Energy in a Can

Today, my cabby was full of vim and vigor. He was talking a mile a minute and driving like we were in the Grand Prix. Then I realized that he had been guzzling can after can of "Birdie" brand coffee the entire time I was in the taxi. I understand that it takes a fair amount of energy to drive strangers around the busy city of Bangkok, but considering how much caffeine the taxi driver consumed, he could have jumped out and pushed the car the whole way.