On Mon, 29 Sep 2008 12:55:57 +0100, Robert
wrote:

I think you have misunderstood Malthouse’s remarks about trains’
speeds. He compared Brunel’s approach to civil engineering, which
allowed for speeds in the future to be much higher than those current
in 1833, to that of others active at the time. Malthouse then stated
that “And he was right: trains can run at well over 150 mph today.” In
my reading this sentence does not refer directly to speeds on the GWML.

Brunel designed a level straight route because the available engines
were too underpowered to climb hills at speed and the shortest
distance between two points is a straight line. He was designing the
best route for the trains he had at the time and wasn't considering
what might be running on it 150 years later. The fact that the route
is suitable for modern 1970s high speed trains is just luck and not
design.