On Sat, 26 Jun 2010 16:15:55 +0100, Basil Jet
wrote:

Why are American cities full of open girdered viaducts whereas British
cities are full of brick viaducts?


Because bricks were easily available, and long girders were not?

US viaducts also post-date the introduction of steel. At the time
most British lines were built, metal girders would have been made of
wrought and cast iron and could not span nearly as far as the later
steel girders could. So brick was the right choice.

Brick viaducts also allowed the arches to be let to produce rental
income. Many of the businesses that were displaced by railway viaduct
construction were relocated to the railway arches.