You'll watch when and where you drive under a pay-by-the-mile plan. By Joan Goldwasser, Senior Reporter December 31, 2007 Carpool moms, exurban commuters and Sunday drivers, take note: You may soon pay more to drive, especially during rush hour. And a fuel-efficient car won't necessarily help.Several states are testing high-tech alternatives to the gas tax you pay at the pump. These new systems, enabled by global-positioning technology, are based on the number of miles you drive and when you drive them. In Portland, Ore., where a pilot program just ended, you might pay as much as nine times the current tax rate if you drive during rush hour. The idea is to make sure that motorists -- even those whose gas consumption wanes -- bear the cost of wear and tear on the nation's roads. A huge national study run by the University of Iowa is ramping up in six metro areas. Thousands of drivers will continue to pay gas taxes at the pump, but they'll also get a simulated bill every month showing how much they would pay under a mileage-based system. At first, the bill will reflect only the amount due, based on miles driven. After a while, drivers will get more-detailed bills documenting their whereabouts. Privacy concerns will doubtless make for battles royal as state legislatures try to balance the need to know with the need for tax revenues. SHARE YOUR THOUGHTS Please scroll down to our Comments Box.