What does it mean when the flashing blue light of a vehicle is switched on but not the siren?

When a vehicle displays a flashing blue light without using the siren, it is warning other road users about potential dangers ahead, such as accidents, or signaling that emergency vehicles like the fire brigade are on duty. The use of the blue light alone (without the siren) is specifically for providing a warning, not for demanding that other vehicles make way immediately, which would require both the blue light and the siren. The third option, about a breakdown vehicle, is not correct—breakdown vehicles use a yellow (amber) light, not blue. So your selection of answer 1 and 2 is correct. Remember: blue flashing light without siren always means warning of a hazard or that an emergency service vehicle is on an urgent assignment.