Travel-Time and Delay Studies

Travel time and delay are two of the principle measures of highway system performance used by traffic engineers, planners, and analysts. Vehicle speed is directly related to travel time and delay and is also used to evaluate traffic and highway systems. There are two types of average speed: time-mean speed (or mean spot speed) and space-mean speed (or mean travel speed). Measuring time-mean speed is described in Chapter 3. The measurement of space-mean speed is discussed in this chapter. Travel time varies inversely with travel speed. A travel-time study provides data on the amount of time it takes to transverse a section of street or highway. These data, combined with the length of the section under study, produce a mean travel speed. Travel-time and delay studies are conducted when the sources and amounts of delay occurring within the section are also noted. This chapter treats the measurement of delay along a roadway segment.