Methodology to Evaluate the Effects of Access Control near Freeway Interchange Areas

Access connections and signalized intersections within the functional area of an interchange can adversely impact safety and operations at the interchange crossroad and on the freeway, and can cause the interchange to fail prematurely. Standard practice is to acquire a minimum of $90\mathrm{m}$ $\left(300\mathrm{ft}\right)$ of limited access right-of-way beyond the end of the acceleration/deceleration lanes for rural interchanges and $30\mathrm{m}$ $\left(100\mathrm{ft}\right)$ in urban areas. Although the safety and operational benefits of managing access in freeway interchange influence areas are clear, the cost effectiveness of purchasing access rights at the time of interchange construction has not been established through national or state-level research. The primary objective of this study was to assess the relative costs and benefits of purchasing additional limited access right-of-way at the time of construction in lieu of retrofitting interchange areas after functional failure. The study methodology included the following basic steps: (1) traffic operations analysis of the study interchange with varying configurations of signalized access spacing using CORSIM; (2) safety analysis of a sample of Florida interchanges with varied access spacing; and (3) cost/benefit analysis of acquiring varying amounts of limited access right-of-way. This study indicates that the long-term safety, operation, and fiscal benefits of purchasing additional limited access right-of-way at interchange areas greatly exceed the initial costs. The findings suggest that state transportation agencies and the traveling public may benefit greatly by an increase in the amount of limited access right-of-way at interchange areas to a minimum of $180\mathrm{m}$ $\left(600\mathrm{ft}\right)$ and a desirable $400\mathrm{m}$ $\left(\mathrm{1,320}\mathrm{ft}\right)$ .