You must retain the information placed into the Accident register for a period of 3 years for all accidents after April 29, 2003. (49 CFR §309.15(b))

Non-hazmat carriers do not need to report an accident. However, you must maintain an accident register when the accident meets this criteria:
(i) there was a fatality;
(ii) there was bodily injury to a person who, as a result of the injury, immediately received medical treatment away from the scene of the accident; or
(iii) one or more motor vehicles incurred disabling damage as a result of the accident, requiring the motor vehicle to be transported away from the scene by a tow truck or other motor vehicle.

If you transport hazardous materials or hazardous waste, you must report incidents to the U.S. DOT and other agencies when, as a direct result of the hazardous materials:
(i) a person is killed;
(ii) a person receives injuries requiring his or her hospitalization;
(iii) estimated carrier or other property damage exceeds $50,000;
(iv) an evacuation of the general public occurs, lasting one or more hours; or
(v) one or more major transportation arteries or facilities are closed or shut down for one hour or more.
(See �171.15 Immediate notice of certain hazardous materials incidents; and �171.16 Detailed hazardous materials incident reports for more information regarding accident reporting requirements for hazardous materials carriers.)

Yes. It does not matter which vehicle has disabling damage and required to be towed.

An accident is an occurrence involving a commercial motor vehicle operating on a public highway which results in: a fatality, injuries that requires immediate medical treatment away from the scene of the accident; or one or more vehicles incurring disabling damage that requires a vehicle to transported from the scene. (�390.5)