Using Benefit/Cost Analysis for Auxiliary Turn Lanes for New Access Connections

• Authored by:  Dr. Vergil G. Stover
• Co-authored by:  Philip B. Demosthenes
• Event:  2015 National Conference Seattle

USING BENEFIT/COST ANALYSIS FOR AUXILIARY TURN LANES FOR NEW ACCESS CONNECTIONS

The benefits to public safety and traffic operation compared to the costs of installing access connection improvements is a frequent topic of discussion and sometimes controversial. This paper discusses the difference between the applications of benefit-cost analysis (BCA) to access connections that are an element of a roadway reconstruction project compared to the BCA for a new access connection to an existing roadway.  Use of a BCA for establishing access design warrants is discussed.  The nature of the potential benefits and costs to road users (public) and to the private entity (developer/property owner) are identified and the allocation of and ability to establish a monetary value for each benefit and cost element evaluated.

Economic analysis is a useful method to identify situations in which turn lanes can be justified economically at an existing intersection taking into account construction and new right-of-way compared to operation and safety benefits. There have been several studies regarding the B/C of left-turn lane installations based on the underlying assumption that the analysis is for public intersections where costs will be paid by public funds and the benefits will accrue to the public in the form of safety and improved operations at an existing intersection; most recently, NCHRP Report 745, 2013.

However, when a new access connection will be to service a new development, the benefits and cost accrued are borne by different parties. There is always a negative benefit to the traveling public when comparing the before and after situation due to additional delay and increased crash risk. The primary benefit accrues to the development. In most jurisdictions, the cost of the new access is borne by the development.