scope:

Purpose

The widening of highway bridges has become common. Several factors contribute to this demand for wider bridges:

a. Increased traffic volumes requiring additional lanes;

b. Safety hazards of narrow bridges requiring wider shoulders; and

c. Provision for bikeways and pedestrian ways.

The availability of funds under special programs, such as the Intermodal Surface Transportation Efficiency Act (ISTEA), is enabling public agencies to widen many functionally obsolete bridges as needed to eliminate safety problems. If a bridge was designed for current live loads and has not deteriorated appreciably, widening is likely more cost-effective than complete replacement.

Many problems unique to bridge widening are not encountered in work on new bridges. Failures or serious maintenance problems can be created by misunderstanding these problems. Each bridge widening is unique. This report provides the designer and constructor with general guidelines for bridge widening.

Emphasis is placed on construction practices, but because construction sequence, structure type, framing details, and other decisions critical to the success of the work are determined during the design phase, some discussion of design concepts must be included. Structural analysis and design for bridge widenings is not addressed. Much of the discussion that follows also applies to new bridges constructed in stages, part width at a time.