Cost of traffic. $1700 a year in US, $2500 in France but huge regional variations (LA = 6000). Add in cost of carbon dioxide emissions....$200 B a year.
In THE ASCENT OF MONEY, Niall Ferguson traces the evolution of money and demonstrates that financial history is the essential back-story behind all history.
From the Brookings Institute an American think-tank. This is another interactive resource that demonstrates the indicators that any central bank official might track to make monetary policy.