LEFT TURN SIGNALS
AND
LANE USE CONTROL

MAKING LEFT TURN INDICATIONS MOVE WITH LANE USE

When lane use control (for reversible lanes) was first introduced, the signal displays were easily adapted to varying lane use. Only the circular red, yellow, and green, and the green arrow were in use. But as the MUTCD developed, it prohibited using the circular red for exclusively protected left turns, prohibited darkening a signal over an unused lane, and specified different signal faces for shared and exclusive turn lanes.

For many years, one of the following was done at signalized intersections within lane-use control:

New developments that will again allow moving indications with lane assignments include:

Only one more development is needed to make this possible: a triple aspect red signal. It is not essential, but makes assigning signal faces much easier.

There are three versions of this signal lens: multiple red lights

The lens has three aspects:

With LED technology, this special red section should be easy to make. It makes the following lane-use control system possible:


TABLE OF LANE ASSIGNMENT

KEY:

Opposing Signals
(upside down)
 

 
Signal Display
as seen by motorist

 
 
Conditions

 
 
Phasings Allowed

 
 
Comments

lane control diagram

1. BALANCED FLOW

  • 2 lanes each direction
  • Center lane left turn
  • Lead-Lag (single-split P/P)
  • Single Lead E/P, P/P, with P
  • Single Lag E/P, P/P, with P
  • Dual Lead E/P, P/P
  • Dual Lag E/P, P/P
  • Dual Split Lead E/P, P/P
  • Dual Split Lag E/P, P/P
  • Split phase (Unsplit Lead-Lag) E/P, P/P
  • Single-split Lead-Lag E/P, P/P
  • Double-split Lead-Lag E/P, P/P
  • Separated Phases E/P, P/P

 

2. BALANCED FLOW

  • 2 thru lanes each direction
  • Center lane left turn
  • Dual Split Lead P/P
  • Single Lead E/P, P/P, with P
  • Single Lag E/P, P/P, with P
  • Dual Lead E/P, P/P
  • Dual Lag E/P, P/P
  • Dual Split Lead E/P, P/P
  • Dual Split Lag E/P, P/P
  • Split phase (Unsplit Lead-Lag) E/P, P/P
  • Single-split Lead-Lag E/P, P/P
  • Double-split Lead-Lag E/P, P/P
  • Separated Phases E/P, P/P

3. UNBALANCED 3 TO 2

  • 3 thru lanes heavy way, 2 thru lanes other way
  • Center lane in heavy direction
  • Each direction's leftmost lane shared thru/left
  • Split phase (Unsplit Lead-Lag) E/P
  • Single Lead E/P, P/P, with P
  • Single Lag E/P, P/P, with P
  • Split phase (Unsplit Lead-Lag) E/P, P/P
  • Single-split Lead-Lag P/P
  • Separated Phases E/P, P/P

Note that a permissive left turn across three or more lanes of oncoming traffic is not recommended.

4. UNBALANCED 3 TO 2

  • 3 thru lanes heavy way, 2 thru lanes other way
  • Center lane in heavy direction
  • Each direction's leftmost lane shared thru/left
  • Lead-Lag (single-split P/P)
  • Single Lead E/P, P/P, with P
  • Single Lag E/P, P/P, with P
  • Split phase (Unsplit Lead-Lag) E/P, P/P
  • Single-split Lead-Lag P/P
  • Separated Phases E/P, P/P

Note that a permissive left turn across three or more lanes of oncoming traffic is not recommended.

5. UNBALANCED 2 TO 1

  • 2 thru lanes heavy way, 1 thru lanes other way
  • Two lane left turn
  • Lead-Lag (single-split E/P)
  • Dual Lead E/P
  • Dual Lag E/P
  • Dual Split Lead E/P
  • Dual Split Lag E/P
  • Split phase (Unsplit Lead-Lag) E/P
  • Single-split Lead-Lag E/P
  • Double-split Lead-Lag E/P
  • Separated Phases E/P

Note that a permissive left turn from more than one lane is not recommended.

A second signal face of thru indications is needed to meet MUTCD requirements. It would be to the right of the rightmost signal face shown, as seen by oncoming traffic.

6. UNBALANCED 3 TO 1

  • 3 thru lanes heavy way, 1 thru lane other way
  • One lane left turn
  • Lead-Lag (single-split P/P, E/P)
  • Single Lead E/P, P/P, with P
  • Single Lag E/P, P/P, with P
  • Dual Lead E/P, P/P
  • Dual Lag E/P, P/P
  • Dual Split Lead E/P, P/P
  • Dual Split Lag E/P, P/P
  • Split phase (Unsplit Lead-Lag) E/P, P/P
  • Single-split Lead-Lag E/P, P/P
  • Double-split Lead-Lag E/P, P/P
  • Separated Phases E/P, P/P

Because a permissive left turn across three lanes is not recommended, the oncoming approach has no permissive left turn.

A second signal face of thru indications is needed to meet MUTCD requirements. It would be to the right of the rightmost signal face shown, as seen by oncoming traffic.

7. UNBALANCED 4 to 1

  • 4 thru lanes heavy way, 2 thru lanes other way
  • Each direction leftmost lane shared thru and left
  • Split phase (Unsplit Lead-Lag E/P)
  • Split phase (Unsplit Lead-Lag) E/P, P/P
  • Separated Phases E/P, P/P

Note that a permissive left turn across three or more lanes of oncoming traffic is not recommended.

A second signal face of thru indications is needed to meet MUTCD requirements. It would be to the right of the rightmost signal face shown, as seen by oncoming traffic.


Signal Operation and Lane Use Change

When the lane use is changed, the signal indications must change with the lane signals in a way to preserve safety.

The following sequence should be used when changing lane use.

  1. For each traffic signal separately, at the next safe changing period, do the following:
    • If necessary, change the phasing to the intersection's transformation phasing.
    • Wait at least 4 minutes after all signals have changed phasing before continuing.
  2. If a lane is being closed to traffic in one direction, do the following:
    • Leave advanced lane-use signals displaying left-turn indications unchanged.
    • Change all other lane-use signals for the closing lanes to yellow X.
    • Wait at least 4 minutes before continuing.
  3. If any lanes have yellow X indications, do the following on approaches losing lanes:
    • For each traffic signal separately, at the next safe changing period, do all of the following simultaneously:
      • Change the advanced left-turn lane-use signal to yellow X.
      • Change signal faces for those lanes to the new signal face assignments.
    • After the last change happens, wait the designed yellow X lane clearance period.
  4. Do the following:
    • Change all yellow X indications to red X.
    • Change down green arrows to white left-turn arrows where needed.
    • Change signal faces for those lanes to the new signal face assignments.
    • Wait the designed red-X lane clearance period.
  5. For each traffic signal separately, at the next safe changing period, do all of the following simultaneously:
    • Change all lane-use signals to the new configuration.
    • Change all signal faces to the new signal face assignment.
    • Wait at least 4 minutes after the last change of signal face assignment.
  6. For each traffic signal separately, at the next safe changing period, do all of the following:
    • If necessary, Change the signal phasing to the new configuration phasing.

The important part of this is to not send any vehicles in a lane into signals that are not ready for them.

lane control diagram

Animation Key:

  1. Red clearances are not shown.
  2. All times are speeded up except flashing yellow arrow flash rates.
  3. Only one signal cycle is shown between changes, constituting the delay periods mentioned.
  4. The numbers during the all red periods correspond to the numbered list at left.
  5. B means using or heading to balanced flow.
  6. U means using or heading to unbalanced flow.

If the Triple-Aspect Red Section is not Available

What can be done before the FHWA allows a multiple aspect red section? The problem is twofold:

The difference between the circular red and the red arrow:

The difference between the other red indications and the red X


NOTES


* The standard phrases in use violate the rules in English for placing the word "only," or lack clarity.

The word "only" always modifies the word AFTER it (never the word before it). "Only" is NOT an adverb, so it does not follow the verb. The following table shows the wrong phrases, and their proper replacements:

MUTCD phraseReplacement

protected-only

exclusively protected

permitted-only

exclusively permitted

dual arrow

dual color arrow

LEFT TURN ON ARROW ONLY

LEFT TURN WAIT FOR ARROW

LEFT TURN ONLY

MUST TURN LEFT

LEFT TURN ONLY THIS LANE

LEFT LANE MUST TURN LEFT

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