ThrU Turns are a type of signalized intersection that helps improve traffic flow for individuals turning left. The basic concept is that the vehicle drives through the intersection, makes a U-turn at a signal that is a few hundred feet past the intersection and then drives back to a right turn off the main roadway.
The concept is similar to that of a driver who is trying to turn left out of a business onto a busy road. Because traffic levels are high, they choose to turn right, make a U-turn and then follow the roadway back. These types of intersection are safer than a typical left-turn, as the chance of a side or "T-bone" crash is greatly reduced.
What is a thru-turn?
The basic concept of the thru-turn has been used for nearly 50 years. The thru-turn is used in urban areas, but is similar to Michigan lefts, downstream U-turns, or J-turns, for instance. Collectively, these are called “alternative intersections.” The driver is prevented from making a direct turn, and needs to follow the highway to a U-turn location and make the turn by heading the other direction.
The common theme is that they are safer. Left turns can be a challenge. They slow down the fl ow of traffic, and in many cases, create the potential for fairly damaging side crashes. When large numbers of vehicles need to turn left, they can back up into through lanes and create congestion and crashes as well. Engineers look for ways to reduce the number conflict points at the intersection (places where there is a chance that one vehicle could strike another). Thru-turns, as well as other similar types of intersections , help reduce right angle or “T-bone” collisions. These are when a vehicle on a side street doesn’t yield to through traffic. These crashes have the highest chance of a fatality or a serious injury. Similar types of alternative intersections currently used in Missouri have also proven to be much safer.
How do they work?
Have you ever tried to turn left out of a parking lot onto a busy road and found it so hard to get a space to make your turn that you turned right and made a U-turn? In many cases it was faster than waiting to directly make a left turn. Thru-turns use many of the same concepts to make a more efficient and safer left turn.
With a thru-turn, drivers wanting to turn left drive through the intersection and make a U-turn at a signalized median crossover. After making their U-turn, they get into the right-most lane and make a right turn. Since they are not in the intersection, other traffic movements are possible
The key element is that the thru-turn may take you a little out of the way, but can help more people make a left turn quicker. In addition, it can also provide more space for left turns in areas where there is limited space before the intersection. There are fewer changes required for the signal at the intersection, which means that engineers can give more time to the through traffic (and get them through the intersection faster too.) The turn is wide enough to handle all traffic, including busses, and can easily handle a large number of cars. Alternative intersections, such as the thru-turn reduce the amount of time that traffic spends waiting for a turn by at least 25 percent. That means that even with the extra distance drivers must travel (maybe a fifth of a mile) they can still get through the turn quicker.
They can also improve the amount of traffic that can get through the intersection by up to 50 percent. This helps reduce the congestion on the through roadway and the cross street during peak traffic periods. It may be a little different, but it is faster and it reduces the wait time at left turns – it’s safer for drivers and for pedestrians. Thru-turns help keep you moving and keep you safer.