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The volume requirements are calculated using a formula, according to Valerie Holmes, assistant city engineer for traffic for the city of Greenville. The number of left turn vehicles is multiplied by the number of opposing through and right turn vehicles at a particular intersection. If that number meets or exceeds the minimum of 50,000 per lane, then the intersection is eligible for a designated turn signal.

While those dedicated signals would make it easier for drivers to take left-hand turns, there's more to it than the city or South Carolina Department of Transportation simply deciding to put a designated left turn signal at every light. In fact, those decisions are not entirely up to those departments. They're subject to federal guidelines regarding traffic volume. Decisions also require consideration of where turning vehicles would wait and how adding a left turn signal phase might affect backup in the area.

Do you have a question you want answered? Send it to elafleur@greenvillenews.com or contact Elizabeth on her Facebook page at facebook.com/ElizabethSLaFleur. Answers will appear in the Tuesday and Friday print editions of The Greenville News.

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Intersections in Greenville's city limits are handled by the city of Greenville's traffic division. Those in the county are handled by DOT. No matter if an intersection is located in the city or county, it must meet the minimum traffic volume requirements as laid out by the federal government before being considered for a designated left turn signal.

How long must you indicate before turningleftor right

Intersections also need to have space for "vehicle storage" in order to be considered for a designated left turn signal. This means a dedicated lane where cars are held while waiting to turn.

I've wondered about left turn signals while waiting to turn left at an intersection as car after car passed straight through and the signal turned from green to yellow to red.

How long must you indicate before turningleftor right NSW

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"If there are not left turn lanes on any of the intersecting roads you cannot put a left turn phase on the signal," said Pete Poore, director of communications for DOT. "Or if the left turn counts do not warrant a left turn phase, we don’t add one."

"This results in less green time for the mainline and increased backups," Holmes said. "So we have to be judicious in determining where a turn arrow is installed."

Residents interested in requesting the addition of a designated left turn signal can contact DOT or the city of Greenville Traffic Engineering Department — or just practice patience when taking left turns.

Beyond the basic requirements, Holmes adds that a designated left turn signal requires taking green time from another phase of the intersection signal to accommodate that movement.

Question: Why doesn't every city and county intersection with a traffic light have a dedicated left turn signal? - Peter MacKinnon

Just like the city of Greenville, DOT must take into account federal guidelines regarding traffic volume and whether there is already a designated lane for left turns before deciding to place a designated turn signal.

Answer: If there's one thing I've learned since starting this column less than two weeks ago, it's that the Upstate loves to talk about roads. Dozens of you have filled my email inbox with questions — I'm happily working to answer them, by the way — and the majority of those questions are related to traffic and roads.