The following description was taken from NYC DoT: Cross Over Mirrors for Trucks
Because of the height of large trucks, it can be difficult for truck drivers to see what is happening directly in front of their vehicles. This has contributed to a significant number of pedestrian deaths in New York City. Cross over mirrors, installed in front of the cab of a truck, are a simple way of eliminating a truck driver’s front “blind spot” and allowing the driver to see any person at least three feet tall and passing one foot in front of the vehicle.
Cross over mirrors are already required on school buses. They are relatively inexpensive and manufacturers typically offer them below list price, as well as provide discounts for bulk orders.