Traffic Signal Simulation - Is it time for an udpate?

September 19, 2016

There are three observations I’d like to share with the folks in the professional community who are involved in traffic signal coordination, and I’m hoping to hear if others have noticed anything similar.  

First, when implementing coordination plans that have been developed with an optimization model, I often find ways to improve operations during the fine tuning step.  The last step of the process is to input the final timing settings back into the model and run it one last time to get the MOEs for the final settings.  Despite my own on-site observations and travel time run data, the model sometimes outputs MOEs that look worse than the optimization settings that previously came from the model.  

Second, some agencies in my vicinity have been implementing adaptive systems over the last few years.   One agency in particular has a very talented gentleman who has been in charge of signal coordination for many years and is very capable.   My observations are that the operations with the adaptive systems aren’t much better than he used to implement, sometimes even worse.   The part that disturbs me, though, is that when he gets calls to improve traffic flow at a specific location, he response might now be to verify that the adaptive system was working properly on the day in question, then let the caller know he would not be able to produce anything better than the adaptive system.   We have other agencies in the area using a similar response.

Third, in my conversations with people in the general population, it seems pretty clear to me that people waiting to make a minor movement are more patient when there is a lot of traffic moving on the current green phase and can be very impatient when there is no traffic moving at all.   In extreme cases, the model MOE report can indicate a significant improvement even though the verbal public input can be quite negative.  For example, “I had to wait 10 minutes to get through that light today” (even though the cycle length is 150 seconds).


It seems to me we are relying on a set of assumptions in our models (whether off-line or on-line within an adaptive system) that are due for update.   I’d appreciate hearing the experiences of others.   


Pedestrian Hybrid Beacons are coming

June 23, 2016
Also known as a HAWK Beacon, it is a device installed at crosswalks when a regular traffic signal is not appropriate but something more than flashing lights is needed.  Caltrans made a video for people who want to know more.   Go to
to see what might be installed in a city near you in the near future.    
Continue reading...

Mother Nature vs traffic signal pole

March 14, 2016
The Town of Moraga had a very rare occurrence of a sink hole opening up in the same location as a traffic signal pole.   My guess is that the soil around the traffic signal pole gradually washed away until there wasn't enough left to hold up the signal pole any more.   For those that don't know, the foundation for the traffic signal pole is about 9 feet deep and 2 feet around.  For the full story see
Continue reading...

Experimental Pedestrian Safety Device for Signalized Intersections

December 15, 2015
The City of Redding is testing a new type of pedestrian signal head with a yellow outline in an attempt to reduce pedestrian conflicts with right turning vehicles.   See for more information.    Please send a response post if you have direct experience with the trial or trials of other devices with a similar goal.   
Continue reading...

New median barrier on Golden Gate Bridge

January 27, 2015
For those who have not seen it yet, here is a photo of the new median barrier that was installed on the Golden Gate bridge a month ago.  
Continue reading...

New Bicycle Safety Law

October 3, 2014
The Three Feet for Safety act became law in California on September 14, 2014.  It requires drivers to stay at least three feet away from a bicyclist who is moving in the same direction when the driver is overtaking and passing the bicyclist.  The text of the act is now part of the Vehicle Code and can be seen at

The law imposes a $35 fine for drivers who pass too close if the bicyclist is not injured, and $220 if the bicyclist is injured, unles...
Continue reading...

Creative Pedestrian Signal

September 26, 2014
There are signalized pedestrian crossings in many large cities.  Getting pedestrians to take full advantage of the signals and stay safe is often a challenge.  Here is how one US city is being creative:

And here is an alternative from Germany:

Continue reading...

GPS Clocks

September 12, 2014
Question:  How do I tell if a traffic signal controller is equipped with a GPS or satellite clock?
Answer:  The first clue is shown in the photo below.  There should be an antenna on the top of the cabinet, often referred to as a puck because of its shape.  

Inside the cabinet the unit is typically mounted in the back, near the top of the rack, as shown in the photo.  In this case it is a McCain clock unit.  

The black cable connects to the antennae.  The grey cable connects to the controller un...
Continue reading...

Terminal strips

September 4, 2014

Terminal compartments are part of a traffic signal installation that allows circuits to be connected without using splices in pull boxes.  The picture below shows what is inside.  There are two pictures of the same terminal strip, taken from either side.  In the first picture you will see the posts numbered from 1-12.  The posts go all the way through.  In the second picture you can see single wires attached to 6 of the posts.  You can attach up to 3 wires per side, or 6 wires total. 



Continue reading...

Protected Permissive Left Turns

July 16, 2014
Mid-sized and smaller cities have frequently chosen to provide protected left turn phasing on main street approaches of signalized intersections, citing a belief that it provided safer operations.  Recently however, this traditional belief has been challenged for a variety of reasons.  An option that combines protected phasing with permitted phasing emerged and is starting to see deployment.  Also, federal research identified a new approach in the signal display, using a flashing yellow arrow...
Continue reading...
blog comments powered by Disqus

About Us

Steve Fitzsimons If you would like to ask a question about driving rules, traffic signals or street lights, send your questions to: or call 650-314-8313. Steve Fitzsimons is a professional Civil Engineer and Traffic Engineer in California. He is a principal at W-Trans. Find out more about W-Trans at **** If you need a traffic signal design or review, W-Trans is available for hire. If you are an electrical contractor, W-Trans is available for hire to prepare timing plans or traffic control plans.
Make a Free Website with Yola.