW IT WORKS
Watch a traffic signal and you'll figure out that it uses a timer. The light stays green for maybe 30 seconds, turns yellow for 5 or so seconds, then turns red for perhaps 35 seconds while the green and yellow lights for the other lanes of traffic complete their cycles.
Traffic engineers set the times for each part of the cycle based on the traffic load on each street. They may also change the cycle to run faster at night when there are fewer cars on the road. Many traffic signals are also controlled by switches (see below).
Does the red light look different from the yellow and green lights? Instead of using normal incandescent light bulbs (like the ones you use at home) for red lights, many cities now use LEDs, or light-emitting diodes. LEDs have a deeper color than incandescent bulbs. You can see the many sources of light, which are the individual diodes. It takes dozens of tiny LEDs to make up one red traffic light.
LEDs are much more expensive than regular lights. Why would traffic departments switch to a more expensive light? LEDs can last as long as 10 years — several times longer than traditional lights. The expense of sending a crew out to change a traffic light bulb is so great that it's cheaper to use a more expensive light source that lasts longer. Lighting engineers just recently developed good yellow and green LEDs, and traffic departments are starting to install those colors now.
If you see a traffic signal that uses incandescent bulbs open for repair, look inside to see what color the bulbs are. They might not be red, green, and yellow. Some cities use a yellow bulb shining through a blue cover to make a green light.
Increasingly, engineers are installing additional devices called switches to control the lights as well. At an intersection, look for dark lines in the shape of a square or rectangle in the road's surface. The dark lines are patched strips in the road where workers sawed up the original roadway to install an induction vehicle detector (see page 19), which consists of loops, or coils, of wire that detect cars and change traffic lights accordingly.
At some intersections you'll see other devices that prompt traffic lights to change. These include video detection cameras (see page 20) and microwave vehicle detectors(see page 20), which are mounted on traffic poles.
Old traffic signals use mechanical systems to turn each light on and off. You can hear the motors and switches inside these signals working as the lights change.
Modern traffic signals use electronic circuits instead of mechanical systems to control the lights. The next time you're stopped at one of these, look for the traffic signal control box (see page 18), which houses the signal's timer, or clock, and switches. It may be mounted on one of the traffic-signal poles or placed on the ground behind the signal.
Traffic lights were used even before automobiles were invented. Starting in 1868, the British used red and green lights to control horse carriage traffic at busy intersections. A police officer had to manually switch the lights from red to green and back. The use of a yellow light also originated in Great Britain, in 1918.
The first red and green traffic lights in America appeared in Cleveland, Ohio, in 1914. A police officer, William Potts, created the first three-color light used in the United States and had it installed in Detroit in 1920. Three years later the famous inventor Garrett Augustus Morgan invented the automatic traffic light.
Traffic Signal Control Box
Houses electronic circuits and power supplies that control traffic lights.
At any intersection where you find a modern traffic signal you will find one or two control boxes, usually on one of the corners of the intersection. Often, as is the case shown here, you will see two boxes. One houses the electronic circuits and the other houses power supplies for the traffic signal.
HOW IT WORKS
One box (shown on the left in this photo) controls the signals. Inside it is a computer. The computer can be set to change the traffic lights at set time periods. For example, it may be set to cycle through the green, yellow, and red lights every 30 seconds. The timing can be set to change throughout the day to accommodate changes in traffic patterns. Traffic engineers study the flow of traffic and program a computer to run the lights accordingly.
If there is an induction vehicle detector (see page 19) at the intersection, its signals go into the control computer as well. As a car pulls up to the intersection and stops above the detector's wire ground loop, the sensor (loop) sends a message to the computer, which prompts the traffic light to change.
The second box distributes power to the computer and the traffic signal. Electrical power comes into this box from electric wires located on utility poles or underground. Inside this box are the connections.
Induction Vehicle Detector
When a vehicle moves over the detector, the detector sends a message to the traffic signal's computer to start the cycle to change the lights.
Busy intersections. Look on the ground for a thin bead of black asphalt that covers up the square or rectangle of wire that was installed after the road was last paved.
HOW IT WORKS
This operates in the same way as do the metal detectors you see people using at the beach or in a park. An electric current flows through the coil of wires under the street. As a car moves over the coil, the car's metal changes the magnetic field in the coil. A sensor in the circuit of the coil detects the change in the magnetic field and sends a signal to the computer in the control box.
Some cities mark the place in the road that covers the most sensitive area of the coil with an "X" so people riding bicycles know where to stop. Since bikes have much less metal than cars, the detector might not notice the change in the magnetic field caused by the bike unless it is placed directly over the most sensitive area of the coil. The mark shows where the bicyclists should stop to change the signal.
The wire coils are set about two inches below the top of the road's surface. Workers use a rotary saw to cut grooves in the road. Then they place the wire in the grooves and seal the wires into the road with hot asphalt, which is the dark line you see.
Video Detection Camera
Detects cars stopped at an intersection and sends a message to the traffic signal's computer to begin the cycle of light changes.
This camera takes the place of an induction vehicle detector (see page 19), which uses magnetic loops buried in the road. The advantages of a video detection camera over an induction vehicle detector are twofold: engineers can set the camera in place quickly, and they do not have to disrupt traffic by digging up the road to install loops.
At intersections, directly above the arm that supports a traffic signal. You can distinguish it from a traffic surveillance camera (see page 23) in two ways. First, it is mounted on a shorter arm or pole than is a surveillance camera. Second, it is fixed in place — it has no motor to move it, so it can't pan (turn sideways) or tilt (move up and down).
HOW IT WORKS
A computer monitors certain points within the image picked up by the camera's field of view. When most or all of those points change (because a car comes into the view), the computer sends a message to the traffic signal's computer to change the light.
Optical sensing technology is improving quickly; look for this device to replace the induction vehicle detector in the near future.
Microwave Vehicle Detector
Uses microwaves (radar) to detect vehicles at an intersection so it can trigger the traffic signal's computer to change the lights.
Permanent installations and temporary installations where induction vehicle detectors have been dug up. Most often these are dug up to repair the road surface. It is mounted on a signal arm (a pipe that supports a traffic signal over the road).
HOW IT WORKS
The microwave vehicle detector sends out a radar beam. When the beam bounces off a car the reflected signal is detected and trips a switch in the detector, which sends a message to the traffic signal's computer to change the light.
The detector is about six inches (15 cm) long and four inches (10 cm) high. The front is covered with black film that keeps out light (and dirt) while allowing microwaves to pass through.
Emergency Preemption Detector
Controls traffic signals so emergency vehicles can get through intersections faster.
Located above the lanes of traffic, on top of the support arms that hold up traffic lights.
HOW IT WORKS
Emergency vehicles have flashing (strobe) lights that activate the detector. The lights may be either visible or infrared. Infrared light has wavelengths too long for human eyes to see.
Typically a detector is set to respond to strobe lights when they first appear about 1,000 feet (300 m) from the intersection. This gives time for the signal light to change and for cars ahead of the emergency vehicle to move through the intersection and out of the way.
Some cities' emergency preemption detectors have two levels of operation. One level, High Priority, is for emergency vehicles; the other, Low Priority, is for buses.
Look for the distinctive shape on top of traffic light arms. The detector is taller than it is wide, is dark in color, and typically has two shields that project outward, like the bills of two baseball hats, one above the other.
Traffic Surveillance Camera
Videotapes traffic so engineers can improve traffic flow by making changes to signals and signage.
Along major highways and at busy intersections. The camera is mounted on a tall pole or a long arm that extends above a traffic signal. Engineers set the camera up high so it can capture a wide field of vision.
HOW IT WORKS
The video recorded by this type of camera may be no match for The Simpsons in terms of entertainment value, but a traffic surveillance camera does capture important information. By examining the recording via monitors, engineers can study the movement of cars and determine how they should change the timing of traffic signals.
Engineers can tilt the camera up and down and pan it left and right to see traffic in all directions. No one sits at the monitors watching traffic all day, so if you make faces at the camera it's likely that no one will see you. But when a problem arises, the engineers can look to see what's happening and can record the scenes on magnetic tape.
In some areas, engineers have turned traffic surveillance cameras into Web cams that allow people to check for traffic backups via the Internet. To see traffic conditions around Seattle, for example, viewers can check the Washington State Department of Transportation's Web site (www.wsdot.wa.gov/traffic/seattle), which offers links to several such Web cams. California's Caltrans Web site (http://video.dot.ca.gov) offers viewers access to live feed from hundreds of cameras monitoring sections of freeways throughout the state, and the New York City Department of Transportation offers traffic-surveillance Web cams at its Advanced Traveler Information System Web site (http://nyctmc.org/). Those interested in seeing what traffic's like in Philadelphia can log onto http://Philadelphia.pahighways.com/expressways. For a comprehensive array of links to traffic-surveillance Web cams in major cities throughout the United States, check out the Where in Federal Contracting? Web site (www.wifcon.com/gettingsummeruscities.htm).
Records the number of vehicles using the road via rubber hoses. Traffic engineers use this data to determine if there is too much traffic for the road to handle.
On any road except a high-speed highway.
HOW IT WORKS
Rubber hoses are laid across a road. These are attached to the counter, a device housed in a metal box that is placed alongside the road. As cars, trucks, and even bicycles cross the rubber hoses, they compress the hoses, sending blasts of air into the counter. The air moves a diaphragm that is connected to a switch. The switch then sends an electrical signal to circuits inside the counter that record the traffic count.
Typically a counter has two hoses. One hose stretches across the entire road and the other reaches only the center of the road. The counts from the two hoses are recorded separately. The count for one direction of traffic is taken from the short hose. The count for the other direction of traffic is obtained by subtracting the count produced by the shorter hose from the count produced by the longer hose. Each count is divided by two (because the average vehicle has two axles) to determine the approximate number of vehicles traveling in a particular direction on that road.
Engineers also use traffic counters to calculate vehicle speeds. The counters record the length of time that passes between the moment that a vehicle's front tires depress the hose and the moment that its rear tires depress it. Traffic counters aren't used as a way to catch and issue tickets to speeding drivers, but the vehicle-speed information they record is used to determine if there is a need to post speed-limit signs or other signs designed to slow traffic.
Audible Crossing Signal
Allows blind people to cross intersections safely by audibly indicating when they have the green light to cross.
In many cities, at intersections that feature traffic signals for pedestrians as well as vehicles.
HOW IT WORKS
Because it does no good to have just one audible signal that a crossing light is on (the blind can't see in which direction it is safe to cross), there are two audible signals. Chirping sounds indicate that it's safe to cross streets in the east-west directions and coo-coo sounds indicate that it's safe to cross in the north-south directions. This system requires the blind to have a mental map of the streets, to know where they are and where they are going, and to have a good sense of direction.
A new device is being installed to help people who are both deaf and blind so they can safely cross intersections. This device displays a tactile signal that a person can identify when he or she touches the crosswalk button.
Legally allows a driver to park in a specific spot for a period of time in exchange for money.
Along the curbs of streets in commercial sections of towns and cities.
Excerpted from A Field Guide to Roadside Technology by Ed Sobey. Copyright © 2006 Ed Sobey. Excerpted by permission of Chicago Review Press Incorporated.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Meet the Author
Ed Sobey is the author of several hands-on science books, including Inventing Toys and Loco-Motion. He lives in Redmond, Washington.
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A Field Guide to Roadside Technology is the perfect book for the nerd. Haven't all Phoenician's wondered what those circular brass metal markers glittering like golden pucks embedded into our brownie-soft summer hell-black asphalt were? 'Geodetic Control Stations.' Or how to tell a bascule bridge from a cantilever one? Or what all those peculiar looking gizmos mounted above, below and around the poles at every intersection accomplish? Although Ed Sobey's biography is more exciting than his book, A Field Guide is packed full of need-to-know information on over one hundred arcane roadway and near-roadway artifacts. Each page features a slightly grainy black & white photo of the technology in question followed by text broke down into categories of: Behavior, Habitat, How it Works, and Interesting Facts. The author excels in explaining how things work in such a clear and concise way that even the dimwit Al Gore could understand them. (Liberal readers feel free to insert Dan Quayle in place of Al Gore.) A Field Guide to Roadside Technology, about the size of a CD wallet and sporting non-snagging rounded corners, is an excellent resource to keep on the front seat (not in the glove compartment) of the family car for those times when we are certain to be stuck in traffic.