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.