Retro Reflection

Oct. 1, 2006

Vehicles change, but the traffic headaches seem to stay the same. Congestion on the streets of ancient Rome prompted Julius Caesar to ban wheeled traffic from the city during the day in an effort to reduce congestion, according to Encyclopædia Britannica.

Vehicles change, but the traffic headaches seem to stay the same. Congestion on the streets of ancient Rome prompted Julius Caesar to ban wheeled traffic from the city during the day in an effort to reduce congestion, according to Encyclopædia Britannica.

Elementary traffic control can be as simple as deciding that vehicles should keep to the right so faster vehicles can pass on the left. Keeping to the right was one of the rules of the road laid down by Police Commissioner Bingham in New York City in 1908, according to a history of traffic on the New York City website ( The rules also specified that a driver should signal with a raised hand or whip before slowing, stopping or turning.

The first traffic control devices installed in New York in 1915 were four-armed semaphores with the words “GO” and “STOP” painted on their arms. Police traffic officers had to operate the signals manually.

A year later, the city installed a traffic signal with electric lamps colored red, amber and green. The lamps were placed on top of a tower in the middle of the intersection of Fifth Avenue and 42nd Street. The lights were manually controlled by a police officer.

The colors did not mean what the same colors mean on modern traffic signals. With the 1916 signals, drivers could get a ticket for going through a green light. In 1916, red meant traffic in all directions had to stop. An amber light meant crosstown traffic had to stop to let north-south traffic through. Green meant north- and southbound traffic had to stop so crosstown traffic could proceed.

New York was later than most American cities in adopting in 1924 the railroad signal system of red for stop, amber for slow and green for go.

William L. Potts is recognized as the inventor of the first four-way traffic signal, according to a 1947 article in Motor News. The signal was placed at the intersection of Woodward and Michigan Avenue in Detroit in October 1920. The tower was manually operated and had 12 lamps, three in each direction. Potts, who was superintendent of signals for the Detroit police department, installed his first automatic signal light system in 1921. Potts, who was aware of the railroad signal system, also is given credit by for being the first to use a yellow light in his traffic signals.

Also in 1924, the New York City Department of Plant and Structures recommended adopting the new electrically synchronized traffic signals. Although it took many years to master the art of timing the lights, a task that individual officers did before by standing in the street and directing traffic, the new traffic signals cut the time needed to cross Manhattan by about eight minutes.

In modern times, the signals at an intersection have been augmented by various devices to detect and count vehicles as they pass and adjust the timing of the signals to maximize the flow of traffic through the intersection. The next-highest-order function is to coordinate intersections to maximize traffic flow through an entire region, such as a city.

Flow control

The Golden Gate Bridge is a good exampe of a few of the contemporary methods of managing traffic to maximize flow.

Electronic toll collection, implemented in July 2000, reduced toll plaza wait times from 20 minutes to almost nothing.

The bridge is a fixed, six-lane roadway, so it cannot add lanes to accommodate heavier traffic, but it can reverse its existing lanes to add capacity in one direction at a time. This zero-sum game adds to one direction and subtracts from the other. It can be changed throughout the day to accommodate more traffic toward San Francisco during the morning commute and more traffic toward Oakland in the afternoon. Reversible lanes were implemented in October 1963.

The Golden Gate became the first major bridge in the world to offer one-way toll collection in October 1968. The strategy proved massively successful.

Bus and ferry transit systems provide other options for travelers making the Golden Gate crossing, while increasing capacity for new travelers and slowing the growth of congestion on the bridge.

A major technical development specifically in traffic signals is the growing use of light-emitting diodes (LED) instead of incandescent lightbulbs. After clearing the hurdles of extracting the right colors from the LEDs and making them bright enough to be clearly visible in daylight conditions, the devices have reached the stage where traffic managers can install them without worries and have bulbs that last longer and use less electrical power than incandescents.

In fact, the Energy Policy Act of 2005 mandates that any traffic signal modules manufactured or imported to the U.S. after Jan. 1, 2006, must meet or exceed the energy efficiency requirements of the EPA’s Energy Star program for traffic signals. In effect, the law prohibits the manufacture or importation of incandescent signals.

Another major development in traffic control was the invention of retroreflectors. These gadgets are now used in a variety of applications, such as signs, pavement markings and other devices.

Shining back

Harry Heltzer, Philip V. Palmquist and a group of colleagues developed the first fully reflective sheeting utilizing glass-bead optics in 1939. Heltzer and Palmquist were engineers at 3M at the time. They began the research in 1937 and erected the first fully reflective sign in Minnesota.

Palmquist’s later inventions included a transparent film that could be used to cover and protect the optics of the reflective sheeting.

Reflective technology has since become the industry standard.

Bill and Hugh Rowland were responsible for the invention of micro cube corner prism technology, according to the American Road & Transportation Association’s (ARTBA) list “America’s Top 100 Private Sector Transportation Design & Construction Professionals of the 20th Century.” The prisms are incorporated into reflective materials used in applications such as temporary road markers, signage, channelizing devices and high-visibility safety garments.

The Rowlands founded Reflexite Corp. in 1963. The company introduced in the early 1980s the first reflective roll-up sign, an invention that improved the visibility of highway work zones.

“In the ’20s and early ’30s, the primary means of providing retroreflectivity was somthing called ‘cat’s eyes,’ which are basically marbles,” Gene Hawkins of the Texas Transportation Institute told Roads & Bridges. The marbles were 3?8 to 9?16 in. in diam.

Later, the beads used were more the size of sand grains and then even smaller. Modern microprismatic sheeting came out in the early to mid-80s.

One of the more colorful characters in the field of traffic safety was John C. Fitch. As a race car driver, he won the Grand Prix of Argentina in 1951, the Mille Miglia (first in class, fifth overall) and the Sebring 12-hour race. Fitch raced six times in the Le Mans 24-hour race, finishing as high as third ( He designed and built racing cars from scratch. He was a fighter pilot in World War II, flying a P-51 and becoming one of the first Americans to shoot down a German ME 262 jet fighter. He was shot down himself just two months before the end of the war and became a prisoner of war. He was a sailor. He was a design consultant for racetracks.

Fitch also was—and still is at the age of 89—an inventor of safety devices for racetracks and highways. His co-driver at Le Mans in 1955, Pierre Levegh, was involved in the worst accident in racing. The crash during that race killed 85 people and led Fitch to the invention of numerous energy-absorbing safety barriers over the decades since.

The Fitch Barrier, one of his early creations, is the familiar sand-filled plastic-barrel crash cushion used all over the country in front of fixed objects, such as bridge abutments. Fitch actually crash-tested the barrier himself, according to Wikipedia. He received the Kenneth Stonex Award from the Transportation Research Board in 1998 for his contributions to the field of roadway safety.

He has invented a variety of other safety measures for racetracks and highways.

Early roadside barriers included the now-ubiquitous guardrail. In some situations, the guardrail actually poses more of a danger than the roadside conditions.

“It was intended to keep the car on the road,” Brad Sant of ARTBA told Roads & Bridges, “not necessarily to cushion the crash."

Guardrail has evolved from a structure with a blunt end, with the chance of spearing an approaching car, to having a sloped end, which prevents spearing but can launch the car into the air and into an even worse crash. Recent modifications include cable guardrail, with steel cables instead of shaped sheet metal. And guardrail posts used to be made of metal or wood fixed in place, so the vehicle hit hard. Now the posts are designed to break away on impact. The cables slow the car more gradually so there is less danger to the occupant. The posts are easily replaced and pose no threat to the vehicle.

The same kind of breakaway design is now also used for signs and light poles.

The future will surely bring even more amazing contributions to traffic management and safety. Already there is work being done on lane-departure warning systems, cruise-control units that maintain proper distance from the car ahead and collision-avoidance systems.

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