







Yellow
Change Intervals for Straight and Turning Movements

















AASHTO

ITE


Turns













Perception Time (s)


1.5

1.0















Decleration (ft/s2)


11.2

10.0




Critical












t = Z  y

t  ts

Critical


D



Distance

Dilemma



Vf

tb

b

s

ts

Z

y

Time from

Elapsed Time

Distance &


Dilemma



& Dilemma

Zone End

Dilemma

Effective


Intersection

Deceleration

Distance

Distance Before

Time Transpired

Time to

Actual

Critical Distance

Since Driver

Dilemma

Dilemma

Zone



Speed Limit


Minimum

Actual

Braking

Stopping

Braking

Zone Start

(feet from

Zone

Deceleration


Entry Speed

Time

Travelled While

Driver Applies

Till Braking

Traverse Critical

Turn Yellow

to Dilemma

Began Braking

Zone Start

Zone Length

Ends (feet from


Approach Name

(mph)

Grade (%)

Yellow Duration (s)

Thru Yellow (s)

Time (s)

Time (s)

Distance (ft)

Distance (ft)

intersection)

Length (ft)

(a + Gg)


(mph)

(s)

Decelerating (ft)

Brake (ft)

(s)

Distance (s)

Time (s)

Zone End (s)

(s)

Distance (ft)

(ft)

intersection)















































































































































































































































































































Notes:





1. For the mathemathical proofs and the
physics behind this spreadsheet, see Short Yellows and Turns:

http://redlightrobber.com/red/links_pdf/ShortYellow.pdf


2. Where you see red is a condition where ITE
forces a driver to run a red light.


3. When the light turns yellow, ITE forces
drivers between the start and end of the dilemma zone to run the red light.




















6. Sometimes the end of the dilemma zone is
farther from the intersection than the start. That means there is a region on the road
where the driver can choose to stop or go and either is good.


7. Grade = rise/run * 100.0. Grade is a percent. Positive grades are inclines. Negative grades are declines.


8. The yellow duration is always the peception
time + half the time it takes for a car to brake. Note that you can never stop your car
within the time the light is yellow.


9. This spreadsheet uses ITE's equation for
yellow light durations. The equation
embeds Newton's Laws of Motion.
Therefore by the laws of the universe, no yellow light duration can be
set less than these values. If less,
then the yellow duration is illegal by the Canute Rule.


10. ITE's equation does not handle grades
greater or less than 10 percent. It
does not work in hilly places like San Francisco. This is because ITE's equation invokes
small angle approximation formulae.


11. ITE's equation does not handle slippery
roads. ITE's equation does not handle
coefficients of friction.


12. Even with properly set yellow durations,
ITE's equation always guarantees a steady flow of cars running red
lights. See Dilemma
Zone:


http://redlightrobber.com/red/links_pdf/DilemmaZone.pdf


13. For details on ITE's Derivation
of the Yellow Light Interval Equation:

http://redlightrobber.com/red/links_pdf/Derivation.pdf


14. This spreadsheet does not consider the
obsolete unsafe practice of including the allred clearance interval with the
yellow duration. The numbers above
are just yellow times. One
would add more time if the yellow
included the allred clearance interval.

