Method for partitioning a widening zone of a traffic lane delimited by two edges (202, 203), the method being implemented by a device, the device driving so automated a vehicle, the vehicle being capable of being driven by a driver, along a reference path, said vehicle traveling on said traffic lane, said vehicle comprising lateral positioning assistance relative to the reference path, said process comprising the steps: • detection of an upcoming division of said traffic lane into at least two new lanes (209, 210); • determination of the widening zone of said traffic lane; • determination, in said widening zone, of the reference paths (212, 213) capable of reaching each new path (209, 210); • calculation of a longitudinal distance relative to the start of said widening zone, said longitudinal distance is a function of the reference paths (212, 213) and the edges (202, 203); • determination of a first sub-zone of said widening zone between the start of said widening zone and said longitudinal distance, said first sub-zone being limited transversely by the edges (202 and 203), and determination of a second sub-zone corresponding to the complement of said first sub-zone with respect to the widening zone; the method being characterized in that when the vehicle is in the first sub-zone, the method further comprises a step of selecting a first reference path among the determined reference paths (212, 213), the selection being made from information acquired by at least one sensor of said vehicle, information acquired by at least one sensor of said vehicle is an activated side of the indicator, another vehicle preceding and driving more slowly than said vehicle, a speed of said vehicle less than a setpoint of the vehicle, and/or a lateral position of said vehicle in the widening zone of said traffic lane; when the vehicle is in the second sub-zone, the method further comprises a step of selecting a second reference path among the determined reference paths (212, 213), the selection is made solely from at least one action on the steering wheel by the driver, an action on the steering wheel by the driver is a rotation of the steering wheel and/or a rotation torque applied to the steering wheel. • detection of an upcoming division of said traffic lane into at least two new lanes (209, 210); • determination of the widening zone of said traffic lane; • determination, in said widening zone, of the reference paths (212, 213) capable of reaching each new path (209, 210); • calculation of a longitudinal distance relative to the start of said widening zone, said longitudinal distance is a function of the reference paths (212, 213) and the edges (202, 203); • determination of a first sub-zone of said widening zone between the start of said widening zone and said longitudinal distance, said first sub-zone being limited transversely by the edges (202 and 203), and determination of a second sub-zone corresponding to the complement of said first sub-zone with respect to the widening zone; the method being characterized in that when the vehicle is in the first sub-zone, the method further comprises a step of selecting a first reference path among the determined reference paths (212, 213), the selection being made from information acquired by at least one sensor of said vehicle, information acquired by at least one sensor of said vehicle is an activated side of the indicator, another vehicle preceding and driving more slowly than said vehicle, a speed of said vehicle less than a setpoint of the vehicle, and/or a lateral position of said vehicle in the widening zone of said traffic lane; when the vehicle is in the second sub-zone, the method further comprises a step of selecting a second reference path among the determined reference paths (212, 213), the selection is made solely from at least one action on the steering wheel by the driver, an action on the steering wheel by the driver is a rotation of the steering wheel and/or a rotation torque applied to the steering wheel.