Treat a stationary car as a heating problem first
A moving car with air conditioning is manageable in heat; a stationary car in a jam is not, because airflow stops and sun through glass heats the cabin fast, even with windows cracked. Your first decisions in a jam are thermal, not behavioural. Keep the engine and air conditioning running if traffic is truly stopped and it is safe to do so, aim vents toward the back where your dog rides, and shade the window on her side with a sunshade, a light towel, or clothing hung there.
Water, wetting, and what actually helps
Offer small drinks of cool — not ice-cold — water every few minutes rather than one huge bowl she gulps and vomits back. If panting is building, wet her coat through to the skin with tepid water, especially the belly, armpits, and paws, and fan the damp coat or position her in the air conditioner's stream; evaporation is doing the cooling, so a misted topcoat on a thick double coat achieves little. A damp light towel draped over her can help a short-coated dog, but remove it if it dries and starts trapping heat. Skip ice packs against the skin and icy water, which can constrict surface blood vessels and slow the cooling you want. The aim is steady, gradual temperature reduction while you watch her response minute by minute.
Settling a hot dog is mostly about stillness
An anxious dog in a jam paces, whines, and tries to climb forward — all of which generate more heat. Lower the stimulation instead of entertaining her: close the shade on the busy side, speak quietly, and give her something calm and stationary to do, like licking a small amount of wet food smeared on a mat, which occupies without exertion. Toilet needs add to restlessness, so if the hard shoulder or a verge can be reached safely and legally, a brief lead exit for a toilet break and a moment of cooler outside air can reset her — but keep it short, keep her off scorching tarmac, which burns pads quickly, and never walk her along a live carriageway. Never leave her alone in the car while you go for help or supplies. In heat like this, that decision, not the jam, is the one that kills dogs.
Learn the line between hot and in trouble
Heavy panting on a hot day is expected; panting that does not ease when cooling starts, thick drooling, bright red or muddy-looking gums, glassy eyes, vomiting, diarrhoea, wobbliness, or a dog who becomes unusually quiet and unresponsive are emergency signs. If you see them, stop gradual measures being your only plan: pour tepid water over her whole body, get air moving across her, and phone the nearest vet while someone else drives the moment traffic allows, or call for help to reach you. Tell the vet her breed and age — flat-faced breeds, elderly dogs, puppies, and overweight dogs tip into heatstroke far sooner — and keep cooling during transport, with wet towels refreshed and windows open. Do not wait to see whether she rallies. Heatstroke worsens after the dog looks briefly better, which is why the vet call belongs at the first danger sign, not the last.
Arrive differently next time
Once home, let her rest somewhere cool, offer water and a normal meal only when she is fully settled, and note how she coped — a dog who struggled badly in one jam deserves a changed plan for the next hot journey: travelling early or late, a route with shaded stopping places, or not travelling on the hottest day at all. If you are unsure whether she is coping, put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library, and a vet stays the call for any danger sign.