Yes, lead poisoning could really be a cause of violent crime

[happyslug]

82. But most Americans did NOT use cars till bout 1954

And most of that increase was post WWII. In urban areas most people walked or took the Streetcar till after WWII. Rural areas embraced the car in the 1920s, but that is AFTER more Americans lived in Urban areas then in Rural Areas. My point is the point if importance is the massive adoption of Automobiles in the Post WWII era and with that massive adoption the vast increase in lead in the atmosphere starting about 1946.

Please note, Automobile use actually increased in the 1930s but that also so how few cars were in use compared to today.

Today the US has 765 Motor vehicles per 1000 people.

http://www.nationmaster.com/graph/tra_mot_veh-transportation-motor-vehicles

Through the US is only the fifth highest per 1000 people, if we restrict the numbers to cars:
http://www.theatlantic.com/international/archive/2012/08/its-official-western-europeans-have-more-cars-per-person-than-americans/261108/

There is some confusion over the numbers, the Author of the second report claims his use of cars includes "cars, pickup trucks, SUVs, and minibuses" but NOT commercial trucks. The problem is almost every state do NOT separate vehicles that way, most have "Cars", "Station Wagons" and "Trucks". In my home state of Pennsylvania a 3/4 ton Suburban is a "Station Wagon", while Subaru outback (1/3 of the size of the Suburban) as a "Truck" just like any other Truck, including 10-20 ton Dump Trucks. Thus I suspect his numbers include "Car" and "Station wagons" including SUVs and Mini-Vans, but NOT Pickups or anything with an open bed, no matter how small or how they are used. Please note my state also classifies truck by hauling capacity, but it starts at 1, for something like the Subaru, 2 for something like a Dodge Dakota, 3 for 1/2 ton trucks, 4 for 3/4 ton trucks etc. If he used that standard, then what was his cut off? If it was at 2 or above, he would have missed almost all of the pickups that people use as personal cars.

Also note, the HUMMER was so heavy, it was classified as a One Ton Truck and thus treated as if it was a Commercial bus by the Federal Government. The Federal Government uses weight alone it is determination (Thus the treatment of the Hummer) but then do you call a 1/2 ton truck a commercial truck if it is a "Pickup"? I suspect the author is using state data for the Federal Government is only concerned about new vehicles (and then for safety and pollution control reasons only). Given he is using only state numbers, he missed almost all pickups and given a lot of pickups are on the road and used for personal transportation his numbers are low.

Here is the number of Motor Vehicles per 1000 people in the US in various years since 1900, the US only broke 1 for 1000 Americans about 1906, within four years you had a 500% increase (1906-1910), in another 10 years (1910-1920) you saw a 160% increase (Small base getting larger, typical of a new product). Then the increase goes to 300% increase between 1920 and 1930, then a barely increased during the Great Depression, deceased during WWII to just above the level of ownership in 1930, then just a 68% increase from 1945 to 1950, then a 78% increase in the 1950s, 75% increase in the 1960s (At the end of which Air Pollution laws kicked in and reductions in lead became the rule).

By 1970 we had over one Motor Vehicle for every two people, given that a typical household includes a Husband, a Wife and three children (we are talking 1960s) then you had a car for almost every adult by 1970. This also show that in 1970, which is the almost the end of leaded gas in the US, you had seen a 185% increase in the number of motor vehicles since 1945, 209% since 1930 and 633% increase since 1920 (and over a 54500% increase since 1905). This massive increase in the number of cars from the 1920s onward lead to a subsequent increase in the use of gasoline, and prior to 1974 that was unleaded gasoline.

1900 0.11
1905 0.94
1910 5.07
1920 86.78
1930 217.34
1940 245.63
1945 221.80
1950 323.71
1960 410.37
1970 545.35
1980 710.71
2000 800.30
2007 843.57
2009 828.04
http://en.wikipedia.org/wiki/Motor_vehicle#United_States