TRAFFIC – BASICS

In 1885 in Germany, Karl Benz put his name in the history books by installing an internal combustion engine on to a small 3-wheeled machine that looked like a fat bicycle.  The new engine was a single cylinder 4-stroke, and was placed in the back of the vehicle.  It was steered by an upright tiller which did not give good control, but since the engine had less than a single horsepower of force (0.75hp), it was anything but fast.

In August of 1888, Bertha Benz took the first ever “joy ride” and then advised her husband that the transmission needed a lower gear for going up hills, which he then installed.

In the U.S. the Duryea Brothers started the first American automobile company in Massachusetts in 1893, and they were quickly followed by hundreds of others.  Small companies that used to build bicycles or horse drawn wagons were diving in to this new industry.  Most manufacturers were only producing 5 or 6 vehicles per year.  They were hand built, hand assembled, and often took about a month for a factory to construct a single vehicle.

In 1908 Henry Ford applied the assembly line methods of other industries to the construction of automobiles in Detroit.  His factory could now far out produce anyone else, and the cost of the Model T was far less than other vehicles.  Automobiles were becoming a common sight by the early 1910’s, and so were automobile crashes.

The first automobile crash in America took place just 3 years after the first American automobile was built, and there were only a handful of automobiles on the road.  In May of 1896, Henry Wells was driving a Duryea Brothers car through New York City and hit a woman on a bicycle.  The bicyclist suffered a broken leg, and Wells was thrown in jail.

There were 19th century mechanisms to control “traffic”, but they were not built for automobiles.  Railroads had been using drop down semaphores (crossing guards) for many years, and one was even constructed in London, England in 1868 to help control the movement of horse and buggies that were so common.  The illumination came from a gas lamp and was switched back and forth by an operator who stood at the base of the device.  On January 2, 1869 the London lamp exploded injuring the operator.

Automobile traffic needed something else, some type of device that could alert the driver well before they reached the intersection, and preferably something that would not blow up.  No one witnessed the carnage of automobile crashes more than police officers, so it was not surprising that it was police officers who had the biggest impact on the origin of the traffic system.

There were a variety of traffic patents beginning in the 1890s’, but the first traffic light ever actually installed anywhere was designed and constructed by Lester F. Wire, a Salt Lake police detective in 1912.  It was a hand made wooden box painted yellow, and looked somewhat like a bird house.  There were two electrically powered lights, red and green, the same stop and go colors we use today.  The light bulbs were clear glass, but the glass covers were painted.  The arrangement of traffic lights has changed since then, but the colors Wire chose became the standard around the world: red, green, and yellow (though many lights are actually more amber than yellow).

TRAFFIC LAYOUT

Even the simplest modern traffic signal system will have 3 features: the traffic signals, the traffic cabinet, and the pull boxes.  The traffic cabinet is the center point for the traffic wires.  However, many intersections will have all aerial cables.

Some intersections may have a single 4-way traffic signal strung across the intersection, however, most intersections will have 4 separate signals or signal posts.  In this case there will be 4 posts, one at each corner, and each one extending outward over the street at the crossing area, each signal post providing the lights for a single direction of traffic.  Those 4 posts are of course all fed by signal wiring, and all of it connecting in to the traffic cabinet.

Traffic cabinets are an upright structure, usually made of aluminum and about 6 feet high.  The cabinet contains the controller which operates the traffic system for that intersection.  The cabinet may be right at the intersection next to one of the posts, or in some cases it may well be away from the posts.  This often depends on how much space is available in the pedestrian area.

Every signal post has an individual pull box, and the cabinet will have a pull box as well.  The pull box is a flush mounted feature, usually about one foot across and one and a half feet long.  They are commonly made of either plastic, or a fiber/concrete compound.  It is the pull boxes where the signal wires separate, so a group of traffic wires extending to any corner of the intersection will first feed in to the pull box, one group of wires feeding the signal post at that corner, and the other wires then continuing on to the next corner.

Many intersections across the country are built in exactly this fashion.  Some may have a continual timing that never changes throughout the day, so the light will be green in both directions for the same amount of time, no matter which time of day it is.  Others will have alternating timers that can extend the amount of time on the green light at certain times of day.  If the traffic is heavier east/west during a certain time period, then the east/west light may be green longer than the other during those hours.  Holidays and diverted traffic can cause problems for an intersection like this since they will increase traffic in one direction or another, but for the most part they provide decent traffic flow on a typical street.

Traffic systems are always municipally owned, either by the city, the county, or the state.  Street lights usually operate on 120-volt current which is not at all a high voltage, but it is the same as typical household current, and more than enough to cause electrocution under the right circumstances.

Many intersections have additional features.  The most common is to have separate pedestrian posts to indicate that a pedestrian is waiting.  This will alter the pattern of the lights, but not immediately.  Many people will stand and incessantly keep pushing the button thinking that it will alter the lights faster, but that is never the case.  Pushing the button once will alter the algorithm of the timing, but no matter how many times you push it, the lights will still follow a set pattern.

Besides these pedestrian posts, there are a number of other features such as additional lights aimed at incoming traffic that may not have an adequate view.  However, these will all feed into the same traffic cabinet.  If the feature has to interact with the signals, then the signal cables will feed to the cabinet.

There are also some isolated features which do not tie in to any cabinet.  A common example is school crossing lights which are turned on by crossing guards, and are far from an intersection.  There are also some pedestrian lights designed in this same manner, but for the general public on busy streets.