The section of railway near Hitchin would remove one of the country's bottlenecks, taking the line to Cambridge over the main line route.
Currently trains travelling from London to Cambridge have to cross three other lines to switch between the East Coast Main Line and lines to Cambridge.
Network Rail says the £60 million link would cut delays to train services by almost 18,000 minutes each year and help create the capacity to run more services to and from the capital every hour.
It hopes that permission for the project will be granted by early 2011, enabling work to start later that year. This would mean that trains could start running on the line at the start of 2014.
Network Rail route director Richard Lungmuss said: "The investment we are planning in the Hitchin area will improve transport links, reduce passenger delays and increase the number of services. Rail users will benefit as we remove the biggest remaining pinchpoint on the East Coast Main Line."