Wireless connectivity would enable roadway users to receive information to provide 360° situational awareness. In unsafe situations, IntelliDriveSM applications provide alerts and advisories, or take action to help roadway users avoid or mitigate crashes.
Travel Time Reliability Brandon Nevers, P.E., PTOE March 4, 2010
Sally lives 10 miles from work. Without any traffic it takes her 15 minutes door-to-door. On a normal day during rush hour it takes her about 25 minutes . On a bad day when there’s an incident or bad weather or something else, it takes her up to 40 minutes .
WHEN SHOULD SALLY LEAVE TO ARRIVE ON TIME?
Day-to-Day Variations in Travel Time Source: http://ops.fhwa.dot.gov/publications/tt_reliability/TTR_Report.htm
Factors Contributing to Reliability Operational Effect Special Events Reduced Lanes Poor Signal Timing Weather Work Zones Incidents Recurring Congestion Increased Demand Reduced Lane Capacity
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
A variety of reliability performance measures have been defined and applied (no single metric)
The appropriateness of a reliability measure or set of measures is dependent on the application
Reliability measures do not address the productivity of our networks
Reliability measures generally relate travel time from a “bad day” to a normal or expected delay
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
Graphical Illustration of Reliability Measures Source: http://ops.fhwa.dot.gov/publications/tt_reliability/TTR_Report.htm
What is the most effective way to measure reliability?
What data do I need and where/how do I get it?
What is a “desirable” or “acceptable” reliability measure?
How should reliability measures be weighed against traditional measures (i.e., Level of Service)?
Florida Department of Transportation Central Office
Conducted pilot project to determine feasibility of adding reliability to existing reporting efforts
Evaluated freeway system statewide
Developed hourly travel time profiles using ATR volume data
Next steps: incorporating real-time data and incident data
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
“ Regional transportation systems management and operations (TSM&O) means an integrated program to optimize the performance of the existing infrastructure though implementation of multi-modal, cross-jurisdictional systems, services, and projects.” – FHWA
Four key elements:
Traveler Information Source: http://www.maps.google.com Better Traveler Information Improved Trip Decision Making Increased Capacity Utilization & Reliability
Vehicle and Infrastructure Technology = Source: http://www.its.dot.gov/strat_plan/strategic_plan2010_2014/
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
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
Benefit-Cost Analysis of Ramp Metering on SR 520 Floating Bridge for AM Peak (Seattle, WA)
Source: ECONorthwest 6.6: 1 Benefit-Cost Ratio $78,000 Total Cost (5 yrs) $112/mi Value of Reliability for Improvement 0.15 min/mi .20 min/mi Certainty Equivalent 0.30 0.37 Buffer Index 2.15 2.54 Planning Time Index After Before Measure