Traffic Signal Phasing Diagram

This month’s blog post focuses on instances where a driver is involved in a car accident that was not their fault, and then the other driver tries to blame the car accident on them!  When we receive calls from people in car accidents that are going through this unfortunate experience often their first question is, “what can we do?” Generally, there are many ways to address a situation where the other driver in a car accident tries to wrongfully shift the blame. Sometimes, you may have photographs of the damage to each vehicle which just do not line up with the other driver’s story.  Other times, there are people who independently witness a car accident and can corroborate your side of the story. However, some car accidents simply have no witnesses or other evidence that can help.  In such cases, fault often becomes your word versus theirs. In car accidents such as these, an accident reconstructionist may be able to provide the evidence that’s needed.  The remainder of this post describes what exactly an accident reconstructionist is, and how we utilize their expertise to prove which driver in a car accident was at fault.

So, what exactly is an accident reconstructionist? An accident reconstructionist is simply put, an expert at vehicular accident reconstruction.  Vehicular accident reconstruction is the scientific process of investigating and analyzing the available information from a collision in order to form a conclusion regarding the cause of a car accident. Accident reconstructionist undergo training and take many courses so that they can become proficient at subjects such as: kinematics, work-energy methods, and conservation of linear momentum. These courses of education allow the accident reconstructionist to not only determine who may have been at fault for a collision, but also things such as the speed of the vehicles at the time of the car accident.  Often when a car accident occurs in an intersection, one of the first pieces of evidence an accident reconstructionist will exam is a traffic signal phasing diagram.

Signal phasing diagrams have been instrumental in assisting juries come to a determination as to which driver is at fault in a car accident.  An example of such a scenario is as follows:

Example: It is early morning and a driver (Driver 1) is proceeding down a main road in Seal Beach, CA.  On this Seal Beach road, Driver 1 notices that all the lights in front of him are green. Driver 1 proceeds towards the intersection of a cross street.  At the same time, another driver (Driver 2) is traveling down a cross street on his way to work. As Driver 2 approaches the intersection of the well-known road, he has nobody in front of him and believes he sees a green light to proceed.  The two drivers unaware of one another, enter the intersection at the same time and collide in a violent “t-bone” car accident.  Both claim they had a green light.  So which driver is at fault?  At trial, an accident reconstructionist tells the jury that he was able to obtain a traffic signal phasing diagram for the intersection from the city of Seal Beach. The reconstructionist then states that based on his review of the phasing diagram, the main road was set to always have a green light at that time of day – unless traffic from the cross street indicated another car needed to cross.  For the cross street to have a green, a driver on the cross street would need to drive over the road loop at the entrance of the intersection, wait three seconds for the light to change from red to green, and then could proceed. Therefore, based on Driver 2’s testimony that prior to entering the intersection there was nobody in front of him, it was impossible that his light was always green as he described.  A jury is then able to use this information and conclusively determine that Driver 2 ran the red light.  Driver 2 was therefore negligent and responsible for Driver 1’s injuries.

Without the aid of an accident reconstructionist in the above-mentioned example, that situation would be nothing more than “he said she said” and justice may be lost

As is apparent, an accident reconstructionist can be vital to a car accident case where two drivers each claim the other was at fault.  Sometimes if a car accident results in serious injuries or death, a local police force may employ a trained accident reconstructionist to investigate the scene. However, often times only an untrained officer responds to the scene and creates a basic traffic collision report. In the latter situation it may become necessary to retain the services of your own accident reconstruction expert in order to prove your case.

What is important to remember is that if you’ve been involved in a car accident and the other driver wrongfully claims that you caused the car accident, do not give up hope, there may be another way to prove who is at fault!


The information contained in this post is for general information purposes only. Nothing on this post, or website, should be taken as legal advice for any individual or case situation. This information is not intended to create, and receipt or viewing does not constitute, an attorney-client relationship.  For a free consultation please reach out to our attorneys to arrange a time to discuss your case.


Seal Beach Personal Injury Law office

We are excited to announce the opening of our newest law office located in Seal Beach at 201 8th Street, Ste. 100, Seal Beach, CA 90740.

Not only will this office serve as our new “home” office, but it will be the primary office used to assist those involved in car accidents in Seal Beach, Huntington Beach, Long Beach, and our surrounding community.  We can’t wait to make a positive impact and become a part of the fabric of Seal Beach’s small business community.  If you have been involved in a car accident, wish to participate in a beach cleanup, or just want to enjoy the summer concert series at the pier with your neighborhood lawyers, we hope you will drop by and take a look at our new space!

For anyone involved in a car accident or looking for legal advice, our Seal Beach office will be open Monday-Friday from 8 a.m. – 6 p.m., and we can be reached for emergencies on the weekend at any time by email.  We can’t wait to meet you all!