There was a canadian show that did something on dog seat belts. they ended up testing them. I should watch the show one day - from my understanding only one car seat belts passed their test (great advertising for them as many people now go out and buy them!).
I will see if I can find somethign about the show, if I remember correction this is the one that passed: Sleepypod Clickit Utility| Top performing Dog Harness | Dog Safety - Sleepypod® | The safest pet company | Dog Carrier | Cat Carrier | Dog Harness
Aha this is the show: Dog harness crash test results - Marketplace - CBC News