Transport infrastructure has both primary and secondary effects on nature. It is possible to distinguish between five major categories of primary ecological effects that negatively affect biodiversity plus a group of secondary ecological effects: (see Section 3.4)

Primary ecological effects

1. Loss of wildlife habitat.
2. Barrier effects.
3. Fauna casualties - collisions between transport and wildlife.
4. Disturbance and pollution.
5. Ecological function of verges (edges of
   infrastructure development).

In practice, these effects usually interact and may significantly increase their negative impact through synergistic effects. The consequences of loss and deterioration of wildlife habitat, barrier effects, isolation, and disturbance can be summarised by the term fragmentation.