A history of traffic lights

Why traffic lights? Quite simply … it’s what I do for a living!  I design traffic signal junctions and signalised crossings.

I can hear you asking “Well, that’s all lovely, Kev, but why put it on your blog?”.

Short answer is that I needed a subject for a new post and, in the end, I decided to go start a series of posts on my job.  Nothing job-specific like what I’m actually working on at the moment … I doubt my bosses would be too pleased!

No, I figured it would be safer to be more general and discuss some of the elements of the job, without getting too technical, in the hopes that some of you would (a) find it interesting and (b) learn some things about the subject.

In future posts I’ll explain the subtle differences of the various types of crossing that you’ve probably spotted on your regular journey around your town, as well as the methods that local authorities have at their disposal to control the signalised junctions in their areas and how they work.

So, what better place to start than … well … the beginning!

The story begins in 1868 in London.  It’s December and a mysterious contraption is erected at the junction of George Street and Bridge Street, close to the Houses of Parliament.

At that time it was not uncommon to experience traffic jams in the bustling city streets, not with motor vehicles, but with horse-drawn carts and drays, hansom cabs, omnibuses, and pedestrians all clogging the city streets. A journey through London was also complicated by the many road-works for a new sewer system and the over ground and underground railways.

The first signals

Early signalThat contraption turned out to be the world’s first attempt to control traffic on the roads and it’s main purpose was to provide a means for pedestrians to affect a safe crossing of the roads.  Obviously, being so close to Parliament, it is highly probable that they were there for the Members of Parliament more than anyone else!

The signal was a “semaphore” based system, rather than the three coloured lamps that we know today.

The semaphore was a tall post with moveable arms, operated by a Police officer. When the arms stuck straight out sideways, it meant stop. At night a gas light at the top was lit. The light had a red lens for stop and a green lens for go.

On January 2, 1869, a gas leak resulted in the lamp exploding, causing serious injury to the policeman who was operating it.

The American connection

TrafficSignalInstallationUS1940The man responsible for the design of that early system was a railway engineer by the name of John Peake Knight, who at the time was designing signalling systems for the railways and simply transferred the idea to the road.

Unfortunately, after the accident meant that his system was never used again and London had to wait until 1929 before traffic signals made a reappearance.

The traffic light as we know it was an American invention.  Exactly who invented it is a matter of contention.

In 1912, a Salt Lake City, Utah, police officer named Lester Wire mounted a handmade wooden box with coloured red and green lights on a pole, with the wires attached to an overhead trolley.

But the most favoured inventor is one Garrett Morgan.  He is given credit for having invented the traffic signal based on his T-shaped design, patented in 1923 and later reportedly sold to General Electric.

It is widely regarded that the world’s first electric traffic signal was installed on the corner of Euclid Avenue and East 105th Street in Cleveland, Ohio, in August 1914.  That system was based on a design by James Hoge, who received U.S. patent 1,251,666 for his “Municipal Traffic Control System” in 1918.  It consisted of four pairs of red and green lights that served as stop-go indicators, each mounted on a corner post.

Coloured Lights

LED_Traffic_LightThe red-amber-green colour system derives from a system used by the US rail industry from the 1830s.

The rail companies wanted a means to let their engineers know when to stop or go, with different colours representing different actions.  RED was chosen as STOP because red had long been considered to indicate danger. The other colours were originally white for GO and green for CAUTION.

However, the use of a white light caused some problems. In 1914 it was reported that a red lens fell out of its holder leaving the white light exposed. This resulted in a train  inadvertently running a “STOP” signal and crashing into another train. After this it was decided to change to the now common, green for GO and yellow for caution.

Modern signals still use the red, yellow, and green colours, which were standardised in the US in 1935 as means to ensuring that all traffic signals looked the same throughout the country.