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)  
1.  For the mathemathical proofs and the physics  behind this spreadsheet, see Short Yellows and Turns:  
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:  
13.  For details on ITE's Derivation of the Yellow Light Interval Equation:  
14.  This spreadsheet does not consider the obsolete unsafe practice of including the all-red clearance interval with the yellow duration.     The numbers above are just yellow times.    One would  add more time if the yellow included the all-red clearance interval.