Canadian National Railroad Practice Exam 2026 - Free Railroad Practice Questions and Study Guide

Key or Key Crude trains carry high-hazard materials, so through High Threat Urban Areas or large population centers, speeds are restricted to reduce the risk and potential consequences of an incident. The 35 mph limit is chosen as a safe balance: it provides enough braking distance and control in densely populated areas, while still allowing reasonable travel times. Slower limits like 25 mph would unnecessarily slow operations without a proportional safety gain, and faster limits like 45 or 55 mph would significantly increase stopping distance and the severity of any derailment or fire in an urban setting. So, the maximum speed through an HTUA or population center over 100,000 is 35 mph.