I have no idea on statistics but I would imagine there weren't many people that had cars in 1918.
So I looked it up. According to this article there were 5 million registered vehicles in the US in 1917. There were about 103 million Americans in 1917. So would 5 percent of the population no longer driving be enough to increase life expectancy? I have my doubts on that.
https://www.scientificamerican.com/article/the-motor-vehicle-1917-slide-show/