Start your engines with summer fun with TSA- 07/18/07

All TSA members, old and new, are invited to the next Traffic Signal Association – Silicon Valley Chapter’s (TSA-SVC) quarterly meeting to be held at the exciting, Malibu Grand Prix, in Redwood City at Wednesday, July 18, 2007 at 10AM.

Bring yourself, your colleagues, and loved ones and TSA-SVC will provide the food, tokens, and the racing. Regular meeting will be held on-site and immediately after the meeting will be our way of ‘networking’ and’team-building.’ We’ll just need to make sure we don’t have any knockdowns with those race cars! Email any of your TSA-SVC officers for questions……see you there July 18 at Redwood City.

Malibu Castle
320 Blomquist St.
Redwood City, CA 94063
Tel: (650) 367-1906
Malibu Grand Prix
340 Blomquist St.
Redwood City, CA 94063
Tel: (650) 366 -6463
Hours of Operation:
Monday – Sunday 10 a.m. to 11:30 p.m.

Mapquest Map

From The North
Take 101 Freeway SOUTH to the Seaport Boulevard/Woodside Road exit. Stay LEFT at the fork and take Seaport Boulevard (EAST). Make a LEFT at the first stop light onto Blomquist Street. Malibu Grand Prix is the first driveway on your LEFT, Malibu Castle is just a bit further on your LEFT.

From The South
Take 101 Freeway NORTH to the Seaport Boulevard/Woodside Road exit. Stay RIGHT at the fork and take Seaport Boulevard (EAST). Make a LEFT at the first stop light onto Blomquist Street. Malibu Grand Prix is the first driveway on your LEFT, Malibu Castle is just a bit further on your LEFT.

grand-prix2.bmp<—–Check out Dave “Andretti” Mooso

TSA Meeting Minutes for March 16, 2007

TSA-SVC, once again, had a successful quarterly meeting held at City of Cupertino’s Corporation Yard. Meeting was called to order at 10am by TSA-SVC newly elected president, Roy Dexter. Previous meeting’s minutes were reported by out-going TSA-SVC secretary, Armando Herrera. TSA-SVC newly re-elected Treasurer, Ellen Martinez, provided the Treasurer’s Report.

TSA-SVC was proud to have Mr. Mike Malcuit from Advance Traffic Products as their guest speaker who presented their product, Wavetronix Smart Sensor. Mike presented on how the Smart Sensor is “ITS industry’s ONLY auto-calibrating, auto-configuring traffic sensor.” Mike’s presentation also included a simulated, on-field calibration and operations demonstration of his product. More information on his product can be seen at Dexter then concluded the meeting with a round table discussion on any ideas for future meetings with regards to venues, discussion topics, and any other wish lists the group has. Please send all inquiries or suggestions to TSA-SVC Secretary, Robert Asuncion, at

Meeting was concluded at approximately 11:30am and all members enjoyed a catered barbeque lunch by Armadillo Willy’s of San Jose.

Next Meeting is scheduled for July 18 at 10AM at Redwood City. Malibu Grand Prix!!!!

Articles Wanted

I’ve written a pile of these articles that have appeared recently. One will appear each month on this website through at least the end of the year. They are based on my experience and opinions and do not necessarily reflect the opinion of TSA. A little pre-warning, I have been out of the business for several years. I have forgotten more that half of what I once knew and never knew half of what I should have known anyway. That may put the quality of these articles pretty low on the dipstick. If that is so, I apologize in advance. If you find any of these articles helpful, you’re welcome. If you don’t, I’m sorry to have wasted your time. If you disagree or want to share your own knowledge or experience, write an article. It doesn’t take much time. Remember, it’s the thought that counts. I can always try to polish the format and spelling if that’s all that keeps you from writing. You may even find it to be fun.

Additional Control By PLC’s

Programmable Logic Controllers (PLC) are extremely versatile control devices. They can be used very effectively in traffic control systems to provide additional functionality or connect otherwise incompatible equipment to make more effective control systems. PLC devices have been around for quite a while. Around 1988 I started looking for ways to provide additional functionality in the traffic control systems I was responsible for. The then common method was to prepare a logic box with a number of logic cards which provided various functions that implemented the desired functions. Individual cards might provide any number of functions but the most common were timers, “or” gates, and “and” gates. Anywhere from one to possibly a hundred or more might be used in conjunction with the traffic controller or other devices to implement the desired function. We had simple boxes of one or two gates that provided special flash control or controller steering for coordination purposes. We also had full railroad preemptor systems that provided complete control of all signal colors during railroad preemption. The later was a bit before the development of the microprocessor based traffic controllers we now enjoy. Needless to say, troubleshooting a problem in such a system was never a simple task. There needed to be a simpler way to do these kind of things.

I started looking at small single board computer devices. Most of these were programmed using the “C” programming language. While the device could provide the necessary control, program development to provide the desired function was not easily accomplished nor modified. There were some devices that allowed for simpler programming using “Tiny Basic”. The Basic language was much easier to work with but the command set was rather limited. Finally, I stumbled upon the Tri-PLC. This was a rather inexpensive device that was programmed using “Ladder Logic”. It also included a powerful verion of tiny basic as well, something most PLC’s do not include. The combination made a very powerful device.

Ladder Logic is a programming method that more closely matches relay and timer control systems. When running the control program, PLCs capture all inputs make the appropriate logic decisions and then set all the outputs based on the status of those inputs. This is done several times per second. This is very beneficial in that most of the problems caused by dynamic inputs to the system are eliminated without the need for exotic input and output control programming. Another great advantage was that they worked well with the 24 volt negative logic used in traffic control systems. The PLC usually had an input range of 12-33 volts using ground true inputs and open collector outputs. This was ideal.

Now PLCs had been around for a while in industrial control but the costs of the systems were quite high. The Trilogic PLC was quite economical ($200-300 or less) and came with the required programming language which included a simulator as well. A device was obtained and it did work as well as expected. I had never seen PLCs used for traffic control before, they may have been, but they are certainly more commonly used now

I was rather busy with other demands at the time so a co-worker, Tony Rucker, looked around and found a similar PLC from IDEC, more easily available locally and still reasonably priced. He then implemented several uses including Light Rail Vehicle Preemption, HOV ramp signal control and simple two phase control such as fire house exits and pedestrian crossings, among other uses.

I was very pleased to finally be rid of logic boxes and to be able to provide sophisticated control functions not otherwise available in traffic control systems.

I’ve programmed several other systems as well, implementing several systems:

  • Lead/lag pedestrian control.
  • Light Rail Vehicle Control.
  • Close Intersection Coordination.
  • Alternate return phase for RR preempt.
  • Storm Pump Flow Data Logger and Alarm.
  • Even a eight phase controller with full functionality.

Lead/lag pedestrian control.

Suppose you wanted to allow the pedestrian “walk” signal to come on before the associated green phase or allow the green to come on before the “walk”. Could your controller do this. Ours couldn’t and we needed the former. The PLC came to the rescue and made the intersection much safer. Our controller now does this, but the original function was developed using the PLC. It proved useful and was then specified for implementation in the controller.
Light Rail Vehicle Control.

Light Rail Vehicle control was implemented in two different ways. Originally, when Tony programmed the system, the PLC provided the LRV signal color outputs and basic timing because the controller had limited outputs. Later, a program was developed, though not implemented, that used the controller to provide the outputs and the PLC provided most of the timing and control, including various return phase options based on traffic demand and preempt point. In addition several preempt methods were provided such as hold, expedited service, and full preempt selectable by the traffic controller based on coordination plan.
Close Intersection Coordination.

Here’s another special need, two intersections, less than 100 feet apart. The slave intersection was not on the main street. The main street signal was six phase, later upgraded to eight. The slave intersection was five phase. Each had a full compliment of pedestrian movements. Basically the slave controller was synchronized with two progressions from the main signal and the main signal was synchronized with the feed from the slave signal.

Since the main street signal could be part of a coordinated system on the main road and had much heavier traffic, the slave intersection could serve some movements several times before the main street signal was ready to feed or receive traffic from the slave signal.

This was implemented with two traffic controllers and the PLC as the “glue.” Now the same intersections could be implemented in one 16 phase controller with only slight compromises for pedestrian control. The PLC might not be needed now, if, your controller was advanced enough to provide the necessary control.
Alternate return phase for RR preempt.

Coordination of traffic signals sometimes makes odd controls necessary. Suppose you wanted to have different return phases at the end of railroad preemptions based on coordination plan or time of day. Again, use a PLC. This was not a complex implementation using a simple six input, four output PLC to provide the functionality and, in addition, provide other flashing signal control. Two preempt channels were used and the selection steered by the PLC based on controller position.
Storm Pump Flow Data Logger And Alarm.

Not really traffic control related but suppose you needed to monitor and record flow volumes from a pump station and provide alarm and notification functions as well. Sounds like a PLC is needed here. The PLC interfaced with the existing pump control PLC and was calibrated to record the run times and flow of the four pumps at the site. Two pumps normally pumped water to the sanitary sewer for treatment and payment was based on volume discharged. In addition, when there was storm water present, the storm pumps discharged to the storm system. Run times of each pump were recorded.

The pump operation was monitored and, depending on the alarm type , notification of the appropriate personnel ( maintenance or administration) could be made.

Even An Eight Phase Controller With Full Functionality.

This was just for fun, but basically an entire traffic signal controller was programmed using a single PLC. It provided modified density control coordination, TOD, and other special functions. It was never implemented but worked well on the simulator.

Several special traffic controllers were implemented including construction lane control, pedestrian crossings, and fire station exits.

Device Tester.

The PLC is ideal for controlling and monitoring for testing devices on the bench.


If you have a special control need that your existing traffic controller does not pprovide, try using a PLC. You can easily make adjustments or changes to the control program to fine tune the system for your needs. PLCs are ideal for testing of control methods possibly before implementation by other means.

For more information about PLC ladder logic, check the Tri-PLC website.