What is the minimum permissible transition length?

The minimum permissible transition length of 100 feet is based on design standards intended to ensure safe and comfortable driving conditions. Transition lengths are used in roadway design to gradually change from one alignment or cross-section to another, such as changing from a straight roadway to a curve. The 100-foot transition provides sufficient distance for drivers to adjust their vehicle speed and positioning in response to changes in road curvature or lane configurations.

This length helps prevent abrupt changes that could catch drivers off guard, thereby reducing the risk of accidents. The standard is established through extensive research and engineering practice, taking into consideration factors such as vehicle dynamics, driver perception, and road safety principles. A transition length of 100 feet strikes an appropriate balance between safety, roadway efficiency, and land use considerations, making it a critical element in highway design.