Sections 60-6,363 to 60-6,374 shall apply to all diesel-powered motor vehicles operated within this state with the exception of the following:

(1) Emergency vehicles operated by federal, state, and local governmental authorities;

(2) Vehicles which are not required to be registered in accordance with the Motor Vehicle Registration Act;

(3) Vehicles used for research and development which have been approved by the Director of Environment and Energy;

(4) Vehicles being operated while undergoing maintenance;

(5) Vehicles operated under emergency conditions;

(6) Vehicles being operated in the course of training programs which have been approved by the director; and

(7) Other vehicles expressly exempted by the director.