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33 sensitive, however, to unanticipated delay caused by inci- Safety performance measurement is advanced in other dents, construction, weather, demand fluctuations, special developed nations. An international scan of performance- events, traffic control devices, or inadequate base capacity. based planning found Australia, New Zealand, British Colum- Industry has largely turned to just-in-time production and bia, Canada, and Japan to have particularly advanced safety delivery methods, and similarly it can accept anticipated performance measurement regimes. The team contributed delays. But variability in travel times can significantly delay the successes of these countries to their ability to: shipments beyond expected delivery times (Harrison et al., 2006). Because the highway system is mature, transportation · Understand underlying safety problems; improvements result in increasingly smaller marginal improve- · Establish institutional leadership and accountability; ments in average travel times. Thus, importance of system · Define safety performance measures and targets; reliability is increasing relative to the importance of average · Collect and analyze data; travel time (Cambridge Systematics, Inc., 2000; Cambridge · Benchmark results against other agencies; and Systematics, Inc., 2007). · Integrate results into agency decision making (McDonald Measures of mobility and accessibility are distinct but et al., 2004). complementary. Mobility represents the ability to travel (e.g., travel time, travel rate); accessibility is the ability to reach In the United States, performance measurement is a key desired destinations or activities. Measures of accessibility focus of the Integrated Safety Management System, a system generally address issues such as: for bolstering highway safety by integrating the disciplines of numerous public agencies (Bahar et al., 2003). · Access of persons/households to jobs (e.g., employment opportunities within 30 minutes); Transportation Performance · Access of employers to labor force (e.g., workers within Factors and Measures 30 minutes); In evaluating major capacity expansion projects, impacts on · Access of persons to other opportunities (e.g., shopping, the movement of people and goods over that system are among school, daycare); and the most common considerations. The performance mea- · Access of persons to alternative modes of transportation, sures framework identifies four categories for evaluating the especially transit (e.g., population within one-quarter mile impact of capacity-adding projects on transportation system of a transit stop). performance. There are five categories of accessibility measures: · Mobility; · Reliability; 1. Isochronic (or cumulative) opportunity that measures the · Accessibility; and number of opportunities (e.g., jobs) within a given travel · Safety. time; 2. Gravity-based measures that weight opportunities by time/ Mobility distance; Mobility refers to the ability of the transportation system to 3. Utility-based measures that weight opportunities by their facilitate efficient movement of people and goods. Mobility relative importance/benefit; typically addresses recurring congestion that results when 4. Constraints-based measures that introduce temporal traffic volumes approach or exceed available roadway capac- feasibility; and ity. Mobility measures do not capture the implications of the 5. Composite accessibility measures that combine features of location of the congestion compared to desired destinations, several of the above measures. but instead simply highlight the extent of congestion in comparison with free-flow conditions. Research efforts continue to investigate how to integrate Two guiding objectives were identified for mobility: accessibility measures into planning and monitoring efforts (Chen et al., 2007; Bhat et al., 2006; Levinson and Krizek, 2005). · Reduce recurring congestion improve travel time; and A new measure, "Place Rank," is inspired from a methodol- · Reduce traffic volume. ogy used in ranking web pages for the Google search engine. It takes advantage of origin and destination information and Table 4.1 presents seven broad performance measures to can be implemented without knowing point-to-point travel address these objectives and specific applications of each time (El-Geneidy and Levinson, 2006). performance measure. The case study highlight illustrates
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34 SHRP 2 Framework Measure Specific Measure Applications Recurring Delay Difference between the actual time · Average daily traffic flow per freeway lane; required by motorist to traverse a roadway segment · Ton-miles traveled by congestion level; and the unconstrained time. · Delay per ton-mile traveled; · Lost time due to congestion (per vehicle or experienced by all vehicles); · Vehicle queuing and its relationship to overall delays; · Percentage of time average speed is below threshold value; · VMT by congestion level; and · Percentage of congested miles of state-maintained highways by area (urban, rural), functional class (interstate, priority, etc.). Trip Travel Time Time required for a motorist to com- · VHT per capita; plete a trip from its origin to its destination. · VHT per employee; and · Average person hours of travel (PHT). Travel Time Index Ratio of the actual travel time for a · Mobility index [person-miles (or ton-miles) of travel/vehicle-miles of travel trip compared to the unconstrained travel time. (PMT/VMT) times average speed]. Volume to Capacity Ratio Actual number of vehicles · Percent of VMT which occurs at facilities with a V/C ratio greater than 0.71 or using a roadway segment relative to the number of 0.8 (or another threshold); and vehicles it is designed to handle over a fixed time · V/C by route. period. Level of Service Qualitative letter grade of highway · Percent of highways not congested during peak hours; and operating conditions from A (unconstrained travel) to F · Number and percent of lane-miles congested. (severe congestion). Vehicle Miles Traveled Number of vehicles traveling a · Total VMT; specified portion of the highway network over a set · VMT growth relative to population, employment; time multiplied by its length in miles. · VMT per capita; · VMT per employee; · VMT within urban areas; · Average person miles of travel (PMT); · PMT per capita; · PMT per worker; and · Delay per VMT (by mode) Mode Share Number of percent of transportation system users using non-SOV travel means (e.g., transit, bicycle, high-occupancy vehicle travel). Case Study Highlight: Mn/DOT 2003 Statewide Transportation Plan Description: Minnesota's 2003 Statewide Transportation Plan and 2005 district-level plans comprise one of the nation's first comprehensive, performance-based state transportation planning efforts. The Statewide Plan sets a framework for long-range investment planning, with perform- ance measures and targets in 10 policy areas. The district-level plans identify investment levels needed to meet targets and detail a prioritized, fiscally constrained 20-year implementation program. The statewide and district plans serve as the critical link between Mn/DOT's strategic goals and the capital investment program in the Statewide Transportation Improvement Program (STIP). Mn/DOT employs regular performance monitoring to evaluate investment choices and adjust the state's investment program. Sample Measures: · Policy: Enhance Mobility in Interregional Transportation Corridors Linking Regional Trade Centers (RTC): Travel Speed Percent of IRC miles meeting speed targets; and Travel-Time Reliability Peak period travel time reliability. · Policy: Enhance Mobility Within Major RTCs: Travel Time Ratio of peak to off-peak travel time (Travel Rate Index); and Travel-Time Reliability Peak-period travel time reliability. Table 4.1. Transportation Measures Mobility
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35 how the Minnesota DOT incorporated many of these measures the Arizona DOT measures incident duration in their MoveAZ into their 2003 Statewide Transportation Plan. Transportation Plan. Several of these example measures have been adapted from the Reliability SHRP 2 project L03 Analytic Procedures for Determining the Reliability refers to the ability of users of the system to predict Impacts of Reliability Mitigation Strategies. the amount of time it takes to make trips on the system. Reli- ability typically addresses nonrecurring congestion that results Accessibility from traffic incidents (crashes, breakdowns, special events, weather, and construction). Factors that impact reliability Accessibility refers to the ability of the transportation system include things such as route redundancy, incident response, to connect people to desired destinations through the spatial and incident rates. Table 4.2 presents four general measures analysis of residential population, employment centers, and with examples that all support the objective of reducing non- other service or recreation opportunities. Accessibility differs recurring congestion. The case study highlight illustrates how from mobility in that the measures can consider all modes, SHRP 2 Framework Measure Specific Measure Applications Reliability Index A measure of the additional time (in · Buffer Index. The difference between the 95th percentile travel time and the minutes, percent extra time, etc.) that trips take average (or median) travel time, normalized by the average (or median) travel under congestion conditions relative to uncongested time (i.e., the percent extra time). or `normal' conditions. · Travel-Time Index (TTI). The ratio of travel under congested conditions (i.e., 80th, 95th percentile of traffic flow) to another (i.e., median, mean of traffic flow). · Planning-Time Index. 95th percentile travel-time index divided by the free-flow travel-time index. · Skew Statistic. The ratio of (90th percentile travel time minus the median) divided by (the median minus the 10th percentile). · Misery index. The average of the highest five percent of travel times divided by the free-flow travel time. On-Time Trip Reliability Share of trips between a · Percent of trips with travel times less than 10 or 25 percent higher than the specific origin and destination with travel times median travel time; below a designated threshold of time. · Percent of trips with space mean speed less than 50, 45, or 30 mph; and · Throughput Efficiency Difference between actual average speed of vehicles traversing a roadway segment and speed at which maximum throughput occurs. Incident Duration Average time elapsed from notifica- · Average time elapsed from notification of an incident until all vehicles have tion of an incident to incident clearance. moved to shoulder; · Average time elapsed from notification of an incident until all vehicles have been removed from scene; and · Average time elapsed from notification of an incident until all last responder has left the scene. Crash Analysis Identification of high crash locations · Location of highest crash rate (accidents per traffic volume); and by roadway segment. · Number of locations with crash rate higher than national average (accidents per traffic volume). Case Study Highlight: Arizona DOT MoveAZ Transportation Plan Description: MoveAZ is the Arizona DOT's current long-range transportation plan. MoveAZ was developed using a comprehensive performance- based planning effort to support a process in which needs and projects identified in the plan ultimately move to programming and development based on clearly defined metrics and project performance. A list of 20 performance measures was developed to assist in project selection and plan development. Sample Measure: · Reduction in hours of incident-related delay the total incident delay for a given district in 2002. If a project reduces incident delay below the 2002 level, it only receives that portion of the improvement to the 2002 level. Table 4.2. Transportation Measures Reliability
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36 and focus specifically on the congestion on those roadways Safety that inhibit key travel for a particular population or trip type. Safety refers to the ability for users of the system to reach their Typical accessibility objectives include: destination safely on any given trip. This is typically measured through the record of crashes or incidents along a particular · Provide residents access to regional centers; roadway or at a specific intersection. Although transportation · Provide businesses access to market resources; and projects often focus exclusively on safety, the focus in this · Improve or maintain transportation equity. framework is on the safety impacts of highway capacity expansion projects. The following two measures (Table 4.4) Table 4.3 lists five general measures that support these support the objective of improving safety. The case study objectives, including examples of each measure. The case highlight demonstrates how the Denver Regional Council of study highlight illustrates how Albany, New York's congestion Governments measures crash rates in their 2008-2013 Trans- management process measures destination accessibility. portation Improvement Program. SHRP 2 Framework Measure Specific Measure Applications Job Accessibility Number of jobs within a · Percent of population within 30 miles of employment; and reasonable travel time for a region's population. · Percent of population within 45 minutes of employment. Destination Accessibility Average travel time to · Average travel time from facility to destinations; major regional destinations. · Origin-destination travel times; · Accessibility index; · Percent of population within five miles or 10 minutes of state-aided public roads; · Average number of job opportunities close (within 20 or 40 minutes, by peak auto- mobile and peak and off-peak transit); · Average number of home-based shopping opportunities (trips attracted by stores; based on 10-minute automobile and 20-minute transit travel times); · Average number of home-based other opportunities (within 20 minutes by auto- mobile and 40 minutes by transit); · Percent of population close to a college and close to a hospital (within 20 minutes by automobile and 40 minutes by transit); · Percent of population close to a retail destination (within 10 minutes by automobile and 20 minutes by transit); · Average travel time for work trips; · Average travel time for home-based shopping trips, home-based other trips; · Average travel time to the CBD; · Percentage of population group with transit access to the CBD; · Average number of jobs accessible within 15, 30, and 45 minutes by transit and automobile; · Average number of low-income jobs accessible within 30 minutes by transit; and · Average number of schools, food stores, health services, social services accessible within 30 minutes by transit and automobile. Labor Force Accessibility Number of residents · Change in average travel time to major employment centers as result of project; within reach of the region's employers. · Change in number of employees within 45 minutes travel time to major employment centers as result of project; and · Percent of employers that cite difficulty in accessing desired labor supply due to transportation. Table 4.3. Transportation Measures Accessibility
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37 SHRP 2 Framework Measure Specific Measure Applications Market Accessibility Average travel time to market · Change in population within 45 minutes travel time to important market centers as centers. result of project; · Percent of wholesale and retail sales in the significant economic centers served by unrestricted (10-ton) market artery routes; and · Percent of manufacturing industries within 30 miles of interstate or four-lane highway. Environmental Justice Accessibility Impact · Level of access for disadvantaged populations to jobs, services, and market centers. Relative jobs, destinations, labor force, and market accessibility for environmental populations versus the general population. Case Study Highlight: Albany, NY Congestion Management Process Description: Albany's Capital District Transportation Committee uses their Congestion Management Process (CMP) to identify the regions' conges- tion management needs as part of the region's RTP. The CMP reports current values of performance measures and anticipated future values under alternative growth scenarios. These performance measures are related to transportation service (access, accessibility, congestion, flexibility), resource requirements (safety, energy, economic cost), and external effects (air quality, land use, environmental, economic). Sample Measure: · Travel Time between Representative Locations by Quickest Mode: Sample Time: State Office Campus to Northway Exit 10 (minutes, P.M. Peak). Table 4.3. (Continued). SHRP 2 Framework Measure Specific Measure Applications Safety Crashes per hundred million vehicle-miles · Accident risk index (`safety index'); traveled. · Accidents (or injuries of fatalities)/PMT; · Fatality (or injury) rate of accidents; · Hazard index (calculated based on accidents per VMT by severity); and · Number of accidents per ton-mile traveled. Crashes Absolute number of crashes over time · Accident rate, deaths, injury, property loss by type of corridor; (e.g., per year). · Average duration of accidents; · Number of pedestrian accidents (or injuries or fatalities); and · National rank for accident, injury, fatality rates. Case Study Highlight: Denver Regional Council of Governments FY 08-13 TIP Description: DRCOG's project evaluation process for its latest Transportation Improvement Program (FY 2008-2013) includes a unique scoring system for each type of project, including roadway capacity. The scoring system is categorized into 10 topics: current congestion, safety, cost- effectiveness, condition of major structures, long range plan score, transportation system management, multimodal connectivity, matching funds, project-related Metro Vision implementation and strategic corridor focus, and sponsor-related Metro Vision implementation. Each cate- gory has a unique scoring system, and receives up to 15 points depending upon how that category is weighted. Project sponsors submit their project online, complete this ranking process, and are given an instant score. This gives them a sense of how their project will compare to others, and what areas they need to improve in order to increase the chances for funding. Sample Measure Based on the project's estimated crash reduction and weighted crash rate in comparison to the statewide average, up to 5 points will be awarded: · Using the estimated number of crashes reported by the applicant for the three-year period, the funding request application program will convert that to a per-mile basis and will assign the crash reduction level as follows: Low (9 or fewer crashes eliminated per mile); Medium (10-19); High (20-29); and Very High (30 or more). Table 4.4. Transportation Measures Safety