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Bicycle Discriminating Detectors Are Here

At the last TSA meeting on Wednesday. Mike Beck presented information on the MS SEDOC Intersector a new microwave based vehicle detector available from Western Pacific Signal.  It provides motion and presence detection and provides a bicycle discrimination capability.  The bicycle discriminattion detection is the most interesting feature. Now it is possible to provide traffic responsive bicycle appropriate traffic signal timing (green extension and clearance)  for controllers that provide that capability like the Naztec NTCIP Based TS2 / 2070 Controllers.

The unit demonstrated provides eight zones of detection and four outputs so it is capable of detection for four lanes. To provide vehicle and bicycle detection for each of four lanes two zones would be needed for each lane but with the limit of four outputs, some lanes would have to be combined. In the future, modules with more zones and outputs will be available. Currently up to five units may be installed at the same intersection.

This feature is even more interesting with new legislation in California, AB1581, that requires new or modified traffic signal detectors to have bicycle detection capability.

Microwave detection, with these new features, may eliminate many of the problems associated with other technologies like video (weather and lighting) and loops (roadway cuts and damage by roadwork).

It looks like this technology may be capable of much more in the future. Queue detection would be nice for modified density features that can properly respond for right turn lanes and protected /permissive left turn lanes. More outputs, more zones, and the ability to link the units settings database to traffic management systems.

I’m looking forward to some long needed improvements to traffic control using detectors that provide bicycle discriminating features like this..

Clearance Times

There is an interesting article that appeared in the January 2008 ITE Journal written by Steven M. Click Ph.D., P.E. Application of the ITE Change and Clearance Interval Formulas in North Carolina. It provides a good analysis of clearance time interval determination. You need to log into the ITE site to read the article or find a copy of the journal.

Among other things, it shows the importance of timing intervals specific to the particular intersection not a one size fits all determination, especially for the red clearance or all red interval. Unfortunately, it doesn’t address bicycle timing, which can be a concern, if your controller provides the capability of separate bicycle clearance intervals like the Naztec controller can.For easier field review, I would suggest the preparation of a table with intersection clearance distance on the X-axis and approach speeds on the y-axis. Then provide the calculated vehicle yellow clearance, vehicle red clearance, and bicycle red clearance intervals for each combination of speed and distance. The table should show the actual controller settings, not the clearance intervals so red clearance is actually your minimum red clearance setting unless yellow clearance subtracted from the calculated red clearance is greater than your minimum red clearance. It is easily prepared using a spreadsheet. The formulas could be tailored to your agencies specific methods. The table would allow quick review in the field, without the need to run through the calculations each time. The more detailed timing determination can be performed at the design stage but so many things can slip by, like a new crosswalk, a new lane, or some other change that could affect timing. The “tool” would allow the check to be part of a regular review process.

My History With Traffic Controllers

I started in this business near the end of the electro mechanical era of traffic control, at least for where I worked. During my career, systems have advanced through transistors, integrated circuits, microprocessors and into the advanced traffic control era. Below is a list of some of the systems.

Mechanical.

Fixed timer: This consisted of a switching cam which was advanced by one to three interval timers. When I started in this business, we had one of these in each cabinet as an emergency replacement controller.

Electro-mechanical: These come in many forms. We used various models.

Automatic Signal #1826: A three phase controller that provided gap timing in addition to basic minimum maximum, and yellow timing.

Automatic Signal #1022: A two phase controller that provided added initial and three types of gap reduction in addition to basic timing.

Automatic Signal #1033: A three phase controller that provided added initial and gap reduction in addition to basic timing.

All of these utilized a switching cam to control the outputs. The cam was advanced based on timing intervals controlled by adjusting a potentiometer (knob) that varied the rate of charge of a capacitor. When the voltage on the capacitor reached the set voltage, the capacitor would be discharged and the cam would advance.

To make up a useful system, other equipment needed to be utilized.

Automatic Signal #MM3 (Minor Movement 3): This was a split phase device that received inputs from a phase (parent) of the above controllers (1826, 1022, or 1033) and provided some additional timing for an additional phase and control of the outputs of that additional phase and the parent phase.

Automatic Signal #PT2 (Pedestrian Timer 2): This device had a timer driven adjustable cam that provided “walk” and “don’t walk” outputs.

Automatic Signal #TM27 and TM30: These devices were similar to a fixed timer but had three interval timers with offset synchronization adjustment capability. They were used to coordinate adjacent intersection controllers in a coordinated system.

Automatic Signal #TM1: This device was used to determine the traffic volume on the roadway and select a cycle length and offset command for the system. Basically, the settings were used to set the charge rate of a capacitor that was charged by each actuation if the input. There were two channels one for each direction on the main road. The charge levels at the end of a sample period determined how the outputs for cycle length and offset were set. These commands were then sent to the TM27 (or TM30) at each intersection.

Each of the above pieces of equipment needed to be completely disassembled, cleaned, inspected and reassembled, then adjusted every six months. In addition to the controllers, there were numerous relays used in the cabinet to provide various control functions and to drive the field indications. They also need to be cleaned, inspected and adjusted as well. A standard van could carry enough to replace the equipment at two locations. It took about four hours for two people to change out the equipment and check operation at the two locations. Solid state and microprocessor controllers eliminated all that work.

Transistor based.

Automatic Signal MF80 (or #T1055): This was a transistor based traffic controller. It provided up to eight phases in one box but basically worked the same as the earlier controllers, just that it was solid state and didn’t utilize relays. This controller provided added initial and gap reduction along with pedestrian and max two capabilities for each phase. For our systems, the TM1 and TM30’s were still used to coordinate the controllers. It was a modular controller allowing configurations based on the number of phases to be controlled up to eight.

Integrated circuit based.

Econolite D8000: This controller utilized the first integrated circuits (Diode Transistor Logic DTL). It was quite sophisticated. But basically mimicked the operation of the MF80 controller. It did utilize digital timing rather than the analog timing used on the MF80. The timing was set using decimal dial switches. It was a modular controller allowing configurations based on the number of phases to be controlled up to eight.

Econolite D7000: This was a local coordinator used with the D8000 system. The D7000 was much more sophisticated than the older coordination system. In addition to standard cycle and offset control, it provided two pedestrian permissive periods and split adjustment based on queue length on the side street.

Econolite D9000: This master controller used either volume or occupancy to determine a cycle and offset. Our system had one of each along with a programming matrix to determine the cycle and offset for the system based on both volume and occupancy. This was one of the most sophisticated coordination systems I’ve ever seen, and not a microprocessor in sight.

Automatic Signal Series 90: This controller was unique in that it utilized wire wrapped circuitry using TTL logic and was programmed utilizing punched paper cards for each phase. It was not microprocessor based. It basically replaced the MF80 controller in an Automatic Signal system.

Microprocessor based.

Econolite EMC8000: The first single board microprocessor based controller. This uses dip switches like the SPC8000 with the interval settings in binary as well.

Econolite EMC7000: A local controller of similar design to the EMC8000 controller with most of the functionality of the older D7000. Basically the queue functions were missing. Replaced with more control of the cycles and offsets.

Econolite EMC10000: This master controller provided most of the functionality of the dual D9000 masters with the program matrix. A rather effective master controller.

Econolite SPC8000: I believe this was our first microprocessor based controller.The timing intervals were set using binary numbers with dip switches on the front panel of the modules. It was a modular controller allowing configurations based on the number of phases to be controlled up to eight. This controller included a special coordination module specific for our use called the Platoon Progression module. It basically provided a non cycle based coordination method that effectively could do mini preemptions to the main street to allow the passage of identified platoons approaching the intersection. Some people traveling the road said it worked well. Others didn’t think so? This was also a closed loop system in that all controllers could communicate to a centrally located master near the center of the 18 intersection in the system . There was some remote monitoring capabilities.

KMC8000: A microprocessor Based controller that was keyboard or system programmed using a keyboard or through system communications. Real timeclock and coordination functions were included in the controller.

KMC10000: A master controller constructed much like the KMC8000 controller used as the master to several KMC8000’s in a coordinated system.

Multisonics 720?: This controller was microprocessor based and utilized program pins to make timing adjustments. It was a modular controller allowing configurations based on the number of phases to be controlled up to eight. We had two of these controller. They were used in stand alone locations.

Traconex 290: These were microprocessor based controllers. A unique feature was the case which was similar to an apple computers construction, not the usual sheet metal construction. There was a numeric keypad for programming in addition to downloading programming. It provided normal eight phase control with real time and system control.

Traconex 390: This master controller provided a full closed loop system, our first. The computer used as the central computer was the KayPro computer, later utilizing IBM PC’s.

Eagle Marc 300?: Another microprocessor based controller much like the Traconex. It provided some powerful coordination capabilities not present in the Traconex 390. We were able to utilize this system to allow non stop runs through our eight mile 18 intersection system. Utilizing lead/lag left turns and metered entrance to the system. Quite an effective system.

Naztec 900: This Advanced Controller provides all the standard functions of a secondary controller (controller and local coordinator). The same controller is used as the Primary or master controller as well with only a downloaded program difference. At the master location, there was only one box doing all functions local controller and coordinator and master controller. This controller provided many advanced coordination capabilities. In addition, there was a burnout lamp detection system utilizing the controller that could identify a single burned out lamp including identification of phase and color. It might have been very useful except for the advent of LED signal displays which made burnout detection totally obsolete. In 1988 I wrote a very detailed specification for this controller. My intent was the ultimate controller. Naztec did an outstanding job of providing all of the specified features by developing the 900 series controller. It is still possibly one of the most advanced controllers available.

Summary:
There have been quite a few changes over the years. There are many other types, makes and models of traffic control devices. These are the main ones I have worked with over the years. Probably 80% of our intersections were part of coordinated systems. Most locations were 5-8 phases. This was true no matter which of the above systems were utilized. The last of the electro-mechanical controllers disappeared in the late 70’s. The last of the non microprocessor based controllers in the early 80’s. Our entire controller base was upgraded to the Naztec controllers in 1989-1990. Naztec controllers are still utilized though there have been a few upgrades and replacements.

This is how I remember it. It may or may not all be true but I’m sticking to the story until proved otherwise.

Grounding and Bonding

Maintaining good bonding on traffic signal installations is an important part of the maintenance of these systems. Most traffic signal standards, controller cabinets, and etc are metallic and therefore are good conductors. When these systems are properly installed, they are bonded together and grounded to provide protection from shorts of the wiring to the conduits, standards and cabinets. If there is a wiring fault, the circuit breaker will then trip.

If the bonding is not installed, is broken, or has a high resistance then, not only might the circuit breaker not trip if there is a short but the conduit, standard or cabinet my become hot and present a shock hazard.Visual inspection may not be enough. A high resistance connection may occur while the mechanical connection still exists. This is especially true in older installations. A Ground Resistance Tester should be used to identify problems. Of course, you could also just measure for voltage across connections and between conduits and standards or to the neutral conductor.

I remember two occasions in particular where this problem exhibited itself.

A bicyclist called and said he felt a tingle when he pushed the bike push button. When I checked the location, I didn’t feel the tingle, but again, that doesn’t mean there isn’t a problem. I measured 35 volts AC from the standard to the conduit. My electrician shoes do work!

Since I measured the voltage, it means there were at least two problems with the installation. Of course, the bonding had a problem. But, also rather important was why was there voltage present at all. Was it just inductive or was there a wiring fault. Of course there was a fault. Induced voltage in typical systems with typical wiring distances is usually below 5 volts. I inspected each traffic signal head and found a pinched wire from one of the lamp sockets to the reflector frame. I corrected the fault then corrected the conduit bonding. Then checked the voltage on the standard and all was well. I then checked all the other standards.

On another occasion, I was troubleshooting a traffic signal wiring problem looking for why a conflict monitor was randomly tripping. The induced voltages at the cabinet field terminals were higher than normal. When I measured in one pull-box I found more than a 12 volt differential between some conduits. When the bonding was corrected, even though the bonding wires were in place, the conflict monitor tripping problem disappeared.

You might think that a standard with its reinforcing steel and anchor bolts would provide a good ground, likewise for a metal conduit. It might, but even if it did, there can be a considerable voltage drop across the ground path through the earth. That’s why the bonding is important.

Now that most newer installations utilize non-metallic conduit, bonding is still at least as important.

I don’t want to ramble on too much about this, just bring the thought to your attention for consideration.

Vehicle Detection, What’s Best?

There are many types of vehicle detectors and sensors available. Which one is the best. It depends.

Inductive Loop Detector: Loop detectors, with regular preventative maintenance of checking loop operation and condition, provide good service. In addition, the loop detector can be designed to detect field wire problems and go into a fail-safe condition. Loop detectors can detect vehicles of all sizes and shapes, classify vehicles, determine speed, and discriminate vehicles. Detection zone is made specific due to physical location but there can be adjacent lane detection, especially with improperly installed loops. They do require some form and quantity of metal to allow detection. They can provide vehicle discrimination, vehicle counting, and special vehicle detection.
Video Detectors: There are several types of video detection. Many claim to be able to detect vehicles under all conditions. That is probably an exaggeration. Video detection systems can be weak, in my opinion. There is a chance of not detecting a vehicle, especially during twilight periods or bad weather. Since there is no exact way of knowing when a vehicle is left un-detected some other means of guarantying service is needed. In order to assure service of all approaches in a “fail-safe” manner, all phases using video detection would need to be left on vehicle recall. When video detection systems are used, their operation needs to be regularly checked. If there are any video alignment changes, they should be corrected. Since they are optical, lens and enclosures should be regularly cleaned. Video detection has problems with occlusion of the detection zone and detection of shadows.
Microwave Detectors: There are simple and complex microwave detectors. Simple detectors are point and shoot. Aim them at the vehicle approach and they provide a contact closure when a vehicle passes through the detection zone. Most only detect moving vehicles and can’t provide a presence detection output.More sophisticated microwave detectors like the Wavetek can do much more. They can provide complex conditions for the turning on the outputs to the controller. Vehicle speed range and detection zone can be used. They seem ideal for detection of vehicle queues and platoons. They are limited in that there is no way to isolate lanes so left and right turning vehicles are included along with through traffic. Manufacturers claim that weather does not affect the operation.

So, What’s Best?

It really depends on the intended use. Traffic signals should be “fail-safe.” That’s where video and microwave detection systems are weak, in my opinion. If only one type of detection is used at an intersection, I believe it should be inductive loop.

This does not mean that video and microwave detection don’t have their uses. They can be effectively used for traffic sampling, vehicle counting, queue detection, vehicle tracking and more. The cost of installation may be lower for large installations. If lane changes may occur, they are easier to reconfigure to the new lanes. Damage due to construction activity will be much less since nothing is buried. The problem is that detection accuracy is lower than inductive loop detection and detection can’t be made “fail-safe.”

I know, I’m old fashioned. New technolegy is always more capable. Right. Not always. I find the old ways are often still the best or at least as good. I do like technology and think that when it is applied properly, does help with traffic management. I just wouldn’t throw away the old technology just yet. The right approach is likely a combination of vehicle detection methods.

Why Use Countdown Pedestrian Displays

Countdown pedestrian displays are LED pedestrian displays that include a two digit numeric display, along with an overlaid hand/man display. The numeric display counts down either from the beginning of pedestrian walk interval (man) through the pedestrian clearance (hand) interval or just during the pedestrian clearance interval (hand). The countdown display period is based on the last interval display periods. They are intended to eliminate the nagging complaint about the pedestrian signal not providing enough time to cross the street. They provide feedback to the pedestrian that there is a known amount of time remaining to cross the street. I disagree with the use of countdown pedestrian displays. They actually reduce safety in my opinion. Here is why I think so.

  • The time period is based on the last display period. So you must now be very careful that the pedestrian intervals remain the same or there may be a hazard when going to a shorter interval. This might happen if your controller has Max II capabilities that include the pedestrian intervals. It also might happen due to train or other preemption. The pedestrian will think they still have plenty of time and then the display will disappear. Not good.
  • The overlaid display for the hand/man display presents a potential failure problem if there is a short in the display LEDs. I’ve seen it happen. This will most likely not be reflected back to the field wires and thereby will not be detected by the conflict monitor.
  • I’ve also seen the display decide to countdown when the pedestrian display is steady orange and there is an opposing green vehicle display. Again not good. There is no way to failsafe the device to assure that if the countdown display is counting down, when there is an conflicting signal, that the conflict monitor would place the system in flash. I’ve seen this happen on three occasions.
  • The display likely has a single control board. This means it can not be made failsafe because failures can occur that are not reflected to the field wiring so the conflict monitor will not see the failure.
  • Contrary to the desire to make the crossing safer, I believe that showing the period remaining encourages pedestrians (especially children) to start across when they would not have if only the flashing hand were displayed. I believe that the best safety is provided by using appropriate pedestrian intervals and installing appropriate pedestrian information signs that explain how the signal functions and that you shouldn’t start across except when the “walking man” is displayed.

I believe that the pedestrian display should be capable of being monitored. That the design should provide totally separate display, control and power supplies for both the pedestrian walk and pedestrian clearance displays and that the countdown display should not be used. In addition, regular checks of the operation and pedestrian intervals should be made.

These are just my thought, what do you think?

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.

Summary.

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.

Real Fail Safe

One of the most important considerations when designing traffic signals is that they be “fail safe”. If something fails, it should go to a safe condition. Of course, that operation should be maintained throughout the life of the installation.

In the old days, this form of operation was often a simple interlocking operation of the relays used to control the signals. If the main street was green, the side street was forced to red. With the advent of the use of microprocessors and other solid state electronics in traffic signal systems and as the systems become more complex with more than just the two directions being controlled, sometimes the old idea of fail safe operation gets lost. New intersections often control eight or more movements with all sorts of adaptive timing. Still, it’s vitally important that the system fail in a safe condition.

Nothing can be assumed, especially that the manufacturer has designed and tested everything to that standard. There should be a full test of all new devices to assure they work as expected.

Here are a couple of the types of design errors that need to be checked for:

When microprocessors began to be used in signal monitors, it was assumed that everything was working well with simple tests of the monitor that applied a voltage to conflicting inputs and the monitor tripped. As it turns out, this test failed on at least two counts. The test facility uses a different form of power than is used in the street and that a street light circuit might short and cause the conflicting input.

The later happened during an installation. Street lights are usually 240 volt while the traffic signals are on a 120 volt circuit. In actuality, the power at the signal is just like the residential power at your home. It’s a split 240/120 circuit which is actually a two phase circuit with the peak voltage on each phase 180 degrees out of phase. The manufacturer programmed the conflict monitor to only look at the one phase of the power, the one the monitor was powered by. The problem was that one lead of the street light circuit was on the opposite phase that was not monitored. That power could, and did turn on a green light without the monitor detecting it.

This failure was noticed by a very alert inspector and reported. In the shop, the system was tested and worked perfectly, even when an out of phase voltage was applied. This pointed out the other failure. In the shop, the building is powered by three phase power; each leg is 120 degrees out of phase. This difference allowed the system to work. Evidently, the manufacturer had similar power in his plant.

As it happened, we had two systems under test in our shop from different manufacturers. Both systems had the same problem. One manufacturer reprogrammed his monitor and then the system worked properly. The other manufacturer didn’t see it as a problem but replaced the monitors in his systems with older analog devices which then made his system acceptable to us. Unfortunately, that manufacturer continued to sell the monitors that we rejected for years thereafter. We never accepted any other equipment from that manufacturer.

Another place where microprocessors seem to have reduced the old fail safe ideal is that old controllers had circuitry within themselves that prevented conflicting signal conditions. Back in the really old days, it was in the real circuit design, later in the old transistor and integrated circuit days there was similar circuitry. With the microprocessor controllers, the “circuitry” is in the firmware or programming. How many customers look at the code to see if the manufacturer really made any such consideration? And if they did, are they as effective as real electronic circuitry. Often, the answer to either or both may be a no. How do you know? Now, the only form of conflict monitoring is usually a single device, the failsafe of conflict monitor, as described in the first item. It seems that some other form of protection from conflicting signals might be in order, either another monitor or better yet a separate interlock device that doesn’t have to do sophisticated monitoring like minimum voltage input, missing reds, yellow duration etcetera, just a simple last ditch monitoring of conflicting greens, just for old times sake, and just in case.

My feeling is, if something can go wrong, it will. I just hate for it to happen on my watch! That’s one reason I’m glad I no longer have a watch.

Bicycle Adaptive Traffic Signal Timing

I’m only an occasional bicycle rider but I have always thought that it would be nice if traffic signals could respond appropriately to the special characteristics of bicycles. Bicycles are different from cars. Among other differences are bicycles do not have air bags nor 5 mph bumpers. Forgetting that though, there are other differences between bicycles and motorized vehicles that need to be addressed. The three most important differences are acceleration, speed and stopping distance. A motorized vehicle can do all three better.

Still, there are good reasons to ride a bicycle. Better fuel economy, good exercise, less pollution, etc. are three very good reasons for riding a bicycle, especially for shorter expeditions.

Many people opt to utilize their bicycles and current rules of the road allow a mix of bicycles and motorized vehicles on the same roads. For many years there were no special considerations given to bicycles. More recently, some signals have installed special bicycle push buttons to provide bicycle timing. This requires the button to be located adjacent to the bicycle path or for the bicyclist to go to the pushbutton sometimes requiring dismounting. Not altogether convenient.

Many agencies made their inductive loop detectors sensitive to bicycles. The MUTCD has even been adjusted identifying bicycle detection requirements. This allows the bicycle to be detected but the timing provided is usually set for motorized vehicles rather than bicycles. There are often also other problems encountered unless special loops are utilized. A loop designed to pickup bicycles often will not detect trucks or SUV and or may detect cars in adjacent lanes causing improper traffic signal timing.

Often, two detector systems are installed in the traffic lane, one to detect bicycles one to detect other vehicles. Obviously this can be a costly method of detection. There are two things that would make things better for bicycles without adversely affecting motorized vehicles. One is bicycle adaptive timing. Adjust the traffic signal green and/or clearance time to be appropriate for the slower bicycle. In order to do this, a good means of detecting bicycles needs to be utilized. It would be better if the same loop detector system could discriminate a bicycle from other vehicles either by the signature of the actuation, amount of actuation, or special loop location.

Obviously, the easiest way is providing a special lane for bicycles that cars don’t travel over. This can be as simple as installing loops in the bicycle lanes. This does require that there is room for the bicycle lane, that bicycles use it and that cars don’t travel over it such as when making right turns.

A better approach is loop detectors that discriminate bicycle actuations from other vehicles. This is possible by providing a different output when the frequency variation of the loop array is low and a separate output or output condition when the actuation is greater. A typical bicycle causes 10-16hz frequency variation while a small car would be over 20 hz variation. Unfortunately, some other considerations need to be made to prevent false bicycle actuations due to cars passing near the loop rather than over it.

A better method would be to utilize an actuation signal signature difference to identify and discriminate bicycles from other vehicles and then provide the individual outputs for each. This should just be an adaptation of the typical counting detector operation. These detectors utilize loop arrays and only provide a single pulse for each vehicle that leaves the loop array. They have accuracies of greater than 98% and should be capable of providing bicycle discrimination with appropriate programming.

OK, now assume we have appropriate detection. Now, we need to adjust the traffic signal timing for the bicycle while still providing the least impact to the other traffic. There are three considerations. A bicycle starts out and accelerates much more slowly than other vehicles, doesn’t go as fast, and doesn’t stop as quickly. A traffic signal typically provides a minimum green time, a green extension time and a clearance time appropriate for the motorized vehicles. If the traffic controller could provide a different minimum green, green extension and clearance time adjusted appropriately for the lower acceleration and speed of the bicycle. Existing formulas can identify appropriate intervals, the key is having a controller that is capable of timing the intervals.

For example, a typical vehicle minimum green might be 6 seconds, green extension might be 3-6 seconds and a clearance interval 4.5 seconds for a roadway with a speed of 35 mph. When adjusted for a bicycle, the minimum green might be 8-10 seconds, green extension 6-10 seconds and the clearance interval of 5-8 seconds.

An important note here is that the vehicle clearance interval consists of both the yellow interval and the all red interval. The yellow interval should not be extended for the bicycle. The all red interval should provide the additional clearance. This is because motorized vehicle traffic could have difficulty responding to varying yellow clearance intervals since most drivers consider it green time and proceed to travel through the intersection on the yellow.

The Naztec model 920 traffic controller provides such timing. Reno A&E evidently has a bicycle discriminating loop detector system available. I haven’t seen the detector yet, but I’m told it exists and is in use.

Obviously, if the discriminating loop detector works, it really opens up adaptive bicycle timing. Even if a controller didn’t have any special timing capabilities, the detector could be set to provide different extension intervals for the two outputs allowing at least a bicycle appropriate green extension interval.

The real benefit of having a controller with bicycle timing capabilities is the ability to provide the extended clearance time for bicycles. At larger intersections, left turn travel distance can reach up to 180 feet. The amount of time it takes a bicycle to travel that distance could be more than 15 seconds. Typically, the motorized vehicle travels the distance in less than 6 seconds. Obviously, good practice doesn’t allow always having the longer interval for bicycles when they are not present.

To sumarize bicycles and other vehicles are different. Different timing needs exist for each. Methods now exist to provide for those differences.

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