Upgrading infrastructure often increases the barrier effect. If existing infrastructure is not already built with mitigation measures, construction works provide an excellent opportunity to incorporate new measures. Establishing passages across existing barriers is generally much more expensive than building passages across new roads and railways. Environmental studies that were originally made may be outdated and a new evaluation is often necessary: the fragmentation brought about by the infrastructure could have already affected the area and other sources of fragmentation, unforeseen at the time of the study, could have appeared. Usually upgrading existing infrastructure requires the preparation of an EIA similar to the process described in Sections 5.3.1- 5.3.4.

As before, this enables:

• Analysis and ranking of priorities by superimposing the infrastructure to be upgraded on maps of natural features and of the existing fragmentation.
• Identification of areas of conflict between natural features and the route.
• Discussion about the possible effects of the route. The sensitivity of the habitats with respect to fragmentation, the mobility of the animals, the size of their home ranges and how sensitive they are to disturbance, are all factors to be considered.
• The possibilities of increased traffic density and higher vehicle speed, as a result of a road upgrade must also be taken into account.

The endpoint of this analysis is to describe possibilities for limiting the fragmentation caused by the widened infrastructure or to consider alternatives, taking into account the following:

• Old highly curved roads may be difficult to widen and to adapt to the desired quality and modern standards of traffic safety.
• Broader barriers are more difficult to cross with underpasses, which may be longer and darker and require larger constructions.
• In some cases, building new infrastructure adapted to the landscape with bridges and ecoducts may be more environmentally friendly than mitigating old infrastructure barriers, which were placed without any consideration to landscape or habitats.