The question assumes a dog travelling unrestrained, and that assumption is the first thing to check — and change. An unrestrained dog in a sudden stop becomes a projectile that injures itself and everyone it hits, a dog loose by the pedals can cause the stop in the first place, and none of that depends on trip length. Restraint is where safety starts: many hire and taxi operators require dogs to be secured in their terms, and many jurisdictions require it by law, with the detail varying by place and provider. So the checks below assume you bring the restraint your dog already knows — a crash-worthy harness clipped as designed, or a secured carrier for a small dog — and treat everything else as harm reduction around that fixed point.
Confirm the operator's rules before booking
Ask before you book, not at the kerb with the meter running: does the operator carry dogs, must the dog be restrained or crated, is there a size or breed condition, a cleaning fee, or a rule about which seats a dog may use? Hire companies add their terms about animals in the vehicle and returning it clean and undamaged; taxi drivers may be entitled to refuse an animal they were not told about. Get the agreement in the booking notes where you can, carry a blanket or cover to protect seats you do not own, and confirm the return or drop-off arrangements suit a dog — a hire office with a no-dogs waiting room changes where your dog waits during paperwork.
Doors, windows and the driver's space
Walk the car before the dog gets in. Check the rear doors open and close, and set the child locks so a paw or a shifting bodyweight against a handle cannot open a door from inside; confirm the locks engage rather than trusting the symbol. Check the windows: they should be closed, locked out from rear controls, or opened a crack a head cannot fit through — never enough for a dog to jump or be thrown from, and never rely on a dog 'not being the jumping type' in a strange, exciting car.
Lay a non-slip mat where the dog will travel, because hire-car upholstery and braking slide an unsecured-feeling dog around even inside a harness, and a dog that feels its footing go will scramble, which is its hazard. Then fix the boundary that matters most: the dog stays out of the driver's space — no front footwell, no lap, no head between the seats courting attention. In a taxi, agree the dog's place with the driver before moving off; in a hire car, set the barrier, crate position or harness anchor so the boundary is physical, not a hope you will repeat at every junction.
Ventilation, supervision and the journey's edges
Check ventilation before setting off: air vents or a safe window arrangement that keeps air moving without creating an escape gap, remembering a stationary car heats on mild days. The rule is absolute: a dog is never left in the vehicle — not for the hire-office queue, not for a two-minute shop, not with a window cracked as a substitute for supervision. If a stop requires you to leave the car, the dog comes with you on a lead, or another adult stays with it.
Plan the loading and unloading moments, since more dogs escape at journey's edges than mid-route: lead on before any door opens, doors opened one at a time, the dog settled and restrained before the engine starts and released only after it stops. Keep the trip boring — a toilet break and a chance to settle, water offered at stops on longer hires, and familiar bedding carrying smells into a car.
Even a careful loading routine meets its bad day eventually, and a dog loose in a strange neighbourhood is disoriented as well as lost. That is the gap an alert fills: Lost Pet Alert System messages through KinsLe reach owners in the surrounding area quickly, and a person who catches the dog can contact its owner by direct message from the alert.