In roadway design, what does the formula L = W * S^2 / 60 pertain to?

The formula L = W * S^2 / 60 is used in roadway design to calculate the length of a merging taper, specifically designed for speeds at 40 mph or less. In this context, 'L' represents the length of the taper, 'W' is the width of the lane or the offset required for the taper, and 'S' stands for the speed in miles per hour.

This formula is critical for ensuring that vehicles can safely transition from the new roadway alignment to the existing roadway alignment, particularly in situations where a lane is either added or deleted. When designing for lower speeds (40 mph or less), it is essential to provide adequate taper length to accommodate the lower maneuvering speeds of vehicles, reducing the risk of accidents and ensuring smoother traffic flow.

Using the formula for speeds higher than 40 mph would generally result in longer taper lengths than necessary, which could be impractical for the roadway environment and may not account for the dynamics involved at lower speeds. Thus, the application of this formula specifically to merging tapers for speeds of 40 mph or less highlights its importance in promoting safety and functionality in roadway design.