Roadside obstacles are often too close to the roadway to permit the installation of common guardrail designs. Guardrail systems are often modified with a combination of tighter post spacing, nesting of rails, and other guardrail stiffening mechanisms to reduce deflections. NCHRP Research Report 1100: MASH TL-3 Deflection Reduction for 31-Inch Guardrail: A Guide , from TRB’s National Cooperative Highway Research Program, presents a guide on the use of stiffening mechanisms to reduce the deflection for 31-…