A Spotter’s Guide to Traffic Signals

September 2, 2016 at 5:00 pm | Posted in Traffic Signals | Leave a comment
Tags: ,


Ever look at a traffic signal and wonder how old it is or who make them?  What follows is a two part “spotter’s guide” to the traffic signals of Minnesota. There is a certain slang used by people that are used by enthusiasts and collectors of traffic signals. I’ve included it here since it’s useful to describe and distinguish various models, in all cases it’s enclosed in parenthesis to make it clear that it is not official terminology. Now onto the guide:

Eaglelux KB63 “Tall Fin” and “Short Fin”

The Eagle Signal company is one of of the oldest of the signal companies, located in the Quad Cities for many years. And the oldest signals still in place in Minneapolis are the Eagleluxes, which was the original Eagle trade name for their signals. (This area has long shown a strong preference for their equipment).  Although a lot have been discarded in the recent traffic signal timing project, there still are some left, many with incandescent yellow. The most distinguishing feature of them is the art-deco like fins on the top and bottom plate. (Early sectional signals had open tops and bottom to each segment, there’s be an end plate on each end and tie rods holding the entire thing together.)

These were made from the 1930s to the mid-1950s. Early KB63s, the “Tall Fin” have a brass ID tag (normally covered by years of paint) on the bottom plate and no logo on the backs. Later there were running production changes where the fins were noticeably shortened, the Eagle logo was added to the back, and the ID plate was removed, and the fins were noticeably shortened The reason for this is speculated to be that the long fins interfered with more modern mounting hardware that was coming into use. This  configuration is known to enthusiasts as the “Short Fin”.

Spotters 01

Eaglelux “Tall Fin”, Minnehaha Ave and 46th St, Minneapolis

Spotters 02

Eaglelux “Short Fins”, Minnehaha Parkway and 50th St, Minneapolis

Spotters 03

Eaglelux backs. This is the mix of early (no logo) and late (with logo) sections and late (short fins) top and bottom plates

Eagle  “Rodded Flatback”

In the mid 1950s, Eagle dropped the Eaglelux name and introduced the “Rodded Flatback”. This was somewhat of a transition that was only in production for a few years. It introduced the simplified body style that would last for many years, but maintained the use of top and bottom plates, (now with no fins) with tie rods and the older style “slam latch” reflectors, and old small logo.  I don’t know of any that are in the field, but list it as there might be, and since it is interesting as a transition to the more modern style. Also of note this is the first that had dedicated 9” square pedestrian housings. Before if you wanted pedestrian indications you added a 4th sections to the vehicle section and installed a black and white circular “Walk” lens, or later on a separate 2-light signal with an orange “Wait” and white “Walk”.

Spotters 04

Eagle “Rodded Flatbacks” from my personal collection

Eagle KB170 / KB380 “Flatback”

In 1960 Eagle introduced this model,   Gone are the tie rods and plates, all sections now have tops and bottoms and are held in place by internal clamps, and the reflector was a modern “H” shape.  The small Eagle logo was replaced with a much larger version. The initial production had a large trapezoid above and below the eagle, enthusiasts call these these “Trapezoid Flatbacks” and only they only lasted a few years before the trapezoids were removed (the reason for them is not known).

Spotters 05

Eagle “Trapezoid Flatback, W 7th St, St. Paul. This is the only one I’ve seen in the field

Although the 8″ variety are most common, in the 1950s 12” indications were introduced and promoted by the signal companies as being more visible on the newer higher speed roads and more complicated intersections. Initially only the reds were 12”, and only on overhead mountings (which became increasingly common during that time)- 8” and 12” sections have always been able to fit together. Later all three sections were 12” (and now 8” are only allowed on lower speed roads). Eagle’s version was designated model KB380 and besides the obvious size difference looks similar to the 8”. Some KB380s are found on older installations in Minneapolis and the suburbs, but they are not overly common.

Spotters 06

Eagle “Flatback” backs

Spotters 07

Eagle “Flatback” internals. Virtually all traffic signals still have a similar design. From my personal collection

Eagle AluSig and DuraSig

In the early 1970s there was a radical redesign. With catchy trade names came a move to internal hinges, and thumbscrews instead of latches to hold the doors closed. AluSig was made of traditional aluminum, and DuraSig introduced a new material- polycarbonate. Minneapolis and St. Paul were quick to adopt polycarbonate, the other agencies and Mn/DOT were very slow to and only recently have switched. The early DuraSigs had an unfortunate design in that the reflector was attached to the door, which made it difficult to change the reflector or lens, as well as visors attached with fragile tabs instead of screw. They were later revised to a more conventional design. DuraSigs worked well up here where they were immune from salt spray, but tended to bake and become brittle in warmer climates.

Both 8” and 12” DuraSigs were wildly popular in the cities, and the 12” versions are still being installed. AluSigs were more popular with Mn/DOT and the suburbs, even then they were mainly using 12”, so 8” AluSigs are uncommon, and when found are normally a pedestrian signal or the yellow and green of a larger assembly.

Spotters 08

Eagle Alusig 8″ and 12″ combo. The 9″ worded, incandescent pedestrian signals are virtually extinct. 65th and Lyndale Ave, Richfield

AluSig backs

Spotters 09

Durasig Backs

Spotters 10

Durasig front and internals from my personal collection. The red and green are LEDs.

Later Eagle Models

In 1987 Eagle was bought by a company called Mark IV Industries. Shortly before this Mark IV had also bought out Automatic Signal. Each company had 8” and 12” vehicle and pedestrian signals in poly and aluminum, so a total of 24 products, so simplification was inevitable.The following products survived the merger:

  1. Eagle Alusig, 9″ pedestrian only as type SA, later discontinued
  2. Eagle DuraSig, 9″ and 12″ pedestrian and 8″ and 12″ vehicle as type SA
  3. Automatic polycarbonate, 8″ and 12″ vehicle as type SIG, 8
  4. Mark IV aluminum, 12″ pedestrian and 8″ and 12″ vehicle as type SIG, 8″ vehicle later discontinued.

“SIG” is known as “SG” with LEDs, and now can only be ordered that way. Of these types, SA continued to be used in the cities, while Mn/DOT and the suburbs switched to aluminum SIG exclusively, (referred to by enthusiasts as “Bubblebacks”). Mn/DOT finally switched to polycarbonate a few years ago, and suburban agencies followed, so now we’re starting to see type SA in the suburbs.

Siemens bought Mark IV’s signal products in 1997, discontinued the Eagle name, and moved Eagle away from the Quad Cities to Texas. In 2013 Siemens sold Eagle’s signal head business to a company called Brown Traffic (while keeping the more profitable control business). Brown has indicated they plan to re-introduce the Eagle name, and update the molds to the new Eagle logo, which is a realistic perched eagle rather than the stylized “Thunderbird” of the past 50 years. The headquarters has returned to the Quad Cities, although manufacturing will likely stay in Texas.

Spotters 11

Type SIG “Bubblebacks, later version, 98th and Dupont Ave / I-35W, Bloomington. Eagle visors tend to point downwards more than other brands.

Spotters 12

Early Bubbleback before the logos on the backs were removed about the time of the Siemens buyout. After this the backs were unmarked and there was “EAGLE” spelled out on in small letters on the top where it’s impossible to see from the street. From my personal collection

Econolite (and GE) Products

Econolite is based out of California.  They’re most noted by enthusiasts for producing a line of neon pedestrian signals that were ubiquitous in California (now virtually all gone), as well as distinctive looking vehicle signals. They got into the vehicle signal business in the early 1950s when General Electric, one of the early players, changed their design and sold them their old molds (In 1957 GE would exit the business entirely and sell them the remainder). I’ve seen 1950s-early 2000s Econolite products used here; there are some in St. Paul, but they tended to be used more in the suburbs.

GE, and later Econolite 8” signals were rather distinctive in that there were vertical grooves running down the back.  A late 1950s production change was to shorten the grooves so they didn’t go all the way to the end of the section due to water ingress problems. Enthusiasts refer to these as “Groove Back”, “Long Groove” and Short Groove”. The corresponding 12” signals were circular and had a concentric design, “bullet backs”, and could come with either round or square doors. (Econolite models numbers were E31 for 8″, T31 or ST31 for 12″, and C35 or SC35 for a combination, the “S” denoted square doors rather than round) These designs lasted until the early 1980s, when “Buttonback” 12” signals debuted. “Buttonbacks” lasted until the early 2000s. These were the last Econolite products I’ve seen used here.

Spotters 13

This is the only piece of GE equipment I’ve seen on the streets in Minnesota, a long defunct flasher on Vermillion Street in Hastings.

Spotters 14

Pair of GE signals in Heritage Square at the Minnesota State Fair. In the 1940s GE signals came with beautiful “Spiderweb” lenses. With Heritage Square demolished I don’t know the fate of these

Spotters 15

8″ back styles for GE, left; early Econolite, center, and later Econolite, right. From my personal collection.

Spotters 16

Econolite SC35 “Bullet back” and “Short Groove” signal, 7th St and Montreal Ave, St. Paul.

Spotters 17

Econolite “Buttonbacks”, Market Drive and Curve Crest Boulevard, Stillwater. These are very rare here, and later Econolite products (which look much like the McCain signals described below) are not used at all.

Spotters 18

Econolite “C35” (actually pieced together from different lights), along with an Econolite E8 neon pedestrian signal, this configuration was iconic of California for decades. From my personal collection.

McCain Signals

In the past decade or so McCain polycarbonate signals have been showing up. They’re very plain looking, but they do the job. 8″ models are often used  as ramp meters. Except for a smaller size they are identical.

Spotters 19

McCain 12″ vehicle signals, County 10 and County H, Mounds View

Spotters 20

McCain 12″ vehicle signals, County 10 and County H, Mounds View

Programmable Visibility Signals

In their own category are “programmable visibility” (PV) signals for when it’s desired to only allow it to be seen from a narrow viewpoint, for instance two roads the meet at a sharp angle.

3M Model 131, introduced in 1969, was the first of this design. Rather than a conventional traffic signal bulb (which resembles a standard clear incandescent), these used a compact, high intensity PAR lamps that was accessed from the back. The light from the bulb went through a frosted diffuser, and then a clear optical limiter lens, followed by the acrylic tinted Fresnel lens in the front. The whole assembly could also be tilted at different angles. How it worked is once the light was mounted, you’d go up in a bucket truck and peer through the optical limiter toward the road, seeing an inverted image of the road.  You’d then put a special 3M tape (more or less heavy duty duct tape) on the optical limiter to cover parts of the road you didn’t want to see the light.

Spotters 21

Front view of 3M traffic signals, Trunk Highway 121 and 58th St, Minneapolis

Spotters 22

3M 131 internals, front view. The top section has the wire guard and diffuser in place, the bottom section has them removed. The white object in the background of the bottom section is the lamp. Normally there would be a pole adapter on bottom, which I removed to make it sit flat on a table. Also missing is the dimmer, which would fit on the lower left. These would automatically dim the light at night, but were stripped out during LED conversions as they were not compatible.

Spotters 23

3M 131 internals rear view. Top: bulb removed, diffuser present. Bottom: Bulb present, diffuser removed. This is masked so you can see it close-up but not farther away, as might be used in two intersections really close to each other. An LED retrofit bulb is on the table.

Eventually McCain introduced their own PV signal to compete directly with 3M. They looked similar, except for the back (which is actually a re-purposed 8” section) and using standard circular visors. This area was never enthusiastic about them, preferring to support the local company. However competition and declining orders eventually led 3M to discontinue their model in 2007 so for a while McCain was the only PV option.

Spotters 24

McCain PV signals, Calhoun Pkwy and William Berry Dr, Minneapolis

As a more modern  alternative, a company called Intelight offers “electronically programmable” signals. Basically rather than a few high powered LEDs as used in most signals, there are a large number of standard LEDs in a grid. These can be selectively disabled through software to restrict the visibility, generally done by a smartphone app by a worker in the street. These have large heatsinks on the back and so are hard to mistake for anything else.

Spotters 25

Intelight fronts, Franklin Ave. and East River Parkway, Minneapolis

Spotters 26

Intelight backs.


Intellight internals

This concludes the spotters guide. I’ve left out products by a number of companies that have only a minuscule share of the equipment here, but what I have have included amounts to well over 99% of the equipment in service in Minnesota

Back to North Star Highways Home


TrackBack URI

Powered by WordPress.com.
Entries and comments feeds.