Allstate-owned Esurance has begun marketing auto insurance for which consumers essentially pay by the mile. The new product is called “Esurance Pay Per Mile,” coverage enabled by a small telematics device that plugs into the OBD-II of a vehicle dashboard and automatically tracks mileage and GPS locations. How the policy works: there’s a low monthly base cost, with additional charges per mile driven, with a maximum charge of 150 miles in a day.