...no reliable harness...will protect a dog in a collision or even sudden braking...
.
Military-certified Dog Handler here.
We also worked SearchAndRescue and SearchAndRecovery.
.
Agreed.
Strapped in a harness during a wreck, animals tend toward broken ribs and neck injuries.
Although they may not impact the windshield or get 'thrown free', those injuries will probably degrade their remaining years.
.
Our companions are in our care, dependent on us for food and security.
Our companions would rather be with us than temporarily abandoned in a stand-still house for those hours we work or shop.
Our duty is ensuring their time with us is a joy.
.
Watch dogs playing and climbing trees.
They automatically land with their legs acting as a spring.
Same in a wreck.
.
In a sedan or van, reward them for following your command "Backseat!".
.
.
Turbo, one of the massive Rhodesian Ridgebacks I trained, accompanied me while clearing a closed business during a potential apprehension.
After the scruff (aka 'monkey', 'punk', 'waste of skin') was cuffed and secure with my partners, I gave Turbo the command "Backseat!".
.
She ran outside, around the corner, jumped in the open passenger window, climbed through the pass-through, and laid in the back seat.
Extra treats for that good girl!