Types of Traffic Signal Cabinets

Many people don't see the large boxes near the intersection that hold the signal equipment. There are several different flavors of signal control equipment. These are NEMA TS-1, NEMA TS-2 and the CalTrans TEES style control environments.

Eagle EF-20 electromechanical controller

Originally, the cabinets had electro mechanical switches and a rotary drum. They worked by having the rum rotate, and cams would engage and disengage mechanical points that would lead to circuits running the greens, yellows, and reds. Many agencies still use these types of controller assemblies. If you are standing next to a controller cabinet, and you hear it whirring, and when the lights change, you hear a clunk sound from the box, the controller may well be one of these old electro mechanical systems.

In the early 1960's, the first electronic controllers started being fielded. Everyone seemed to be doing their own thing without respect to a standard. Control equipment was produced by Singer (the same Singer as sewing machines), and at times, major companies like IBM, Raytheon and others were trying to figure out how to make better machines.

In the 1970's, two basic standards were developed. The California Department of Transportation developed a stander with a bunch of other states, and produced the Traffic Engineering Electrical Specification (TEES). About the same time, the National Electric Manufacturers Association (NEMA) produced the TS-1 specification. In the 1980's, NEMA published the TS-2 specification. Each of these specifications has matured over time, with new, updated specifications for the equipment.

In the late 1990's, several different organizations updated a standard specification for electronic communications and controller operation that is known as the National Transportation Communications Infrastructure Protocol (NTCIP). This is supposed to provide a national standard for how all of the parts and pieces within a traffic signal and ITS system.


NEMA TS-1

IDC NEMA TS1 Traffic Signal Cabinet

NEMA TS-1 is one of the older forms of control environments. Essentially, everything is communicating via a series of large wire harnesses within the cabinet. The controller has multiple milspec cannon plugs on the front and it talks with the equipment via a dedicated pinout / wire combination to the specific equipment. This is a reliable form of signal system, with some caveats. First is that the controller tells the equipment what to do, but never gets a check back from the equipment. This means that the signal controller assumes that the signal is doing what it has been told to do. There is a conflict monitor that makes sure that the signal does not malfunction.



Another issue with this type of controller is that while there are three of the cannon plugs defined by the NEMA TS-1 standard, any additional connectors are not defined. This is important, since the fourth connector plug includes how extra detection inputs are mapped, how the emergency vehicle preemption inputs are mapped, and other factors.

The basic NEMA TS-1 spec has 16 defined detection inputs. Depending on the generation of the equipment, there may only be between two and twelve phases available, and as few as 8 detection inputs. Some of the more modern NEMA TS-1 controllers can handle up to 64 detection inputs, but only 24 are really available.

The reason why this is important, is that if a cabinet is configured for one particular brand of controller, and the engineer wants to change the controller to a different brand of controller, some care needs to be given as to how the controller cabinet needs to be rewired to accommodate the new controller's inputs and outputs. This is especially true if the controller's manufacturer has a really unique hardwire mapping in the controller. For example, the Traconex CJ-32 controller is a modified NEMA TS-1 controller that has 32 unique detection inputs, however, 16 of these detection inputs are remapped to the phase hold and phase omit input pins. As long as you trade one Traconex CJ-32 for another CJ-32, it is ok, but change out the CJ-32 for a straight CJ, or and Econolite ASC/2, then you have your detection inputs causing the signal to omit and hold vehicle movements. That may not be what you are intending.

There are modern NTCIP controllers that are configured to fit in a NEMA TS-1 cabinet environment, and allow the pin inputs to be reassigned by the programming.

NEMA TS-2

Econolite TS2-1 traffic signal cabinet

NEMA TS-2 cabinets essentially refer to a controller that has a serial communications system referred to as "SDLC". This is a fancy term for a RS-485 communications system that connects the controller, Malfunction Management Unit (a fancy conflict monitor), the detection inputs, and the load bay.



There are other devices that can be added to the SDLC communications, including a frame grabber. The frame grabber is a product produced and sold by ATSI, that monitors all of the serial communications inside the system, and when an error occurs, the frame grabber will allow the engineer or technician to diagnose what was going on in a relatively simple manner.

The SDLC communications allow all of the equipment to talk back and forth, ten times per second, to send an command, and get a response that the command was executed.

Econolite Pole Mount TS2-1traffic signal cabinet

The back and forth communications allow the controller to make sure that the signal is working properly. The downside is that once in a while the SDLC communications skips a beat or two. Depending on what type of communications parameter was skipped by the communications system, this can either be logged, or actually send the signal into flash.

The Malfunction Management Unit for the NEMA TS-2 environment also monitors pedestrian WALK / Flashing DONT WALK, which the Conflict Monitor for the NEMA TS-1 environment does not.

The NEMA TS2 cabinet is usually capable of 64 unique detection inputs. The specification allows for up to 128, but I do not know of any manufacturer who has allowed for all 128 yet. 64 may sound like a lot of detection inputs, but when you start mixing and matching video, radar and loop inputs, you can eat up 64 detection inputs really fast.

Econolite NEMA TS2-1 Traffic Signal Cabinet

One of the primary considerations that the traffic engineer needs to understand with the NEMA TS2-1 is that the detection comes in groups of 16 on a Bus Interface Unit (BIU). This means that if you are going to need 17 detection inputs for a TS2 video detection system, you need to reserve all 32 detection inputs on 2 BIU's, which reduces the number of loop channels available. Alternately, the engineer could use a TS1 video detection card, and then each camera would have 4 unique detection inputs.

In the picture above, the controller is a 2070 controller, configured to operate in a NEMA TS2-1 environment.

One of the primary advantages of the NEMA TS-2 cabinet is that the internal communications are pretty standard. This allows for a very easy swap out of one brand / make / model of a controller for another. There should be very limited wiring differences between manufacturers. One of the few that may need to be addressed is if the signal is operating with FSK communications, the connector for the inter-cabinet communication may need to be modified. Where with the TS-1 cabinet, there are approximately 65 wires that have to be modified on the D connector, and if the controller uses another connector, maybe another 35 or so on the fifth connector.

Since the TS-2 cabinet talks via the serial RS-485 communications bus, it is very easy to swap out equipment.

One of my criticisms of the NEMA TS2 standard is that it was intended to provide a lower cost cabinet than a TS1 cabinet.  This was because the TS2 standard was supposed to have a lot less work in the manufacturing process.  Instead of having technicians wiring harnesses with 50 to 70 wires in each of 4 or 5 bundles, there would be a simple serial connection connecting the equipment.  The reality is, the TS2 spec has a relatively expensive component to talk between the equipment, the BIU.  Any savings in less cost due to simplicity of manufacture is added back in when you have to purchase 4 to 8 BIU cards, at $250 to $300 each, depending on manufacturer.  

Safetran TS2 Rackmount Cabinet

Safetran has a modified TS2 cabinet that is on a 19-in rack, designed to fit into a standard 332 shell.  The picture on the side shows a double wide version we had custom built for us.

The custom version included a double wide cabinet, including racks for 64 detection channels.  IT also modified the Econolite cabinet standard to replace the special MMU and TS2 5 Amp power supply with cables on the front, so we could use a normal MMU and power supply.

This custom TS2 rackmount cabinet also included switches for pedestrian calls, stop time etc.

The cabinet picture shows the signal in shop testing.  This picture was documenting that we could take the 2070 controller running Naztec Apogee software and quickly install an Econolite ASC/2 by simply hooking up the power, switching the SDLC cable to the ASC/2, and making minor programming modifications in the ASC/2 to run the signal.

This showed us that the TS2-1 operation was truly flexible, allowing us to easily change the controller without worrying about all of the special wiring in a TS1 cabinet.

Hybrid NEMA TS2-2

There is a hybrid NEMA TS2 cabinet where the load bay runs off cannon plugs and the detection inputs run off the SDLC communications. This can be handy if you have an older cabinet, and just want to add a video detection system without messing around with the cabinet wiring.

Some agencies also use this type of configuration because they want hardwired outputs from the controller but want the flexibility of the SDLC detection.

We are building a couple of these, taking TS1 cabinets out of service and modifying them.  This summer, we will have 4 in the field. Pictures, comments and other banter to come!

332 (CalTrans TEES)

The CalTrans TEES cabinet is a family of cabinets that are sometimes erroneously referred to as "332" cabinets. A 332 cabinet is one of the CalTrans style of cabinets. There are a bunch of different types of cabinets, within the family.

Safetran 332 (modified) traffic signal cabinet

In general, most 332 style cabinets are specifically wired to allow 26 detection inputs, with up to 46 detention inputs. This is done via a standard wiring harness and bridging of the detection inputs so that the there is a very standard pattern of where the detection comes in, and what the controller sees.

This type of standard wiring can be modified, and has in some cases, to allow each detection channel on the input files to have a unique detection channel on the controller. This can allow 46 unique vehicle detection channels, 4 emergency vehicle preemption channels, 4 pedestrian isolator switches and 2 channels of railroad preemption just by reassigning the wires on the existing C1 plug, assigning new inputs to the C11 plug, removing the bridging of the detection channels, and using a 2070 controller with an NTCIP style controller..

The advantage to the 332 style cabinet is that they are simple, robust, and cheap. They are essentially clones. The engineer is held by the rigid control of the 19 inch rack mount structure, and the limited choices that system holds. If anyone wants to argue, please try putting a fiber distribution unit, a couple of fiber switches, a video detection system, a video encoder and some DIN rail mounted radar units into a standard single wide cabinet. It gets really tight.

Double Wide 332 (modified) cabinet

The CalTrans Tees type of cabinets can be configures as a double wide cabinet, which does provide a very nice solution for having the traffic signal equipment on one side, and the Intelligent Transportation Systems gear on the other.

Blah, blah, blah. What does that mean? Essentially, the 332 style of cabinet can be a very powerful device.

There are some unique aspects to running a 332 cabinet that the engineer and tech need to know about.

The cabinet will run normally with the monitor removed and the door open. The NEMA TS-1 and NEMA TS-2 cabinets should drop to all-red flash if the monitor is removed. This can be a problem on the 332 style cabinets, if you remove the monitor, and don't secure the door open. If the door is unsecured with the monitor out, and opens and shuts, the drivers will see the signal go from normal operation to all-red flash, back to normal operation and flash every time the door closes and opens.

Putting the cabinet into all-red flash does not apply stop time to the controller. This means that if the cabinet is put into flash, then out of flash, the controller has continued to cycle away. If the cabinet is put into all-red flash, then taken out a few seconds later, the signal may have very different indications lit than what was operating when it went into flash.

Many 332 style cabinets to not have a hardwired stop time switch. Some controllers have the ability to assign the AUX switch on the front of the controller as a stop time switch.

The cabinet may be wired with a detection display panel. Many agencies have the display panel configured such that there are a bunch of detection switches, and if the switch is broken, or is not flipped to the correct position, the detection amplifier will place calls, but the switch will prevent the call from going into the controller.

If you have the cabinet set to normal operation (not switched into all-red flash), and you turn off the controller power, or remove the controller, all of the signal indications will go dark. To remedy this, manually set the cabinet into into FLASH and it should begin all-red flash.

Hybrid 332 (Part CalTrans TEES - Part TS2)

One of the interesting possibilities is that some traffic signal controllers are capable of being set up in a 332 cabinet (C1 FIO), while simultaneously running TS2 detection.  The Naztec 2070 controller running Apogee is one that can do this.  The NW Signal Voyage software had a software release in February 2012 that also allowed this.  I have heard that the Econolite ASC/3 and Siemens software can do this also, but have not seen this.

If this seems wacky, consider this.  If you have a 332 cabinet, with a normal wiring, you have 26 detection inputs.  This hybrid application allows you to either connect to the serial connection on the 2070-2B card, or install a 2070-7B card (depending on the software), and add new detection.  For instance, you can keep all of your I and J input files, and add 32 channels of video detection.  This requires that you have a video detection system that allows for BIU emulation (Econolite, Peek and Iteris have this, there may be others).

In other words, if you have a signal that is going to have major construction going on, and after the construction is over, the loops are going right back where they were, you can add the cameras to the mastarms, wire them in to the video detection system, and connect the SDLC communications to the controller, turn on the BIU's 3 and 4, turn off the loop detection channels, and whammo, you have new detection without turning your controller upside down.

We have ordered the parts from Safetran to replace the I and J files with the 19-in rackmount TS2 detection racks.  We will be experimenting with having a 332 cabinet running solely with TS2 detection.  More to follow on that in another post. 

ATC

Another standard of traffic signal cabinet is the new ATC standard.  This is serialized cabinet that looks similar to the CalTrans TEES (332) style cabinet, but instead of a large bundle of parallel wires connecting equipment, there is a serial interface, similar to the TS2 operation, but on a completely different standard.  These have a bit of a bad reputation in some circles, because the first ones sold were exceptionally expensive.  They provide some nice features, such as being able to support many more load switches than a NEMA or 332 cabinet.

There are some things I like about this cabinet, including the ability to have more load switches than other cabinets, and for the record, I have designed signals where I wanted 20 load switches, instead of the 18 I could use on a fully loaded 332.

The things I don't like about this cabinet is the monitor is a multi-module device, where instead of having a physical board (either diode card for a 332, or a permissive card for the NEMA cabinets), there is a hardware key that is programmed.  It most likely works just fine, I just can't make the jump from a physical contact I can measure and verify to a software / hardware only.

Another thing that concerns me is that the only pluggables I have seen for the cabinet (SIU's, monitors etc) are made by EDI.  I have no problems with EDI equipment, they make very good equipment, and I have a lot of it in the street.  This is not a comment about their products, however I am concerned about going to any device that has only one manufacturer.  For the NEMA and 332 cabinet environments, there are multiple manufacturers of all of the pluggables, so I don't worry about any of the companies going out of business, the competition driving pricing, or the decision by one company to no longer produce a product.  When there is one company, even a very good company, it makes me nervous.

Another concern with this design is that there isn't a lot of room in that big cabinet for other things, FDU's, Ethernet switches, etc.