A method for determining a trailer length of a trailer attached to a tow vehicle while the tow vehicle follows a path, the tow vehicle having one or more sensors (132, 134) positioned on a back portion of the tow vehicle facing the trailer, the method comprising: transmitting, from a data processing hardware to a user interface in communication with the data processing hardware, a command instructing the user interface to display a representation of a manual mode, a representation of a semi-manual mode, and a representation of an autonomous mode; and receiving, at the data processing hardware from the user interface, a selection of one of the representations (144, 144a, 144b, 144c) of the manual mode, the semi-manual mode, and the autonomous mode; receiving, at the data processing hardware in communication with the one or more sensors (132, 134), first sensor data associated with a first position of the tow vehicle along the path; receiving, at the data processing hardware, second sensor data associated with a second position of the tow vehicle along the path, the second position being different from the first position; receiving, at the data processing hardware, third sensor data associated with a third position of the tow vehicle along the path, the third position being different from the first position and the second position; determining, at the data processing hardware, a trailer length based on the first, second, and third sensor data; and transmitting from the data processing hardware to a user interface in communication with the data processing hardware, instructions to display the trailer length, wherein when the selection is the semi-manual mode, before receiving the first sensor data associated with the first position of the tow vehicle: transmitting, from the data processing hardware to the user interface, a command instructing the user interface to display a first maneuver to be taken by a driver of the tow vehicle to move the tow vehicle from an initial position to the first position; and receiving, at the data processing hardware, a confirmation from the driver via the user interface, the confirmation indicative of the driver following the first maneuver. transmitting, from a data processing hardware to a user interface in communication with the data processing hardware, a command instructing the user interface to display a representation of a manual mode, a representation of a semi-manual mode, and a representation of an autonomous mode; and receiving, at the data processing hardware from the user interface, a selection of one of the representations (144, 144a, 144b, 144c) of the manual mode, the semi-manual mode, and the autonomous mode; receiving, at the data processing hardware in communication with the one or more sensors (132, 134), first sensor data associated with a first position of the tow vehicle along the path; receiving, at the data processing hardware, second sensor data associated with a second position of the tow vehicle along the path, the second position being different from the first position; receiving, at the data processing hardware, third sensor data associated with a third position of the tow vehicle along the path, the third position being different from the first position and the second position; determining, at the data processing hardware, a trailer length based on the first, second, and third sensor data; and transmitting from the data processing hardware to a user interface in communication with the data processing hardware, instructions to display the trailer length, wherein when the selection is the semi-manual mode, before receiving the first sensor data associated with the first position of the tow vehicle: transmitting, from the data processing hardware to the user interface, a command instructing the user interface to display a first maneuver to be taken by a driver of the tow vehicle to move the tow vehicle from an initial position to the first position; and receiving, at the data processing hardware, a confirmation from the driver via the user interface, the confirmation indicative of the driver following the first maneuver.