Once the line is in, later work can address the slower sections. HS1 (the section of high speed rail from London to the channel tunnel), was probably partially

Once the line is in, later work can address the slower sections. HS1 (the section of high speed rail from London to the channel tunnel), was probably partially built as it was embarrassingoy obvious going from french HSR to the British Victorian era railways. Infill can always come later once the core is there.