This paper discusses how a two-lane prestressed concrete bridge can be designed and constructed so that it can be widened easily into a three- or fourlane bridge in the future. The methods presented are the strutted box widening method (SBWM), which applies to concrete box girder bridges, and the strutted girder widening method (SGWM), which applies to precast concrete girder bridges. Two design examples are given. The first is a detailed example that demonstrates how the SBWM can be applied to the popular case of a span-by-span precast segmental bridge. The second example shows how the SGWM can be used to double the traffic capacity of an existing bridge. Four “whatif�? studies are included to demonstrate how two elevated median-based expressways and two major long-span crossings could have been designed and constructed using the SBWM to allow for future widening. The paper concludes with a discussion of a proposed precast segmental extradosed bridge that is to be constructed and widened using the SBWM.
