Research | 2013
Florida Department of Transportation Research Project
- Published by: TWO 977-19
Florida Department of Transportation Research Project BDK 84: TWO 977-19: Landscaping of Highway Medians at Intersections, (in progress)
For many years, the Florida Department of Transportation (FDOT) has limited the landscaping
of highway medians at or near intersections. These limitations, detailed in Index 546 of the
Department’s Design Standards, specify the Department’s interpretation of AASHTO Greenbook policy that, “The driver of a vehicle approaching an intersection should have an unobstructed view of the entire intersection . Specified areas along intersection approach legs and across their corners should be clear of obstructions that might block a driver’s view of potentially conflicting vehicles.” These standards, especially those for median trees near intersections as shown on Sheet 1 of 6 of
Index 546, were based on graphical analysis and physics.
As FDOT strives toward more context sensitive designs, some Districts have indicated the need for the consideration of median width, tree size, tree setback, tree spacing, number of trees, or signalization of intersections. In the past, landscaping in the median areas adjacent to left turn lanes was limited to ground cover, regardless of whether or not the area was within the limit of clear sight, and regardless of the length of the turn lane. To incorporate the context sensitive solutions (CSS) approach, FDOT Standard Index 546 was revised in 2010 to allow some flexibility regarding the installation of trees in the median adjacent to left turn lanes. However, these revisions do not change the requirements to provide intersection sight distance or to maintain a clear sight window. These recent efforts for context sensitivity, as well as advancement in technology, suggest a need for an empirical study.
This study is evaluating: (1) whether the standard criteria in the current FDOT Index 546 remain valid for allowing the installation of trees in the median adjacent to left turn lanes, and (2) if enhancement or modification of the current standard criteria is needed, what changes need to be made to the current Index 546 median landscaping criteria with regard to intersection safety and operation. The study includes a national review of state transportation agency standards for intersection sight distance and state policies relative to landscaping at intersections