The realized transport demand, expressed in passenger or ton-km, is the multiplication of transported volume and the distance it is carried over. It can increase for two reasons:
- The first is a growth in the volumes of passengers or freight being carried. This is an outcome of growth in population, production, consumption, and income, which is illustrative of aggregate demand.
- The second is a growth in the average distance over which passengers or freight are being carried. Outsourcing, offshoring, economic specialization (factors linked with globalization), and suburbanization are all relevant factors behind this trend.
These two factors often occur concomitantly, creating multiplying effects on the transport demand.