Trauma centers are classified into four levels based on their capabilities. Level I centers can provide total care for all aspects of injury. Level II centers can provide definitive care for all patients. Level III centers can assess, resuscitate, and stabilize patients before transfer. Level IV centers provide stabilization and diagnostic services before transferring patients to higher levels of care. Hospitals that pay for on-call coverage of specialties like neurosurgery recognize the limited availability of experts and the demand for their services.