ABSTRACT
Bridges may need modification to accommodate widened motorways, to
prevent deterioration from the environment, to distribute secondary (traction
and braking) traffic and seismic forces, or strengthened in order to carry an
increased volume and mass of traffic. In some cases, a bridge may have to be
completely replaced. (Strengthening has been dealt with in Chapter 7; this
chapter deals with the other issues.)
The worldwide economic growth that has taken place in the last 20 years
or so has brought with it a concomitant growth in all forms of transportation
(road, rail and air). This increase in mobility generally, and road traffic in
particular, has been notoriously difficult to forecast and the increased traffic
has put existing transport systems under an intolerable strain. Where trunk
roads pass through city centres the problem is very acute, causing long delays
and a build-up of exhaust emissions. The only resort is to provide a by-pass.
However, the environmental impact of new road schemes is generally seen to
be negative, and the obstacles placed in front of relatively straightforward by-
pass schemes can be both frustrating and expensive. The recent construction
of the Newbury by-pass in the UK is a case in point (Cole, 1996).
