What is the required intersection sight distance for a single unit truck wishing to make a left turn onto a major road with a design speed of 50 mph?

The required intersection sight distance for a vehicle making a left turn is influenced by several factors including the vehicle's speed, turning radius, and the perception-reaction time of the driver. For a single unit truck turning left onto a major road with a design speed of 50 mph, the sight distance needs to account not only for the distance required for the turning maneuver but also for the distance necessary to ensure that the driver can perceive any oncoming traffic safely.

Design guidelines often reference a sight distance of approximately 1.5 times the speed of the vehicle in miles per hour, which, in this case, translates to a need for adequate sight distance over a long enough stretch to provide the driver with sufficient time to make a safe maneuver. For a design speed of 50 mph, the calculations and traffic engineering principles lead to a required sight distance that aligns with the choice of 698 feet.

This value considers potential reaction times, the speed of approaching vehicles, and safety margins necessary for larger vehicles like trucks which may take longer to complete a turn compared to smaller vehicles. Therefore, 698 feet is derived from standard engineering practices for left-turn sight distance at the specified speed.