Section 610.31 - Vehicle tests for fuel economy and exhaust emissions(a) The tests described in subpart D, E, or F may be conducted if existing data or other information are insufficient to support claims for a device in any of these areas:(1) Degree of improvement in fuel economy(2) Effect on exhaust emissions(3) Vehicle applicability(b) The Administrator may determine that, in certain cases, tests using engine dynamometers are adequate for determining the effect of a device. Examples of such cases are given below.(1)Long-term effects. In some cases, it may be necessary for the engine to operate for several thousand miles before the effectiveness can be adequately measured. In such cases an engine dynamometer will permit a less expensive and better controlled durability and economy test than one in which a vehicle must be driven on a durability route and then tested on a chassis dynamometer or test track.(2)Durability requirements. Aspects of engine durability can be efficiently determined using specialized engine testing rather than through durability mileage accumulation in a vehicle. A number of standard engine tests are presently used which can be incorporated into this requirement.(c) When in the judgment of the Administrator a device cannot satisfactorily be evaluated using either dynamometer or track versions of the City Fuel Economy Test and the Highway Fuel Economy Test, the Administrator will select or design other procedures.