Together with the Digswell Viaduct some ten miles to the south, the flat junction just north of was a major bottleneck, as northbound trains diverging from the East Coast Main Line towards Letchworth and thence to Cambridge had to cross one northbound line and two southbound lines to access the Cambridge Line. Proposals as part of the original electrification work in the early 1970s envisaged a new underpass here and land was set aside for its construction. However, budgetary constraints forced this part of the programme to be abandoned. The land stood empty for many years, but has since been used to provide new housing. A new plan and subsequent application for an order to build a flyover was approved after a Planning Inspectorate report and public inquiry between 11 and 25 May 2010. Construction was completed in June 2013. Original plans were to build the embankment using aggregate trucked in from elsewhere, but eventually it was decided to build up the embankment using chalk taken from the nearby Wilbury Hills, low-lying chalk hills forming part of the Chiltern Hills, from less than away, removing the need for lorry movements along public roads. The chalk was quarried from just beyond the ancient Icknield Way, which at this point is a public bridlepath between Ickleford and Letchworth Garden City, and the contractor was required to refill and replant the quarry afterwards. Since the embankment materials were locally sourced it also meant that the new embankment was effectively pre-seeded with poppies. This means the entire embankment is covered in red poppies during their flowering season giving the name to the location 'Poppy Bank'.
Present day
The scheme has created a new single-track line that diverges from the northbound slow line at Hitchin North Junction just beyond Hitchin station, using a short embankment section of the former Bedford to Hitchin Line, a section of which was cleared of vegetation and made progressively higher, to form a short ramp. The track is carried over the East Coast Main Line on a newly constructed viaduct and onto a new embankment to join the present Cambridge Line at the newly created Hitchin East Junction, closer to. Although this routing skirts around the flat junction in a curve that takes trains over a physically longer distance, it removes the need for them to dwell at Hitchin - sometimes for several minutes - awaiting a path across the tracks of the main London-Peterborough route, thus decreasing the overall journey time to Cambridge in many instances. The scheme improves the punctuality and reliability of both the London-Cambridge and London-Peterborough routes, the latter because Peterborough-bound stopping trains are no longer delayed if running closely behind a Cambridge service being held at Hitchin waiting to cross the flat junction. The flat junction remains in use, providing an alternative route from either the Down Fast or Down Slow line to the Cambridge line. On 26 June 2013, passenger services began to use the flyover, with up to three services per day using it during regular service and driver training. The flyover came into full use in December 2013 with the introduction of the new timetable. The route was designed so that all trains, even heavy freight, can use the flyover. Trains to Letchworth and Cambridge are timetabled to take one minute longer than in the reverse direction. For example, trains from King's Cross to Cambridge which used to leave at XX.15 now leave at XX.14. By January 2015 the only form of traction not to have used the flyover was electric locomotives ; the Union of South Africa became the first steam engine on the flyover when it moved empty coaching stock to Cambridge in preparation for a tour to York.
