For the first three months of 2008, highway travel has declined by 2.3% nationwide and 5.6% in Idaho, relative to the same three months in 2007. That's according to a 'Traffic Volume Trends' report put out by the Federal Highway Administration.
Travel on all roads and streets dropped by 4.3% for March '08 compared to March of the previous year. Travel for the month is an estimated 246 billion miles. In Washington, people drove 781 million vehicle miles in March. Across the border in Idaho, it was 418 million. That's a drop of 6.2% in Washington and 6.3% in Idaho.
The report doesn't address why the drop in driving but I know I've been riding the bus much more frequently due to gas prices.