SHRP2 Project L08 – Incorporation of Travel Time Reliability into the HCM for Freeway

1. SHRP2 Project L08 – Incorporation of Travel Time Reliability into the HCMfor Freeway

2. objectives • incorporate non-recurring congestion(incidents, weather, work zones, special events etc.) impacts into the 2010 HCM procedure • expand the analysis horizon from a single study period (typically an AM or PM peak period) to an extended time horizon of several weeks or months to assess the variability in the quality of the facility service • develop methodologies to predict travel time reliability on selected types of facilities

3. definition of reliability • quantify the variation in travel times over time (e.g., hour-to-hour, day-to-day) • the entire range of travel times for a given trip, for a selected time period (for example, the pm peak hour during weekdays), and over a selected horizon (for example, a year) • a “trip” :a specific segment, any subset of the transportation network, or a traveler’s initial OD. • a sufficient history of travel times should be presented in order to track travel time performance • one year is generally long enough to capture nearly all of the variability

4. definition of reliability • reliability measures are quantified from the distribution of travel times • standard statistical measures (e.g., standard deviation, kurtosis) • percentile-based measures (e.g., 95th percentile travel time, Buffer Index) • on-time measures (e.g., percent of trips completed within a travel time threshold) • failure measures (e.g., percent of trips that exceed a travel time threshold) • The reliability of a facility or trip can be reported for different time slices, e.g., weekday peak hour, weekday peak period, and weekend.

5. definition of reliability-Terms • Analysis period: the smallest time unit for the HCM analysis (15 min) • Study period: the sum of the sequential analysis periods (max. 6 h) • Reporting period: the period over which reliability is to be estimated (max. 1 year)

6. definition of reliability-methods • manual methods • roadway method: equipment placed at the endpoints detects the times that an individual vehicle passes the points, for example toll tag readers, Bluetooth etc. • vehicle-based methods: equipment on the vehicle is capable of detecting and transmitting the vehicle’s time and location , for example GPS • indirect method: use spot measurements of speeds from roadway detectors on uninterrupted flow facilities

7. literature review • international research • Great Britain • Sweden • Japan • Netherlands • u.s. research • California • Florida • Nevada • SHRP2 Project L03, NCHRP Project 3-97 • FHWA ATDM Evaluation Guidebook

8. literature review • FHWA ATDM Evaluation Guidebook • Active Transportation and Demand Evaluation (ATDM) • Basic performance measures : • Vehicle-Miles Traveled Demand (VMT-Demand) • Vehicle-Miles Traveled Served (VMT-Served) • Vehicle-Hours Traveled (VHT) • Vehicle-Hours Delay (VHD) • Measures of Effectiveness (MOEs): • System Efficiency: Average System Speed (mph) • Traveler Perspective: Vehicle-hours Delay/Trip (VHD/VT) • Reliability: Planning Time Index (PTI)

9. methodology • three primary components: a data depository, a scenario generator and a computational procedure Freeway Reliability Methodology Framework

10. Methodology-data depository • at a minimum: seed file • all segment geometrics, free flow speeds, lane patterns and segment types • demands: measured for a sample of days from field sensors, or estimated from projections of AADT and time-based factors • non-recurring congestion effects • the variations in source type, the probability of its occurrence during the reliability reporting period, and its potential impacts on segment free flow speed, traffic demand, and segment capacity. • the reliability methodology relies on the availability of both facility-specific data elements and default values when data are not available, nonexistent (future analysis), or too expensive to collect.

11. Methodology-scenario generator • operate with minimal input (i.e. uses defaults) when data are not there, and accepts facility-specific data if available • demand variability • entered by time of day, day of week, and month of year • capacity variability • weather, incidents, work zones, and special events • generating scenarios • assume that non-recurring congestion events are independent of each other, the probability of an event combination is equal to the product of their two probabilities.

12. Methodology-scenario generator

13. TOOL-FREEVAL-RL • not intended to produce travel times for individual vehicles. Instead, an estimate of the mean travel time for each time (15-minute intervals) • develop Excel worksheets-based • a maximum of 70 freeway segments, a maximum duration of twenty-four 15-min time • highly recommended not exceed 9-12 mi in length • the first and last facility segments should be uncongested in the first and last time intervals to allow all queues to form and clear

14. TOOL-Input • reporting period: a minimum of 100 days recommended • baseline data • Segment Speed(mph): 15-min Free flow(vph), Space mean • Segment Density (veh/mi/lane) • Segment(Ramp) capacity (vph),demand (vph),volume served (vph) • Ramp-to-Ramp demand (vph) • Queue length at end of time interval (ft) • Estimated denied entry queue length (ft.) • extensive databases • demand variability, weather impacts and incident probabilities

15. TOOL-Input • Geometric data • Segment length (ft.) • number of lanes • free-flow speed (mi/h) • segment demand (veh/h) • % trucks • % RVs • basic, on-ramp, off-ramp,weaving, or overlapping ramp segment,other facility-wide parameters.

16. TOOL-Input • Non-recurrent congestion source • weather • A weather event (normal, rain, snow, etc..) • Duration of weather event when present • Start time of the weather event • incident • An incident event (none, shoulder closure, x lanes closed, etc.) • Duration of the incident event when present (low, med or high) • Start time of the incident event Location of segment with incident • Factors • PHF • DMs • CAF,SAF,DAF

17. TOOL-Output • HCM performance measures • Mean TTI across all scenarios • Facility Mean Speed (mph) • PTI (95% percentile TTI) p33 • Reliability Rating (% VMT Served @ TTI <1.33) • Misery Index (mean of worse 5%TTI) • Mean VHD in a 3hr study period • % VHD Due to Non-Recurring Effects • VMTD Veh-miles / interval (Demand) p37 • VMTV Veh-miles / interval (Volume served) • VHT travel / interval (hrs) • VHD delay /interval (hrs)

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21. TOOL Report

22. THANK YOU