1. In 1931, with some cars with single tail lights & no seat belts,
there were 31,963 deaths caused by vehicle accidents.
25. 8 deaths per 100,000 people,
when the U. S. population was only 124,039,648.
2. In 2012, with far more LED lights & far more seat belts,
there were only 33,56 deaths caused by vehicle accidents.
10. 69 deaths per 100,000 people,
when the U. S. population was 313,941,000, almost tripled.
Those statistics don't include the total number of motor vehicle accidents, nor the number of accidents directly attributable to taillights and brake lights, or lack thereof; i.e., rear end collisions,
and most importantly, your argument using those statistics doesn't mention the difference in the overall construction of vehicles in 1931 compared to modern vehicles.
The recent unfortunate accident involving a Ford Barn member in Texas had nothing at all to do with taillights and brake lights, although seat belts most likely played a part in reducing the severity of injuries.
With the exception of the WWII years, when speed limits and driving in general were arbitrarily reduced for rubber conservation, the death rate from motor vehicle accidents in the US didn't begin a significant and consistent decline until the 1980s.
Dual taillights, brake lights and turn signals became a Federal requirement in 1958. Up to that point, many cars, and commercial vehicles, still only had one taillight and brake light.
Passenger restraints became a Federal requirement in 1968. Air bags, in 1998.
Center high-mount brake lights became a Federal requirement in 1986 for cars, and 1990 for light trucks.
None of those items--taillights, brake lights, passenger restraints, air bags, center high-mount brake lights--are retroactive requirements, meaning there are still many cars on the road without some or all of them, although the percentage of such cars driven on the road on a daily basis has declined significantly, and will continue to decline.
Furthermore, the 1974-1988 arbitrary reduction in the National maximum speed limit to 55 MPH had virtually no effect on the motor vehicle death rate. In fact, in some of those years, the death rate actually increased.
The purpose in mentioning the items above is not to argue the brake light taillight issue; it's simply to point out that there's a lot more to the motor vehicle death statistics than just taillights, brake lights and seat belts.
If you want to make a valid argument for multiple taillights, brake lights and center high-mount brake lights, you should use statistics for motor vehicle accidents involving rear end collisions, not the death rate from all motor vehicle accidents.