Farrington, Nicole

The practices in this guide provide an overview of the current general state of the practice in Minnesota relating to the design, and operation of pedestrian- and bicycle-related factilites.

The practices and policies in this guide are consistent with guidance prepared by FHWA, AASHTO and NCHRP and is primarily intended to apply to new construction, except as noted. These practices and policies provide an overview of the current state of practice in Minnesota relating to the design, operation and maintenance of road systems.

The guidance in MnDOT's Road Design Manual relative to the design of turn lanes is at least 35 years old and is reflective of a time when vehicle speed and volume were lower than they are today. In response to these current conditions, some designers have been providing longer turn lanes. However, this approach has resulted in inconsistent designs across MnDOT's system. In response to concerns about the dated guidance in the Road Design Manual, the inconsistent treatment across the system and the lack of a documented design process; MnDOT developed and documented a new turn lane design process. The suggested design process is based on the notion that turn lanes should be designed to be long enough to accommodate deceleration from the prevailing highway speeds plus the storage needed for left or right turning vehicles. The new guidance provides a check list for designers that have links to look up tables for deceleration based on speed, storage based on volume of turning vehicles and type of intersection control and adjustments for grades and the fraction of heavy vehicles. These guidelines provide a resource for designers that will allow greater consistency between the length of turn lanes and traffic and roadway characteristics.