Turn left at the intersection

Over 60% of traffic collisions at intersections involve a left turn. Some US cities, including Salt Lake City in San Francisco and Birmingham, Alabama, have restricted left turns.

Dr. Vikasugaga, professor of civil engineering at Penn State and interim director of the Larson Transportation Institute, discusses how a left turn at an intersection can cause an accident, worsen traffic and use more gas.

How dangerous is it to turn left at an intersection?

Gaya: When you turn left, you have to cross opposing traffic. If there is green light, you will need to wait for a gap in an oncoming vehicle before turning left. If you accidentally judge when you decide to turn, you can hit opposing traffic or bump into it. It’s an angle crash and one of the most dangerous types of crashes.

Also, drivers of vehicles on the left usually see opposing traffic. However, it is possible that pedestrians are crossing a street with on. In many cases, drivers do not see pedestrians, which can also cause serious accidents.

On the other hand, the right turn must join the traffic, but it is not directly conflicted with the traffic. Therefore, a right turn is much safer than a left turn.

What are the statistics on the unique dangers of turning left?

Approximately 40% of all crashes occur at intersections. 50% of these collisions are seriously injured and 20% are fatal.

Approximately 61% of crashes at intersections involve a left turn. The left turn is generally the most frequent movement at intersections, so there are plenty of 61%.

Why is a left turn inefficient for traffic flow?

They can block other lanes from moving when the left-direction vehicle is waiting for a gap, especially when some vehicles are waiting to turn left.

Instead of green light, many intersections use green arrows to move left-turning vehicles. But to do that, all other movements at the intersection must cease. Stopping all other traffic just to provide some left turn will reduce the efficiency of the intersection.

Also, every time you move to another “phase” of traffic, like the green arrow, there is a short period of time when all the lights are red at the intersection. Transportation engineers call it all red time. That’s when the intersection is not offering vehicles. The total red time is 2-3 seconds for each phase change, and that wasted time quickly increases, further reducing the efficiency of the intersection.

What restrictions are being tested in different cities?

If Downtown is not very busy during off-peak periods, it’s fine to allow left turn. This is because there is no need for additional ability to move the vehicle at each intersection.

Some cities have implemented signs that will not change to the left at the peak afternoon period of intersections from 7 to 9. This is the peak afternoon period. In San Francisco, for example, Vanness Avenue limits left turns during peak periods.

However, cities are not enforcing these restrictions on a large scale. If possible, there are restrictions along individual corridors and isolated intersections, rather than essentially the whole of downtown. This will make the downtown street network more efficient.

Roundabout is one approach to avoid a left turn.

Roundabouts are safe as you no longer have to cross the traffic on the other side. Everyone cycles in the same direction. Find where you need to go and then finish.

However, in general, limiting left turns is more efficient. Roundabouts are not that efficient when you’re busy. The roundabout can fill up, causing gridlocks, and the vehicle cannot move. Traditional intersections do not tend to be bastards.

Roundabouts also take up more space. Installing a roundabout can mean expanding the intersection. In some downtowns, this means demolishing buildings or removing sidewalks. To limit left turns, you need the symbol “turn left” or “do not turn left during peak period.” that’s it.

What are the benefits of banning left turns in urban areas?

If you cut it, eliminating a left turn will increase the travel distance. You will need to travel a long distance to get to where you need it. The worst case scenario is to circle the block. I’m actually traveling four extra blocks lengths to get to where I need to go.

However, not all trips need to circumvent the block. In a typical downtown, each trip is on average about one block long. That’s not an extra distance. And that extra driving is offset by the fact that each intersection with a prohibited left turn drives more vehicles. That means, every time you’re at an intersection, you average less time. So you’ll travel a little longer, but you’ll reach a faster place.

Does avoiding a left turn improve fuel economy?

Our study found that vehicles travel on average longer distances with limited left turn, but do not stop much at intersections, thus fuel costs less (15% to 15% less).

This is why UPS and other fleets route vehicles to avoid left turn. Less idling and fewer stops.

Do you think it would be widely accepted to ban left turns?

It’s a new strategy, which makes it uncomfortable for some people. But I think when they reach their destination faster, people will latch onto it.

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