The use of wide medians and clear zones that do not require median and roadside barriers is the current design practice for new and reconstructed rural highway facilities. Constructing or reconstructing roads with full-width medians and clear zones is much more expensive today compared to when the design standards were developed. Considerable costs can be accrued in additional overhead bridge length, earthwork and ROW in new construction projects, and widening of existing right–of-way and bridge structures in reconstruction projects.

This synthesis study focuses on the use of median barriers and roadside barriers and it identifies: (a) the current design practice and the existing body of knowledge, (b) (b) design conditions where adding extra traffic lanes without widening the ROW is acceptable from the point of view of safety and costs if barriers and guardrails are installed, and (c) future research needs.

One of the practical outcomes of the project is a set of Crash Cost Modification Factors (concept found in the German design guidelines) estimated based on the past research for Indiana and simulation experiments executed with the Roadside Safety Analysis Program. These factors can be used to evaluate the safety benefit produced by a modified cross-section of a rural freeway.

Report Number



Rural freeway, clear zone, roadside barrier, median barrier, road safety

SPR Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version