Take Interstate 65 south across the Ohio River and you might not notice you've just spent $4. No toll booth stands between the Indiana border and Louisville. Motorists who frequently travel the route likely have a transponder device, with the cost charged automatically to their account. For those without a transponder, a camera captures a license plate photo and the tolling system operator, with access to motor vehicle records, sends a bill to the vehicle's registered owner. As technological advances make highway and bridge tolling easier and more efficient, technology also is delivering more fuel-efficient cars and trucks. The gasoline-tax...