In article , Jon Crowcroft
writes
I thouht the points were a big limiting factor between
Hitchin and Cambridge and at Hitchin too...but I am not
a Jarvis employee of course:-)

For a non-stop class 365 EMU, the bottlenecks are as follows:

King's Cross approaches start at 15mph and ramp up to 100mph by, IIRC,
Finsbury Park (my sources for this are a bit out of date).
Limit is then never below 100mph to Hitchin.

Hitchin junction is 40mph for 34c (just under 700m) northbound, 26c
(just over 500m) southbound. Southbound trains are also limited to 75mph
through Hitchin and for about 600m south, then IIRC 70mph over the
connection to the fast line.

Limit is then 80mph to Royston (but this may be out of date).
North of Royston my sources predate the major works of a few years ago,
but show limits varying between 50 and 90mph; the major restrictions are
at the north end of Royston and at Shepreth.

Shepreth Branch Junction (on to the Liverpool Street line) is 30mph.
Then 90mph to Long Road, then 80mph northbound, 90mph southbound, to
Hills Road, then 35mph into the station.

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