HS2 Ltd published a review of route alignments for HS2 Phase One in January 2012, in particular reviewing the case for an alignment in the Chiltern Line and M40 corridors and an alignment in the M1 corridor. These were found to cost £3 billion and £2.2 billion more than the consultation route respectively. Neither route could be built to the same design speed as HS2 with both options therefore producing fewer economic benefits than the consultation route. The route for Phase Two is currently the subject of a public consultation. On the eastern leg a significant proportion of the route runs in existing transport corridors (the M42 and the M1). The options report published by HS2 Ltd reviewed a short listed alternative alignment in the M6 corridor rather than the WCML corridor that is the subject of the consultation.