The document discusses travel time reliability, including how it is defined, measured, and improved. It describes how reliability focuses on reducing variability in travel time rather than just reducing travel time. Various reliability measures are presented such as buffer time, buffer index, and planning time index. Ways to improve reliability include traveler information, vehicle technologies, incident management, and performance improvement strategies. Case studies demonstrate how reliability can be analyzed and quantified.

1. Travel Time Reliability Brandon Nevers, P.E., PTOE March 4, 2010

5. Day-to-Day Variations in Travel Time Source: http://ops.fhwa.dot.gov/publications/tt_reliability/TTR_Report.htm

6. Factors Contributing to Reliability Operational Effect  Special Events   Reduced Lanes  Poor Signal Timing  Weather  Work Zones  Incidents  Recurring Congestion Increased Demand Reduced Lane Capacity

7. How is Reliability Different? Full Distribution Average Statistical Reporting Yes No Demand Effects Considered? All Recurring Type of Congestion Accounted For Multiple days Single Day Temporal Analysis Period Path/Network Point Spatial Element Analyzed Reliability-Focused Analysis Approach Traditional Analysis Approach

10. Commonly Applied Reliability Measures The amount of buffer time required The difference between the 95 th percentile travel time and the average travel time Buffer Time Description Definition Measure The size of the buffer as a percentage of the average The 95 th percentile travel time minus the average travel time divided by the average travel time Buffer Index How much larger the potential total travel time is than the ideal or free-flow travel time The ratio of the Planning Time to the Ideal or Free Flow Travel Time Planning Time Index The total travel time required to arrive on-time 95% of the time 95 th percentile travel time Planning Time

11. Graphical Illustration of Reliability Measures Source: http://ops.fhwa.dot.gov/publications/tt_reliability/TTR_Report.htm

14. FDOT Pilot Study (Sample Results for I-95) 55% 59% 26 40 SR 708 US 98 126% 76% 17 39 US 98 SR 869 25% 37% 30 38 SR 869 I-595 56% 59% 25 39 I-595 FLA Turnpike 41% 50% 27 39 FLA Turnpike SR 924 97% 73% 21 42 SR 924 I-195 43% 47% 23 33 I-195 Dolphin Expy 137% 79% 17 41 Dolphin Expy SR 5 Buffer Index % Time the avg speed is < 10 mph less than uncongested speed 95 th % Speed (mph) Average Speed (mph) To From

16. BH Highway Corridor Travel Times Ideal 95th Free-flow Average 95 th Percentile Free Flow = 4.5 min Average = 6.2 min 95 th Percentile = 9.6 min Planning Index = 2.1 Buffer Index = 0.54

17. How can Reliability be Improved? TSM&O Travel Time Information Vehicle & Infrastructure Technology Incident & Event Management Performance Improvements

19. Traveler Information Source: http://www.maps.google.com Better Traveler Information Improved Trip Decision Making Increased Capacity Utilization & Reliability

20. Vehicle and Infrastructure Technology = Source: http://www.its.dot.gov/strat_plan/strategic_plan2010_2014/

22. Performance Improvement Strategies Reduce and encourage alternative travel Travel reduction Multimodal travel Low-cost changes to the physical roadway section Lane treatments Access management Geometric design treatments Strategies that influence and respond to demand Congestion pricing Variable speed limits Traffic demand metering Signal timing/ITS

23. Non-Lane Widening Strategies to Improve Capacity Interchange Modifications VMS/DMS Alt LT Treatments Frontage Road In-Vehicle Info Right/Left Turn Channelization Weaving Section Pre-Trip Information Access Points HOT Lanes Truck Restrictions Raised Medians Pricing by Distance Truck Only Lanes Queue Management Congestion Pricing Variable Lanes Adaptive Signals Ramp Closures Reversible Lanes Signal Coordination Ramp Metering Narrow Lanes Signal Retiming HOV Lanes Both Arterial Freeway

25. Brilon and Geistefeldt. Implementing the Cost of Reliability for Highway Capacity Analysis, 56 th TRB Annual Meeting, Washington DC

28. Truck Restricted Lane Modeling Results General Purpose Lanes Truck Restricted Lanes 0.67 0.2 35 6.9 3840 48 Avg Strategy 0.4 55 11.6 4155 68 95 th % 0.20 0.50 Buffer Index 0.4 29 8.2 3105 63 95 th % 0.2 24 6.9 2920 46 Avg 0.8 0.4 Queue Length (mi) 51 36 Density (pc/mi/ln) 13.4 8.9 Travel Time (min) 6836 6502 VMT (veh*mi/15 min) 44 35 Speed (mph) 95 th % Avg MOE Baseline

29. Truck Restricted Lane Analysis Results

31. Certainty-Equivalent Approach Process