ABSTRACT
Traffic is the movement that occurs in a particular transport mode (Section 30.1). This
book deals solely with the traffic due to road transport. Traffic flow measures the rate at
which movement occurs and therefore indicates the use that road transport is making of a
piece of road. In some places the term traffic volume is used instead of traffic flow. This
book uses flow rather than volume, as volume refers to a quantity rather than a rate.
Indeed, flow rate would be a more precise term than the conventional flow. Traffic
capacity is the maximum possible traffic flow on that road. The difference between flow
and capacity is discussed further in Section 17.4.4. Although flow and capacity are thus
dominant numerical indicators of traffic, it must be emphasised that they are not the only
criteria for assessing road usage. Safety (Chapter 28), economics (Section 33.5),
environmental impact (Chapter 32) and aesthetics (Chapter 6) are other major factors that
must be considered.
