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Many motorists know the feeling: The lane they thought would continue straight suddenly becomes left-turn-only, forcing them to make an abrupt lane change. At poorly designed intersections, that moment of confusion can lead to traffic violations, congestion and crashes.

New research from National Yang Ming Chiao Tung University (NYCU) suggests that clearer road design could prevent much of that risk. After an unshadowed left-turn lane at an intersection in Taichung was converted into a fully shadowed design with clear channelization and a gradual transition zone, unsafe driving behaviors fell by 62.3%.

Wrong-lane maneuvers — including through traffic mistakenly entering the left-turn lane and drivers turning left directly from a through lane — dropped by an even more dramatic 94.2%.

When a Through Lane Suddenly Becomes a Turn Lane

Exclusive left-turn lanes are intended to separate turning vehicles from through traffic, helping motorists follow traffic signals and enter the correct lanes safely and efficiently. At many intersections in Taiwan, however, left-turn lanes have traditionally used an “unshadowed” design. In this configuration, the innermost through lane may abruptly become a left-turn-only lane as it approaches the intersection.

Drivers who did not intend to turn are then pressured to change lanes at the last moment or to continue straight from a turn-only lane. The result can be sudden lane changes, traffic violations, congestion and an increased risk of collisions.

Professor Kun-Feng Wu of NYCU’s Department of Transportation and Logistics Management led a research team that examined more than 160,000 vehicle trajectories at an intersection in Taichung.

Using millimeter-wave radar and computer vision technology, the researchers analyzed how motorists behaved before and after the left-turn lane was redesigned. The fully shadowed layout created a clearly separated turn lane with channelizing markings and a gradual transition area, making the road’s intended path easier to recognize. Following the redesign, unsafe behaviors such as abrupt lane changes and crossing double solid white lines declined by 62.3%.

Road Markings That Reduce Mental Strain

A separate study by the team examined whether dotted extensions — guide markings placed in the transition area leading into an exclusive left-turn lane — could help motorists enter the correct lane.