Opinion: Confusing left turns – Too many choices

Doug Dahl of The Wise Drive explains the complexities of multi-lane left turns, highlighting how traffic engineers use lane extensions to guide drivers and improve intersection efficiency.

Doug Dahl addresses a question about what’s the right way to turn left?

Q: I drive through an intersection, almost daily, that has two left-turn lanes, while the cross-street they turn into has three lanes. There are some dots curving through the intersection that seem to suggest that the inside left-turn lane can choose from the two leftmost lanes, and the outside left-turn lane should go to the furthest right lane. But the markings aren’t clear and from the behavior of other drivers it’s obvious that many of them don’t agree with me. What’s the right way to turn left here?

A: The simple and obvious answer is … just kidding; how about a tricky and possibly unsatisfying answer? But as a warmup, let’s consider an intersection with a single left-turn lane. The law requires drivers to approach and complete the turn “in the extreme left-hand lane lawfully available to traffic.” Or as the Washington Driver Guide says, “Turn from the lane that is closest to the direction you want to go and turn into the lane closest to the one you came from.” Simple, right? You already knew that.

Once we bump up to two designated left turn lanes, well, neither the law nor the driver guide explicitly describes how to proceed, but a reasonable interpretation, and what most of us were probably taught in driver’s ed, is to stay in the lane you started in. For your intersection, a driver in the leftmost turn lane would continue in the left lane of the roadway being entered. A driver in the other turn lane would continue in the center lane. That would leave the right lane empty, which seems like we’re underutilizing the roadway.

But you had to make it complicated by adding that there are dots curving through the intersection, called line extensions by traffic engineers. You’ll often find extension lines at non-traditional intersections where the expected vehicle movements aren’t immediately clear, like in a five-way intersection.

As you described in your intersection, the extension lines appear to give the leftmost turn lane the left and center lanes of the road being entered, while the other left-turn lane is guided to the right lane. Why would a traffic engineer do that? At a busy intersection, who gets which lane might be determined by analyzing traffic flow and assigning lanes based on what moves the move vehicles through the intersection the most efficiently.

When an engineer designs an intersection they rely on standard resources such as the Manual on Uniform Traffic Control Devices and the Washington DOT Design Manual, but there aren’t models for every possible design so they also take into consideration the unique characteristics of the specific intersection. Most intersections aren’t actually all that unique and they conform to our expectations. Some though, by either necessity or practicality, diverge from the norm, and lane extensions are one tool engineers use to guide drivers through. The incomplete answer then is yes, you’re right.

However, you mentioned that other drivers don’t seem to understand it the same way. Whether it’s because the line extension paint is wearing away and hard to see, or drivers aren’t even looking and just relying on what they’ve always done, when two drivers are in the same intersection operating on two different sets of rules there’s the clear potential for conflict.

So you’re right in your interpretation of the lane extension markings, but you’re even more right if you prioritize avoiding a crash over exercising your lane options. It sounds like you’re on the right track already: Use the markings to inform your route while staying aware of risks from other (possibly less-aware) drivers.

The Wise Drive is hosted by Doug Dahl, a Target Zero manager for the Washington Traffic Safety Commission.

Doug Dahl addresses a question about what’s the right way to turn left?

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