The Train operating Companies bid for access. The Track Access Conditions under which the bids are dealt with contain decision criteria which Railtrack uses to allocate scarce capacity. The prediction of noise and vibration from the new lines is an important part of the Environmental Assessment which Railtrack must carry out. If these predictions show even a fairly small increase Railtrack must provide noise insulation of premises or barriers to mitigate noise at source. Barriers can take the form of earth bunds or walls made of wood or other materials.
Vibration is minimised by the use of relevant construction techniques.
The need for noise barriers and the type provided is a matter for the detailed design that is beginning now and is a matter that can also be discussed with local residents. It will be at least 6 months to a year before Railtrack will be in a position to address this issue after all the facts are available. If the line is widened then there will be no space for the footpath anymore, cutting off access Harmer Green Lane and Digswell. The present alignment of the footpath will be taken by the new railway work. This issue will be addressed in the Transport and Works Order application.