Most of the principles previously discussed for median transitions (Art. 6.9.3) apply
here as well. Transition designs should gradually stiffen the approach system to avoid
vehicle pocketing, snagging, or penetration. Some considerations of importance follow.
The concepts are appropriate for both new construction and retrofits.
• The splice between the rail of the approach barrier and the bridge rail should develop the tensile strength of the approach rail.
• Strong-post systems, or combination normal-post and strong-beam systems, can be used for transitions. These systems normally should be blocked out to avoid snagging. Also, a rub rail may be desirable with W-beam or tube-type transitions. Tapering the rigid bridge railing end behind the transition members may also be desirable. The rub rail and railing taper are specially appropriate when the approach transition is recessed into the end of a concrete railing or other rigid hazard.
• Use a gradual transition, typically 10 to 12 times the difference in lateral deflection of the two systems. Gradually stiffen by decreasing post spacing, increasing post size, and strengthening the rail (nested W-beams or thrie-beams, for example).
• Eliminate curbs, inlets, and other drainage features in front of the barrier. Keep the slope between the edge of the driving lane and the barrier to 1:10 or less.
• When possible, relocate roads that intersect near the end of the bridge and interfere with a proper transition. Crash cushions may provide an option in some cases.
