Road construction has several impacts on nature and the ecosystem, such as habitat fragmentation or alteration, which is a drastic change in the place that species live. It also impacts the relationship between the species from that place, and their relationship with the environment itself. This can mean that they won't have food or a safe place, or maybe they won't have a predator anymore and the species wihout a predator will spread too much, causing an imbalance in the entire ecosystem. If you build a road in the middle of a forest, this land will be divided in two, and this will cause deep impacts. A road construction also usually brings with it the pollution, from the construction of the road and also from the vehicles that will be using it. But there are mitigation actions that can be taken to help reduce those negative impacts.