A quick calculation shows that USPS spends 9.3% of its revenue on drivers alone based upon 2009 operating revenue of 68 billion USD.
That is a lot of money on drivers, and excludes other staff of which there are 623,000+ in total. Total compensation and benefits to workers was 53 billion USD!
Thats one heck of an organisation, and unlike our industry staff costs are obviously the biggest cost centre.