Urban passenger and freight transport systems are separate systems sharing similar infrastructure, but impacted differently by density. The common perspective in urban planning is that higher densities are preferable since they generate economies for services and opportunities in the use of public transit. However, high concentration levels generate conflicts between freight and passenger transportation, induce congestion, pollution, noise, higher levels of energy consumption (lower speed and idling), and risks of accidents. This trend is a non-linear one. In a low-density setting, such as in rural or low-density suburban areas, delivery costs per unit are higher due to the same number of deliveries requiring longer distances. In a medium-density suburban setting, delivery costs are lower as shorter delivery distances are experienced while very few constraints are still impacting them. As density increases, however, a set of constraints becomes more prevalent, particularly as it relates to parking. Delivery costs thus increase rapidly.
For retailing, higher densities are related to higher sales per floor space, but also less space available for storage. All this implies more frequent deliveries, which are taking place in an environment where there is limited parking available and competition for the use of road and curb space. This may also incite the usage of smaller delivery vehicles (either by choice or imposed by regulation), which results in more frequent deliveries and higher costs. This is the main reason why freight distribution in higher-density settings commonly requires mitigation strategies.