Under the Vienna Convention on Road Signs and Signals, what does a blue circular sign generally indicate?

Under the Vienna Convention on Road Signs and Signals, a blue circular sign generally indicates a mandatory instruction.

Mandatory signs tell road users what they must do, such as keeping to a specified direction, using a particular lane, or following a route for a class of traffic. The blue circular format helps distinguish these instructions from prohibitory signs, which are generally circular with a red border, and warning signs, which are generally triangular.

The convention was adopted in Vienna in 1968 to promote greater consistency in road signs and signals across countries. It provides internationally agreed meanings and design principles, but national road authorities may add details, symbols, or local variations.

A blue circle does not always mean the same thing as a blue rectangular information sign. Circular form is important: the shape identifies the sign’s regulatory role, while the symbol inside communicates the particular action required.