English to French Tech/Engineering Transport / Transportation / Shipping train installation of a railway

Can anyone translate "greenfield versus brownfield" in French? Thank you.

No conservation areas are traversed by the existing railway line and this is therefore not considered to be an area of concern. Should future expansions of the railway infrastructure enter into Greenfields areas, these should be investigated to determine the presence of natural areas. However, it should be noted that large portions of the Madagascar natural wildlife is endemic to the Island and hence have a high conservation status.
The provision of contingency costs is required to provide for unseen conditions encountered during the implementation phase of the project. The percentage allocation of contingency costs against different disciplines are also dependent on the implementation environment (greenfields versus brownfields), level of engineering development (increasing volume accuracy and therefore reducing contingency requirements) and implementation strategy (schedule and contracting formats).