A method for detecting an exit lane for a motor vehicle includes: detecting, in images acquired by an onboard camera, marking lines on the ground on the right and on the left laterally delimiting the main traffic lane, determining first and second heading angles with respect to the detected marking lines, providing a first, standard exit lane detection state, based on the comparison of the first and second heading angles with a predetermined threshold, and providing a second, coaxial exit lane detection state, based on the comparison between the derivatives with respect to time of the variation of the first and second heading angles and of the verification that the value of the first or the second heading angle remains substantially close to a zero value.