, Michigan. In the museum hangs the
first 4 way signal ever made using red, yellow and green lights. The signal was
made by William Potts of the Detroit Police Department, and was made of a
wood frame with a sheet metal covering. It has 3 light bulbs, similar to the old
3 bulb Darley 4 ways, so on two of the four sides, the red and green lenses had
to be reversed from the positions we are used to today. The lenses were 4 inch
diameter railroad lenses. It was first installed at the intersection of Woodward
Ave. and Fort Street in October, 1920. It remained in service for four years.
Here is a video of the original Potts signal on
display in The Henry Ford Museum. Note, the sequence is not correct for this
signal. It looks like a typical signal from the front, but on the side, it goes
from green to red with no yellow clearance.
After seeing this signal on display, I wanted
to add one to The Traffic Signal Museum. Since there is no chance of obtaining
an original, I decided that I could make a replica to look like the original.
Below are photos of my version of the Potts 4 way. The goal was not to make the
signal the same way Potts made his, but just to make one that looked like a
Below is a picture of all of the parts
involved. The first parts I obtained for this signal were the lenses. I could
not make the lenses so I had to get them first and then make the rest of the
signal to fit them. From information obtained on the web, and from seeing the
signal in person, I learned that the lenses were 4 inches in diameter. I found 4
complete sets of these, made by Kopp Glass, from a seller on ebay.
The parts that make up the body of the signal
are 3/16" x 8" steel plates. Before I started the project, I emailed
Henry Ford Museum and asked for the dimensions of the original. I waited for a
reply for quite some time, but after a while I figured I would not get an
answer. Based on pictures and the knowledge that the lenses were 4 inches in
diameter, I made a guess as to the rest of the dimensions of the signal. I made
my signal 8 3/16" wide and 28 1/4 inches long with 9 inches from center of
lens to center of lens. After I finished making the body panels of the signal, I
got an answer from Henry Ford about the size of the original Potts signal. It is
9" wide and 29" long with 9 1/2" from center of lens to center of
lens. I was floored that I made all of my guess's to within an inch of the
Below is a picture of one of the body panels
next to a standard 8 inch signal to give an idea of the size. Also pictured are
the visors. This was the trickiest part to make. I found aluminum chimney
flashing and cut the visors out of that, then riveted the ends together to hold
the round shape.
Here are some more pictures of this project as
I assembled it for the first time, unpainted.
Finally, below are some pictures of this signal
after it was painted. The original signal in the museum looked black to me, so I
painted mine black, but the one picture above of the original looks like it
could be dark green.
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