Variables that affect the intensity and scale of police response at the scene include the type of motor vehicle and train involved in the accident and whether the accident has caused a derailment. It is important that the police and railroad dispatchers be notified immediately by the responding officer so that emergency responses can be initiated. The responding officer's first priority must be to care for human life: both those injured in the accident and those who may face imminent or potential hazard as a result of the accident. Bystanders, witnesses, and traffic at the scene must be controlled, and the accident scene should be sealed off to all but emergency personnel. Specialized control measures as well as technical advice and assistance are required in accidents involving hazardous or toxic materials. After the immediate emergency is under control, the officer must gather information which describes and identifies the train and the grade crossing. The train crew can assist the officer in obtaining this information and in identifying damage and potential hazards. Physical evidence should be collected and documented, and photographs of the scene should be taken. Measurements should be made of temporary marks (e.g., body positions, scuff marks), other forms of evidence such as gouges and skid marks, and permanent objects relative to each other. Following these initial procedures, the train may be released, and the followup accident investigation may be initiated. Questions based on materials in the training key are included together with their answers.