What form should be filled out for private car passengers when their record is unavailable and eMD is down?

The Onboard Passenger Record is the suitable form to use for private car passengers when their record is unavailable and the electronic Manifest Data (eMD) system is down. This form serves as a temporary solution to ensure that all passenger information is accurately captured during situations where the normal electronic systems are not operational. By using this form, train staff can ensure that they maintain an accurate account of passengers on board, which is crucial for safety, security, and operational purposes.

While the other options might sound relevant, they do not specifically cater to the needs outlined in the question. The Emergency Passenger Log is typically used in crisis situations, the Temporary Passenger Report serves a different function related to operational reporting, and the Manual Boarding Form is often used for the standard boarding process rather than addressing issues with unavailable records. Thus, the Onboard Passenger Record is explicitly designed for situations like the one presented in the question.