This sign means:

The correct interpretation of the sign indicating "No truck over 6.5 metres in length in this lane" reflects the regulations intended to manage the flow of traffic and maintain road safety. Such signs are designed to inform drivers, particularly those of larger vehicles, about restrictions that enhance safety and efficiency on the roadway.

This specific restriction on vehicle length is commonly enforced to prevent longer trucks from using certain lanes that may not be designed to accommodate larger vehicles effectively. Using these roads may pose risks to other vehicles and could potentially lead to accidents or traffic obstructions, making it crucial for truck drivers to adhere to the specified length limits.

Understanding the nuances and specificities of road signs is essential for drivers, as it ensures compliance with local traffic laws and promotes safe driving practices. The other options present variations on restrictions related to height, routing, or broad prohibitions, which do not accurately represent the specific length restriction indicated by the sign in question.