Which types of roadworkers are permitted to work without Form D line 4?

The correct answer focuses on the specific types of roadwork vehicles that can operate without the restrictions imposed by Form D line 4. Work or wire trains, rail grinding track cars, MPMV (Mobile Production Maintenance Vehicle), and Catenary Maintenance Cars are all included because these vehicles often have specialized functions that allow them to perform their tasks safely while minimizing the risks associated with working in an active rail environment.

This exception is justified as these types of equipment can typically carry out their operations along with standard train movements, often having the necessary safety features and protocols in place. Each vehicle type listed is designed for maintaining or enhancing railway performance, justifying their exemption from the usual Form D line 4 requirements that govern other types of track work.

The other options either limit the scope too much or misidentify the categories of equipment. For instance, suggesting that only specific vehicles like MPMV and rail grinding track cars or just Catenary Maintenance Cars are allowed would incorrectly exclude other types of essential maintenance equipment that are fundamental for effective railway operations.