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# Determination of Yellow Light Change Interval at Intersection

## Determination of Yellow Light Change Interval at Intersection

(OP)
Hi all,

I am trying to determine whether certain intersections local to me have yellow change intervals which are calculated "correctly".

For reference, this is in Washington state where the the Revised Code of Washington (RCW) section on yellow change intervals simply points to the MUTCD.

Section 4D.26 of the MUTCD then simply states that the interval needs to be determined using "engineering practices".

Doing some research on my own, I have found this document: NCHRP Report 731 (this is available via google search).

This document gives multiple formulas... a general ITE formula and a kinematic formula. In Appendix A they use it do form the following table:

They also conducted a survey of change intervals in several states, where the average is somewhere around 4.5 seconds, just looking at it (excerpt):

However, the document also discusses another study:

All of the intersections I've timed locally have intervals of 3.5 seconds or less.

So what am I missing? I'm assuming this is pretty nuanced, so is there any other guidance I should be aware of for determining this? Thanks.

Keep em' Flying
//Fight Corrosion!

### RE: Determination of Yellow Light Change Interval at Intersection

I'm not into traffic design, but I suspect the reduced time is to either raise money, by fines, or to make illegal traffic stops. I've sent a copy of this post on to a couple of my lawyer acquaintances for their information. Perhaps they can use the information.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

### RE: Determination of Yellow Light Change Interval at Intersection

(OP)
dik,

Thanks for the response! To be honest I suspect the same thing.

A bigger concern in my area is the fact that our road systems are loaded with photo and video enforced intersections where you are constantly monitored and receive your fine in the mail.

Looking at the regulations, there are very specific requirements a city or town needs to meet in order to operate those camera systems - one of which is that the intersection change intervals need to be in accordance with the MUTCD. If they are too short, there's a good chance the local cities and towns are illegally operating those camera systems and fining people based on non-compliant systems.

Keep em' Flying
//Fight Corrosion!

### RE: Determination of Yellow Light Change Interval at Intersection

That's why I forwarded it to a couple of lawyers... in case they have clients that have problems with this. I quit driving about 5 or 6 years back, so it's not a problem for me.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

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