What is the justification for a left turn arrow?
Left Turn Signal Phasing - Left turn signal phases facilitate left turning traffic and usually improve the safety of the intersection for left turning vehicles. However, this is done at the expense of the amount of green time available for through traffic and will usually reduce the capacity of the intersection. Left turn arrows also result in longer cycle lengths, which will in turn have a detrimental effect by increasing stops and delays. Pedestrian delays may be increased, resulting in pedestrians ignoring the pedestrian signal.

While phases for protected left turning vehicles are the most popular and most often added phases, other methods of handling left turn conflicts should be considered first. Potential solutions include prohibited left turns and geometric improvements.

Left Turn Phase Criteria - The left turn phase criteria suggested below are a combination of left turning phasing used in several states in the United States and the result of considerable research and study. These warrants are not mandated by the Manual on Uniform Traffic Control Devices (MUTCD) and are provided for information purposes only. Suggested warrants are as follows:
  • Volumes - Consider left turn phasing when the product of left turning and opposing volumes during peak hours exceed 100,000 on a four-lane street, or 50,000 on a two-lane street (one approach lane). Also, the left turn volume for two or more approach lanes should be greater than two vehicles per cycle during the peak hour period. Volumes meeting these levels indicate that a left turn phase may be justified and further study of the intersection is recommended.
  • Delay - Consider installing left turn phasing if a left turn total delay of two vehicle hours or more occur in a peak hour on a critical approach. Also, there should be a minimum left turn volume of greater than two vehicles per cycle during peak hour, and the average delay for left turning vehicle should be at least 35 seconds.
  • Accident Experience - Install left turn phasing if the critical number of left turn accidents has occurred. For one approach, the critical number is four left turn accidents in one year, or six in two years. For both approaches, the critical number is six left turn accidents in one year, or 10 in two years.
Protected / Permitted Left Turn Phasing - Protected / permitted left turn phasing is a left turn movement of traffic at a signalized intersection having a separate left turn phase in the signal cycle to provide a protected green arrow interval, as well as non-protected circular green interval. Use of the protected / permitted left turn phasing technique is based on the assumption that the need for a protected left turn interval has been established. One of the basic precepts of the protected / permitted left turn phasing, is that the protected green arrow is displayed only when needed in a traffic demand condition. It is therefore emphasized that the protected / permitted left turn phasing technique is an efficient concept as opposed to an accident reduction concept although it will probably offer safer operation than permissive only operation.

Protected Only Left Turn Phasing - When a separate interval is provided to accommodate a left turn without conflicting traffic, and left turns are prohibited during the rest of the cycle, protected only left turn phasing occurs. Although the MUTCD provides no left turn phasing warrants, the traffic control device handbook offers suggested guidelines for separate left turn phasing.

Unprotected Left Turn Phasing - Unprotected left turn phasing occurs when an exclusive phase is not provided for left turn vehicles. Left turns are permitted to occur through gaps in the opposing traffic flow. Separate left turn lanes may or may not be provided.

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1. Why do I have to wait so long for a green light on a side street?
2. How do I report a problem with a traffic signal, lane markings, or traffic signs?
3. What should a driver do when approaching an intersection in which the traffic signal is not working?
4. How is the placement of traffic signals determined?
5. What is a Traffic Signal Warrant?
6. What are the Traffic Signal Warrants?
7. What is the justification for a left turn arrow?
8. How do pedestrian signals work?
9. Is it really necessary for me to push a button to activate the pedestrian signal, or can I just wait for the light to change?
10. Why does it always say "don't walk" before I've completed crossing the street?
11. Can I count on a safe crossing if I carefully follow the pedestrian signals?
12. What are the pedestrian rights and responsibilities when walking along or crossing a street?
13. When is a crosswalk unsafe?
14. Do marked crosswalks provide better pedestrian safety than unmarked crosswalks?
15. Why are the words "walk" and "don't walk" being replaced by symbols?
16. What is the roadside clear zone?
17. Why can't we use speed bumps on our block?
18. Are traffic control devices on private property required to meet State standards?
19. What is Florida law in regard to school speed zones and school buses?