Reverse Variable Left-Turn Lane: An Innovative Practice in Optimizing Urban Traffic Time-Space Resources

The Reverse Variable Left-Turn Lane is an innovative traffic design that dynamically reconfigures exit lanes for left-turn use during specific signal phases. This time-space optimization strategy significantly enhances intersection capacity without costly construction, offering an efficient solution for urban left-turn congestion management.

With accelerated urbanization and continuous growth in vehicle ownership, the contradiction between supply and demand for urban road resources has become increasingly prominent. At intersections, which are critical nodes of traffic congestion, how to improve traffic efficiency through refined design has become a key issue in traffic management. As an innovative traffic organization model based on in-depth utilization of time-space resources, the reverse variable left-turn lane dynamically adjusts lane functions, significantly enhancing left-turn capacity without increasing physical space, offering new solutions for urban traffic management.

I. Definition and Core Mechanism of the Reverse Variable Left-Turn Lane

The reverse variable left-turn lane refers to a special lane set on the inner side of the exit approach at an intersection, whose function switches dynamically with signal phases: during the left-turn phase, it serves as a left-turn lane, allowing vehicles to "borrow" the opposing lane to wait for left turns; during the through phase, it reverts to its function as an exit lane. This design applies the principle of time-space reuse, converting idle exit lane space into temporary storage for left-turning vehicles, thereby improving overall intersection efficiency.

Its core advantages include:

Efficient use of time-space resources: Dynamic lane function switching maximizes the utilization of intersection space.

Flexibility to adapt to traffic flow: Lane allocation can be adjusted based on real-time traffic demands, alleviating imbalances between left-turn and through traffic.

Low-cost modification: Requires only minor adjustments such as markings, signals, and guidance facilities, without large-scale construction.

II. Application Scenarios and Conditions

The reverse variable left-turn lane is suitable for the following scenarios:

Prominent conflict between left-turn demand and space: Intersections with high left-turn volumes and secondary queuing, where road width limitations prevent additional left-turn lanes.

High through traffic volume: Through lanes are already at capacity, and no space can be reallocated for left turns.

Irreconcilable time-space resource conflicts: Limited intersection space with high opposing through traffic, requiring refined organization to balance left-turn and through movements dynamically.

Its implementation requires the following conditions:

The approach already has a dedicated left-turn lane and an independent left-turn signal phase.

The intersection exit has ≥2 lanes to ensure lane function switching does not affect other traffic flows.

Sufficient internal intersection space to meet the minimum turning radius for left-turning vehicles.

No other options are available for adding left-turn lanes.

III. Technical Implementation and Optimization Strategies

The implementation of the reverse variable left-turn lane requires coordinated efforts in hardware modifications and signal control:

Hardware Modifications

Add an opening on the inner side of the exit lane, using colored markings to define the lane range. The length should be scientifically determined based on the left-turn phase green ratio and vehicle queue length.

Install complementary guidance displays and signals to indicate lane status in real time (e.g., "Left-Turn Borrowing," "No Entry").

Optimize the opening position to allow early U-turns, reducing U-turn vehicle interference with left-turn lanes, or implement U-turn restrictions based on actual traffic conditions.

Signal Control Optimization

Adjust the signal phase sequence to "left-turn first, then through," ensuring left-turning vehicles can queue in the variable lane during the preceding through phase and pass quickly once the left-turn phase begins.

Install dedicated signals for the variable lane, synchronized with main signals to avoid conflicts.

Dynamically adjust phase timing based on variable lane length and vehicle passage efficiency to ensure efficient queuing and clearing.

IV. Practical Cases and Promotion Results

In May 2012, Jinan traffic police first proposed the concept of the "reverse variable left-turn lane" and implemented it at the east entrance of the Jingshi Huanshan intersection, marking the first such lane in China. The model has since been promoted to over 40 locations in Jinan, including Jingshi Road and Huayuan Road.

In November 2015, Shenzhen traffic police implemented "borrowing lanes for left turns" at the Huanggang Sungang intersection, later promoting it at eligible intersections citywide with optimized safety facilities to alleviate left-turn congestion.

In November 2021, Tianjin traffic police officially launched the "reverse variable lane" at the intersection of Second Avenue and South Sea Road in the Binhai New Area, using dynamic borrowing of opposing lanes to ease peak-hour left-turn pressure.

The application of the "reverse variable left-turn lane" requires scientific traffic flow analysis and should not be treated as a universal solution. It is unnecessary in scenarios with insufficient left-turn volume, inadequate intersection space, or large vehicle traffic.

Its promotion achievements include:

Significant improvement in traffic efficiency: Dynamic lane allocation alleviates conflicts between left-turn and through traffic.

Low construction costs: Single-point modification costs are only 1/5 to 1/10 of traditional road-widening projects.

Strong adaptability: Designs can be flexibly adjusted based on geometric conditions and traffic flow characteristics at different intersections.

The reverse variable left-turn lane is a typical example of urban traffic management transitioning from "extensive expansion" to "refined optimization." Its core value lies in achieving maximum benefits with minimal investment through deep integration of time-space resources, providing replicable and scalable solutions for alleviating urban traffic congestion. In the future, with technological advancements and innovative models, this design will further integrate into intelligent traffic systems, contributing to the creation of more efficient and resilient urban road networks.

Author Profiles: Zhao Yue, Wang Shoukuan, Shandong Jiaotong University Zhixing Traffic Engineering Co., Ltd.

Source: https://www.7its.com/index.php?m=home&c=View&a=index&aid=28787

Translated By: 7ITSNEWS