Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets (2020)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

- 12 - 4. Performance Measures This project develops trip-based (or O-D based) travel time measures in addition to the traditional facility- based measures used in the HCM. Performance measures that relate to the trips taken by travelers are considered the best approach, for the following reasons: • Trips relate more directly to the traveler experience – they are how travelers actually experience the system. Facility- and segment-based measures are still useful in this context because they help practitioners identify and treat specific problems, such as bottlenecks. • Each O-D within a freeway and urban street system uses a specific lane or set of lanes. Under congested conditions, each lane across the facility may be operating very differently, and thus evaluating the performance of the O-D would take into account the specific lane usage for those trips. • Measuring performance at the trip level is much more revealing for advanced operations strategies, such as Active Traffic and Demand Management (ATDM) and Integrated Corridor Management (ICM). Many components of these strategies seek to influence demand and to balance demand with available capacity. Understanding what effect strategies have on trips is important for selecting and modifying these strategies. • Moving to trip-based measures is a logical step in the evolution of the HCM. The discipline of performance measurement is moving in the direction of trip-based measures. As additional data become available over the next several years to track the movement of individuals (hand-held devices) and vehicles (connected vehicles, and eventually, automated vehicles), development of trip-based measures from direct measurements will be enabled. Currently, it is possible to derive trip-based measures synthetically, but when direct measurements become available, we expect a rapid increase in the interest for trip-based measures. • Trip-based measures are the basis for measuring accessibility. A logical extension of trip-based measures, which are based on travel between specific origins and destinations, is the measurement of accessibility. Accessibility is defined by two components: 1) the presence of opportunities; and 2) the ease with which those opportunities can be obtained or “reached.” Accessibility can be improved by improving the movement between opportunities or by moving opportunities closer to travelers. Because it considers not only the performance of trips on the system but also how trips interact with the entire built environment, accessibility is a key indicator of the quality of life for a transportation agency’s customers. Figure 3 shows the strategy behind selecting performance measures for the project. Both facility and trip measures are recommended. Trip-based travel time measures are the most direct indicators of the traveler experience but facility-based travel time measures also are useful for analysts to understand since many improvement strategies are facility oriented. Other facility-based measures not defined in terms of travel time are also recommended. These measures describe how the system is performing and are useful for diagnosing problems. All three types of measures are needed to provide a complete picture of performance.

- 13 - Key Features • Traveler Focus • Multiple Facilities • Multiple Modes • Precursor to Accessibility Trip-Based Measures • Individual Facilities • Bottleneck/Problem Identification • Individual Facilities • Vehicle-Oriented • Non-travel time measures • Help to Explain Outcomes Facility-Based Measures Facility-Based Output Measures Type of Measures Travel Time Outcome Measures Segment d/c Lane-to-Lane Speed Variability VMT/PMT Queue Statistics Figure 3 – Recommended performance measure framework for different evaluation purposes