The spatial organization of transportation and mobility
Common Fallacies in Transport Geography
Access is not accessibility. Many transport systems have universal access since no specific user can have a competitive advantage over others; access is the same for everyone. For instance, a public highway system can, in theory, be accessed by anyone such as a major trucking company having a large fleet, its competitors, or by an individual driving an automobile. Thus, access is uniform wherever one is located in regard to the transport system as long a there is a possibility to enter or to exit the system. On the other hand, accessibility varies according to one’s location within the transport system. Access is thus uniform while accessibility is not; the latter is a relative concept. On the above transport network, locations a, b and c all have access to the system. However, location b appears to be the most accessible two due to its central location in relation to the network.
Distance is not time. Distance often tends to be interchanged with time when measuring the performance of transport systems, which is a conceptual error. While distance remains constant, time can vary due to improvements in transport technology (positive effect), because of congestion (negative effect) or regulations such as speed limits. A simple and common way to express this relationship is speed; the unit of distance traveled per unit of time. Driving one kilometer through Manhattan is not the same as driving one kilometer through an Interstate in Iowa even if in both cases the same unit of distance has been traveled. Distance is thus a uniform attribute of the geography, while time is relative. On the above transport network, while distance is a uniform attribute, each segment has a travel time expressed as speed, which due to capacity and congestion, varies differently from distance.