to jun 28 06 rm

Uses of Travel Time Reliability: 

presented to Talking Operations Webinar presented by Richard Margiotta Cambridge Systematics, Inc. June 28, 2006 Uses of Travel Time Reliability

Why is Reliability Important?: 

Why is Reliability Important? Reliability is an indication of how travel times vary from day-to-day … OR … How consistent is travel? How predictable is travel? Variability in travel times means that extra time must be planned for (the aforementioned Buffer). In other words, travelers have to leave earlier to account for the Buffer

Why is Reliability Important? (cont.): 

Why is Reliability Important? (cont.) The Buffer has costs associated with it Planned extra time at least as costly as regular travel time Some studies place the Buffer’s costs at 2-6 times higher than average travel time Some trips will still exceed the Buffer – late penalties Some trips will take much less than the Buffer – early arrival penalties Reliability (or the lack of it) just says that travel times are inconsistent/variable – it doesn’t tell you why!

So Why Do Travel Times Vary?: 

So Why Do Travel Times Vary? Seven Sources of Unreliability Traffic incidents Special events Work zones Weather Day-to-day demand (volume) fluctuations Traffic control devices (railroad crossing, poor signal timing) Inadequate base capacity

A Model of Congestion and Its Sources: 

A Model of Congestion and Its Sources n = Source of Congestion …interacts with… 4

A Model of Congestion and Its Sources: 

A Model of Congestion and Its Sources n = Source of Congestion …interacts with… 4 Planned …determine… Emergencies 2 3

A Model of Congestion and Its Sources: 

A Model of Congestion and Its Sources n = Source of Congestion …interacts with… Planned …determine… Emergencies 2 3 1 …lowers capacity and changes demand… Traffic Control Devices Roadway Events Weather Incidents Work Zones 5 6 7 …can cause… …can cause… …can cause…

A Model of Congestion and Its Sources: 

A Model of Congestion and Its Sources n = Source of Congestion

Effects of Incidents and Weather on Reliability: 

Effects of Incidents and Weather on Reliability

Changes in a High Growth Corridor : 

Changes in a High Growth Corridor

Use of Reliability: Congestion by Source: 

Use of Reliability: Congestion by Source Where should we be concentrating our resources and effort? National programs State programs Corridor-specific programs

Current Estimates of Delay by Source: National: 

Current Estimates of Delay by Source: National

Some Empirical Results (Freeway Corridors): 

Some Empirical Results (Freeway Corridors)

The Effect of Treating Unreliability: I-75 Central Atlanta, 2002, SB, 4-7 PM: 

The Effect of Treating Unreliability: I-75 Central Atlanta, 2002, SB, 4-7 PM

Operator’s View of Reliability: What’s Happening Now Compared to “Normal”: 

Operator’s View of Reliability: What’s Happening Now Compared to “Normal”

Use of Reliability: Performance Measurement: 

Use of Reliability: Performance Measurement Part of a comprehensive program to monitor congestion trends and operational effectiveness Can be applied at management, planning, and operations levels

Other applications/studies: 

Other applications/studies Goods movement study, Southern CA Assoc. of Governments “Travel time reliability at international border crossings,” FHWA “Travel times in freight-significant corridors,” FHWA National Transportation Operations Coalition SHRP II: “Providing a Highway with Reliability Travel Times”

SCAG Goods Movement Study: 

SCAG Goods Movement Study Speed Trucking Industry Value-of-Time: $25 to $200 per hour depending on cargo Analysis Assumption: $73 per hour (2005 $) Reliability Unexpected delays can increase Value-of-Time by 50 to 250 percent

Relationship Between Reliability and Congestion Level: 

Relationship Between Reliability and Congestion Level

SHRP II Research Program: 

SHRP II Research Program Reliability one of four SHRP II Program Areas (along with “Renewal”, “Safety”, and “Adding New Capacity” Four Reliability topic areas Building a Foundation and Institutional Setting for Operations (5 projects) Tools and Techniques for Advancing Operations (4 projects) Integrating Operations into Agency Decision-Making (2 projects) Developing Improved Operational Strategies (5 projects)

Resources: 

Resources FHWA Traffic Congestion and Reliability Report http://www.ops.fhwa.dot.gov/congestion_report/index.htm NTOC http://www.ntoctalks.com/action_teams/perf_measure.php NCHRP 3-68, Freeway Performance Measures (Fall 2006) WSDOT Activities http://www.wsdot.wa.gov/Accountability/