The street is calm until a siren turns the corner. Your dog startles and barks. A noisy vehicle passing close by is not a fair first lesson in confidence. Move to a safer, quieter place if you can and let your dog recover. Keep the lead secure, but don't drag them toward the sound to prove it cannot hurt them.
Check how they react once the noise has passed. Do they shake off and resume sniffing, or stay tense and scan for the next sound? If they remain distressed, shorten the walk. Some dogs may need a quieter route or time of day for now. New or worsening sound sensitivity warrants a veterinary check, especially when other ordinary sounds also become difficult.
Practice a tiny sound, not a whole siren
On a relaxed day, a low-volume recording of traffic or a siren can be played so softly that your dog notices but stays comfortable. Offer a treat or a favorite quiet activity, then turn the sound off. If they freeze, hide, bark, or refuse food, lower the volume or stop. Increase the intensity only gradually across sessions. Recordings are not identical to real streets, practice outside later with enough distance and a way to leave. For more on coping with loud sounds between outings, see the noise-fear guide, make space from traffic first
Avoid using real emergency vehicles as training equipment or standing near roads to get more repetitions. If your dog panics, tries to escape, or has severe noise fear, ask a qualified, reward-based behavior professional and your veterinarian for a plan. A successful walk may simply avoid the loudest road while your dog learns that you will help them move away.
Sources: Dogs Trust: What to do if your dog is scared of loud noises. Dogs Trust: Sound therapy and firework training.