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Using this progression calculator

• Learn about traffic signal progression.
• Learn about the mathematics used on this page.
• Operation:
  1. Collect your data. Get operating speeds, distances between intersections, and signal conditions.
     You can click the SAMPLE button to enter marginal sample data to try out the page.
     You can click the ACTUAL button to enter actual data from a real location to test it out.
     See if you can do better than either.
  2. Click to select the measurement system that your data are in.
  3. Decide which end of your street has the reference signal. Call it the "toward end."
  4. Call the other end of the street the "away end."
  5. Start entering data with the reference signal at the top.
  6. Enter the name of each CROSS STREET in the table. If you have fewer than 15 cross streets, leave the bottom ones blank.
  7. Enter each operating SPEED between intersections in the spaces provided.
  8. Enter each DISTANCE between cross streets in the spaces provided. Enter 0 in the spaces below the last cross street.
  9. Enter the TYPE allowed for each signal. Use one of these methods for each signal:
     • Sum the numbers of these 4 types listed that the intersection design permits, and enter the sum under TYPE:
       • 1 - Normal - Both directions have simultaneous green lights
       • 2 - Lead-lag - Lead-lag left turn phasing can be used - Make sure the signal indications do not cause yellow-trap
       • 4 - Split-phase - the opposing directions don't have greens at the same time, but in consecutive intervals
       • 8 - Dual-green - The light turns green twice in one cycle
       • To give the computer free reign, enter 15.
     • Use one of these special types for special conditions:
       • -1 - Route turns - The main route makes a turn at this intersection, so different phases serve each direction.
         • If the right turn on the route is a free movement, choose a half signal (below) instead.
         • Use route turns if the street begins as the stem of a T-intersection.
         • Use route turns if the signal has a clockwise diamond interchange sequence, or is a diverging diamond interchange.
       • -2 - Half-away - The signal does not stop traffic moving from the bottom of the list to the top of the list.
       • -3 - Half-toward - The signal does not stop traffic moving from the top of the list to the bottom of the list.
       • To progress a one-way street, set all of the signals to half-away.
       • To progress a pair of one-way streets, do this procedure:
         1. Select half-away for the minor streets, and get the offsets for the street that is one-way away.
         2. Select half-toward for the minor streets, and get the offsets for the street that is one-way toward.
  10. Enter the SPLIT for each signal. This is the fraction of time the signal takes servicing the progressed street.
      Enter the GREEN period for each signal. This is the fraction of time the thru signal is green in one direction on the progressed street.

      Signal Type	TYPE Value	SPLIT Value	GREEN Value
      One phase for the street	1	Fraction of cycle for street	Fraction of cycle for street
      Dual lead or dual split lead	1	Fraction of cycle for street	Fraction of cycle for thru
      Dual lag or dual split lag	1	Fraction of cycle for street	Fraction of cycle for thru
      Dual lead-lag or Double-split lead-lag	2	Fraction of cycle for street	Fraction of cycle for thru
      Split-Phase (Unsplit lead-lag)	4	Fraction of cycle for street	Fraction of cycle for one direction
      Dual green (two greens per cycle)	8	Fraction of cycle for street	Fraction of cycle for one green
      Auto selection among the above	15	Fraction of cycle for street	Fraction of cycle for one thru time
      Progressed Route turns at intersection	-1	Fraction of cycle for route left turn	Fraction of cycle for route left turn
      Half signal stops away direction	-2	Fraction of cycle for away green	Fraction of cycle for away green
      Half signal stops toward direction	-3	Fraction of cycle for toward green	Fraction of cycle for toward green
      Diverging Diamond signals (treat as one signal)	-1	.5	.5

  11. Select one of these methods of operation to start the calculation:

      Wanted Operation	Wanted Info					Start Button	Data Needed						Notes
      	C Y C L E L E N	G R P O F F S E T	S I G O F F S E T	H A L F C Y C L E S	B A N D W I D T H		C Y C R A N G E	C Y C L E L E N	G R P O F F S E T	S I G O F F S E T	S I G I N F O	R O A D I N F O
      Find optimum progression	√	√	√	√	√	AUTO	√	√	√	Finds cycle length, offset, and signal settings
      Optimize given cycle length	√	√	√	√	FIND	√	√	√	Finds offset and signal settings
      Get signal settings for plan	√	√	√	CALC	√	√	√	√	Finds signal settings
      Analyze existing signal settings	√	√	TRY	√	√	√	√	√	Finds bandwidths
      One-way progression two-way street part 1	√	√	√	√	√	AUTO	√	√	√	Set all to Half-Away or all to Half-Toward
      One-way progression two-way street part 2	*	*	*	√	√	TRY	*	*	*	*	*	*	Set signal Type and Mode to actual settings;

      * Provided or calculated in part 1.
      SIG INFO includes Type, Split, and Green
      ROAD INFO includes Cross Street, Speed, and Dist.

      • Enter a cycle length between the CY buttons, and then click FIND.
      • Enter a range of cycle lengths to try on the top line, and then click AUTO.
      • Enter the cycle length between the CY buttons and the offset between the OS buttons, and then click CALC.
      • Adjust the generated cycle length with the CY buttons and the offset with the OS buttons, and then click CALC.
      • Enter offset values in the table too (or adjust previously generated ones), and then click TRY. Tests existing progression.
      • To test unbalanced progression, Enter Types of Half-Away or Half Toward. Use AUTO to find offsets.
        Then enter real signal types in both Type and Mode and click TRY.
• Results:
  1. half-cycles - This number contains two important values needed to adjust the progression to fit:
     • The fractional part of the left number indicates how far from the crossing point the intersection is.
     • The whole number on the right indicates which crossing point the intersection should use.
  2. offset - The time, as a fraction of a cycle, of the center of the green interval.
     • All offsets are between 0 and +1. They represent how much past the system reference time the center of the green interval is.
     • The offset of a lead-lag signal is for the center of the combined lead, thru, and lag periods.
     • The offset of a split-phase signal is for the center of the combined lead and lag periods.
     • The offset for a dual green is for the away direction. Add or subtract .5 for the toward direction offset.
     • The offset where a route turns is for the away direction. Add or subtract .5 for the toward direction offset.
     • The offset for a half signal is the offset for the direction the signal controls.
  3. mode - Indicates the computer's selection of the type of traffic signal cycle to use. Uses type values listed above.
     • 
       The background colors indicate the following:
       1 - White: The signal is normal, dual lead, or dual lag.
       2, 4 - Blue: The away direction leads and the toward direction lags (lead-lag or split-phase).
       2, 4 - Red: The toward direction leads and the away direction lags (lead-lag or split-phase).
       8 - Amber: The signal is dual-green.
       -1 - Violet: The route turns at the signal.
       -2 - Dark blue: The signal is a half signal stopping the away direction.
       -3 - Dark red: The signal is a half signal stopping the toward direction.
  4. a-band - Progression band at the signal in the away direction.
  5. t-band - Progression band at the signal in the toward direction.
     • Band centers not checked - Shows the thru band width for each signal, as a fractional part of the cycle length.
     • Band centers checked - Shows the centers of the thru band at each signal, as an offset.
     • To change this display, without changing other values, click the check box, and then click TRY.
     • 
       The background colors for band values indicate the following:
       - White: This signal has bandwidth to spare.
       - Blue: This critical signal limits the leading edge of the thru band in this direction.
       - Red: This critical signal limits the trailing edge of the thru band in this direction.
       - Orange: This critical signal limits both edges of the thru band in this direction.
  6. suggestions - Choose the function of this column with the Band radio buttons:
     • advice - Shows any suggestions the computer has for improving the thru band.
       * An asterisk refers to longer suggestions to be found in the message window.
     • edges - Shows the leading and trailing edges of the thru band.
     • sides - Shows the leading and trailing sideband widths of the thru band.
     • These number sets are in the following order: lead away, trail away, lead toward, trail toward.
     • To change this display, without changing other values, click the radio button, and then click TRY.
  7. Computed band: away - Entire progression bandwidth in the away direction.
     Computed band: toward - Entire progression bandwidth in the toward direction.
• Improving the bandwidth - suggestions:
  1. Increase the split. This may not be possible at critical locations.
  2. Remove a signal, or set it to flashing at certain times.
  3. Change the speed of a portion of the street.
  4. Reconfigure the signal to allow lead-lag or split-phase operation.
  5. Prohibit some movements at the intersection (can change an intersection into two half-signals)
  6. Divert traffic from the cross street to other cross streets.
  7. Install a free right turn where the route turns.
• Glossary:
  • Away - The direction of motion from the top to the bottom of the list of signals. Applies to only this page. Antonym: Toward
  • Cycle Length - The amount of time it takes the traffic signals in a progressed system to complete one cycle of all phases.
  • Dual-green - A signal sequence where the same green light appears twice in a signal cycle. Can also refer to a signal operating at half the cycle length of the other signals.
  • Half-Away - A signal that stops traffic moving in the direction from the top to the bottom of the list of signals, but does not stop traffic in the opposite direction. Applies to only this page.
  • Half-cycle - Half of the time taken for one cycle, or one of the nodes where perfect progression exists. These nodes exist at distance intervals corresponding to the distance traveled in one half-cycle.
  • Half-signal - A signal that stops traffic moving in one direction, but does not stop traffic in the opposite direction. Applies to only this page.
  • Half-Toward - A signal that stops traffic moving in the direction from the bottom to the top of the list of signals, but does not stop traffic in the opposite direction. Applies to only this page.
  • Lag - A left turn phase that immediately follows the oncoming straight-ahead phase. Beware of yellow-trap.
  • Lead - A left turn phase that immediately precedes the oncoming straight-ahead phase.
  • Lead-Lag - A signal sequence with a leading left turn in one direction, and a lagging left turn in the opposite direction. Beware of yellow-trap.
  • Mode - The kind of signal operation chosen by the computer. Applies to only this page.
  • Offset - For this page, the location in time of the center of the green interval, relative to a fixed point in the signal cycle.
  • Phase - The part of a signal cycle when one particular signal is green, plus its clearance period.
  • Split - The fraction of the signal cycle when the signal on the progressed street is green.
  • Split-phase - A signal sequence where one direction has a completely separate interval immediately before the interval for the opposite direction.
  • Thru Band - The fraction of the signal cycle when traffic can flow freely without stopping.
  • Toward - The direction of motion from the bottom to the top of the list of signals. Applies to only this page. Antonym: Away
  • Type - The kinds of signal operation permitted at an intersection. Applies to only this page.

Links:

• Learn about traffic signal progression
• Learn about the mathematics used on this page.
• Do you understand yellow-trap?
• Definitions
• A visual example of flashing yellow arrows
• Signal Phasing Table
• Common traffic fallacies
• Creepy drivers don't get green lights sooner
• Traffic hazards and solutions
• HOME