I've been using this one in my tiny subcompact for about 9 months: Clickit Sport - Sleepypod® | The safest pet company | Dog Carrier | Cat Carrier | Dog Harness. It restricts movement ALOT but I think it's pretty widely regarded as one of the safer ones. It is pretty expensive, ~$80. It honestly had a very steep learning curve for my dog and I. He liked to move around in the back seat a lot. With this harness on he can lie down in the seat and sit up and look out the window (tiny car though). He can't turn around or he gets tangled.
The tangling was a big issue. It took a while for him to learn he could only sit up and down in one position. I had to pull over on the road and untangle him many times. He whined about having to be in the harness a lot. We've gotten to a point now where he's comfortable in it and can fall asleep now.
Also, depending on the size of your dog and the length of your car's seatbelt it's possible the seatbelt might not be long enough to loop through the harness. I think my dog is somewhere near the limit of having a long enough seatbelt to loop through the harness effectively. I bought one of these https://www.seatbeltextenderpros.com/ for ~$30 but I haven't been using it lately.
If you want something actually crash tested, I recommend the following three:
- Clickit Sport by Sleepypod (as linked above)
- Enhanced Strength Tru-Fit Harness by Kurgo
- Load Up Harness by Ruffwear
Out of the three, the Clickit is by far the safest, but it does restrict movement the most. However, you want restricted movement as it reduces chances of injury. You don't want harnesses that merely click into the seat belt buckle because they won't have the appropriate anchoring strength or reduction in movement to prevent the dog being ejected from the harness or your vehicle. Majority of damage done is from too much thrashing around or sudden movement during a crash.
277 Heavy duty commercial stitching and stainless steel hardware.
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Look and feel like high quality leather
Soft from brand new, no break in period
Stainless steel hardware
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Will not need maintenance, oiling, waxing or protection from any weather, EVER!
Will not attract water, mud, dirt or grit, can be used in any weather.
Super strong, approx. 40% stronger than any leather.
Light enough to use on any dog, strong enough for any dog too.
I've used Rough Rider Roadie for years. Over 20. They hold up well, they seem to function well. I don't know if these are still available. The seatbelt slips through the harness, the buckles are for sizing and do not affect the strength of the harness - the harness webbing does that. The easy way to put them on is to disregard the directions....