Transportation leadership you can trust.

presented to

Talking Operations Webinar

presented by

Richard MargiottaCambridge Systematics, Inc.

June 28, 2006

Uses of Travel Time Reliability

2

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

3

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!

4

So Why Do Travel Times Vary?

Seven Sources of Unreliability

1. Traffic incidents

2. Special events

3. Work zones

4. Weather

5. Day-to-day demand (volume) fluctuations

6. Traffic control devices (railroad crossing, poor signal timing)

7. Inadequate base capacity

5

A Model of Congestion and Its Sources

n = Source of Congestion= Source of Congestion

Base DelayBase Delay(“Recurring” or “Bottleneck”)(“Recurring” or “Bottleneck”)

PhysicalPhysicalCapacityCapacity

……interacts withinteracts with…… DemandDemandVolumeVolume4

6

A Model of Congestion and Its Sources

n = Source of Congestion= Source of Congestion

Base DelayBase Delay(“Recurring” or “Bottleneck”)(“Recurring” or “Bottleneck”)

PhysicalPhysicalCapacityCapacity

……interacts withinteracts with…… DemandDemandVolumeVolume4

Daily/SeasonalDaily/SeasonalVariationVariation

SpecialSpecialEventsEvents

PlannedPlanned

……determinedetermine……EmergenciesEmergencies2 3

7

A Model of Congestion and Its Sources

n = Source of Congestion= Source of Congestion

Base DelayBase Delay(“Recurring” or “Bottleneck”)(“Recurring” or “Bottleneck”)

PhysicalPhysicalCapacityCapacity

……interacts withinteracts with…… DemandDemandVolumeVolume

Daily/SeasonalDaily/SeasonalVariationVariation

SpecialSpecialEventsEvents

PlannedPlanned

……determinedetermine……EmergenciesEmergencies2 31

……lowers capacitylowers capacityand changes demandand changes demand……

Traffic ControlTraffic ControlDevicesDevices

Roadway EventsRoadway Events

WeatherWeather

IncidentsIncidents

WorkWorkZonesZones

5

6

7

…can cause…

…can cause…

…can cause…

8

A Model of Congestion and Its Sources

n = Source of Congestion= Source of Congestion

Base DelayBase Delay(“Recurring” or “Bottleneck”)(“Recurring” or “Bottleneck”)

PhysicalPhysicalCapacityCapacity

……interacts withinteracts with…… DemandDemandVolumeVolume4

Event-RelatedEvent-RelatedDelayDelay

TotalTotalCongestionCongestion

Daily/SeasonalDaily/SeasonalVariationVariation

SpecialSpecialEventsEvents

PlannedPlanned

……determinedetermine……EmergenciesEmergencies2 31

……lowers capacitylowers capacityand changes demandand changes demand……

Traffic ControlTraffic ControlDevicesDevices

Roadway EventsRoadway Events

WeatherWeather

IncidentsIncidents

WorkWorkZonesZones

5

6

7

…can cause…

…can cause…

…can cause…

9

Effects of Incidents and Weather on Reliability

10

Changes in a High Growth Corridor

11

Use of Reliability: Congestion by Source

Where should we be concentrating our resources and effort?

• National programs

• State programs

• Corridor-specific programs

12

Current Estimates of Delay by Source: National

13

Some Empirical Results (Freeway Corridors)

Los Angeles

Seattle

San Francisco

Albany

Recurring 69% 71% 80% 72%

Incident 31% 16% 13% 28%

Work Zone 0% 0% 0% Not inc.

Weather 0% 9% 2% Not inc.

Special Ev. 0% Not inc. 5% Not inc.

High Vol. Not inc. 4% Not inc. Not inc.

14

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

15

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

I-75 SB, 1/24/2002 (Thurs)

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

4:00 PM 4:29 PM 4:58 PM 5:26 PM 5:55 PM 6:24 PM

Average

Today

95th %ile

16

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

17

Overall Reliability

• Travel conditions are unreliable (Variable over time)

USED BYMEASURESWHAT THEY TELL YOU

• Upper Management• Public Relations• Planners

Delay by Source

e.g., vehicle-hours

• What’s causing unreliable travel (e.g., incidents, weather, work zones)

• Mid-Management• Operators• Planners

Work Zones WeatherSpecial Events Incidents Traffic

ControlDemand-

VariabilityBase

Capacity

Activities, Procedures, and

Policies

• What aspects of operations, management, and construction need to be improved

• Operators• Field Managers

… for incidents …

e.g., buffer index

INCIDENT TIMELINE

Incident Occurs

Incident Recorded into

CAD (Detection)Incident Verified

Personnel Dispatched and Actions Initiated

Responders Arrive to

Scene

Incident Cleared and Actions Canceled

Return to Normal

Conditions

6:35 A.M. 6:42 A.M. 6:47 A.M. 6:49 A.M. 6:50-7:00 A.M. 7:15 A.M. 8:26 A.M.

1 2 3 4 5 6

Detection Time

Verification Time

Dispatch Time

Response Time

Clearance Time

Time to Normal

Conditions

Level 1

Level 2

Level 3

18

19

20

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”

21

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

22

Relationship Between Reliability and Congestion Level

23

24

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)

25

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/