As a result, the transportation sector is becoming increasingly linked to environmental problems. Transport activities contribute among other anthropogenic and natural causes, directly, indirectly and cumulatively to environmental problems.
In some cases, they may be a dominant factor, while in others their role is marginal and difficult to establish. These impacts, like all environmental impacts, can fall within three categories:
i. Direct Impacts:
The immediate consequence of transport activities on the environment where the cause and effect relationship is generally clear and well understood.
ii. Indirect Impacts:
The secondary (or tertiary) effects of transport activities on environmental systems. They are often of higher consequence than direct impacts, but the involved relationships are often misunderstood and difficult to establish.
iii. Cumulative Impacts:
The additive, multiplicative or synergetic consequences of transport activities. They take into account of the varied effects of direct and indirect impacts on an ecosystem, which are often unpredicted.
Transport generates a number of adverse environmental effects from both transport infrastructure and vehicles. Transport infrastructure and the operation of vehicles can affect rural and community character and can sever communities.
Discharges and road crashes have a significant impact on health, and the form of the transport system can be a deterrent to exercise by walking and cycling. The development of car-dependent environments imposes higher average living costs on families and can also restrict mobility for the elderly, children, the poor, the disabled and those who do not wish to own a motor vehicle.