The 4.5km extension to the Metropolitan Line is being promoted by Hertfordshire County Council in partnership with London Underground and Network Rail.
Consultant Mouchel is working up designs, which are being developed with the aim of starting construction in Spring 2014.
Under the extension plans, Watford station will be closed, with new stations at Ascot Road and Watford Hospital built in its place. Viaduct and bridge construction work alone is expected to cost more than £10m.
Goverment funding was confirmed last November. The project promoters submitted a Transport and Works Act application to the transport secretary Justine Greening in January, which must be approved before any work can start.
The industry day will be held on 19 April at Watford Football Club, Vicarage Road in the Elton John Suite.
Interested firms can register by e-mailing [email protected] giving company name and details of up to three attendees. Applications need to be submitted by 12.4.2012.
