ETC Accuracy - How Accurate Should We Be?

Accuracy versus precision
Perception of accuracy
History of accuracy, transact/transponder
Pareto economic rule
Accuracy and level of effort
Anatomy of ETC accuracy
Summary

Accuracy versus Precision

Accuracy vs Precision

Perception of Accuracy
Public

Collect all the revenue (Press reports)

Private Concessions

Lack of profitability is not a public concern
Better service (express lanes, AETC) create more trips and therefore a higher net revenue

History of Accuracy
Tests by IAG, Florida, Texas etc.

Transponder read accuracy of 99.96% (4 in 10,000)

Testing focus led to accuracy interpretations in procurements
Procurement specifications began to require 99.96% accuracy which was interpreted as the transaction

Pareto Economic Rule
Vilfredo Pareto, Italian who in 1900 discovered that 20% of the people consistently controlled 80% of the wealth
Has become known as the 80/20 rule
80% work done by 20% of the people
80% value comes from 20% of the work day
X% of accuracy comes from Y% effort & $

Accuracy curve

Accuracy Curve

Anatomy of ETC Accuracy
Framing
Classification
VES
AVI
Exception processing
Transaction accuracy is the product of the component accuracies (the critical measure)

Framing
Detection, vehicle separation & associating the transponder read

Straddling
Shoulders
Associate AVI read to correct vehicle and correct image capture

Classification
AVC system accuracy
Ability of lane controller to correctly process AVC information
Fail safe audit system needed to determine this accuracy

Violation Enforcement System
Percentage of useable images

Cameras
Triggering mechanism

Percentage of images processed and verified
Lane controller processing
Customer record accuracy

AVI
Reader operation

Read vs. read-write

Transponder operation

Mounted correctly in vehicle

Lane controller processing

Exception Processing
Lane controller processing

Various modes
Closed, special events, degrade

Emergency conditions

Is 99.96% reasonable?
Certain components perhaps
Entire transaction, not likely
Varies with homogeneity of traffic and composition of vehicles
Business rules must be set to error in the favor of the customer

Why Insist on 99.96%?
Tradition evolved into a standard
Adverse to risk in the public sector
Following the lead of others

Accuracy is Facility Dependent
Nature of traffic

Mostly 2 axle vs. many trucks and types of vehicles

Type of collection system

Barrier vs. ticket

Summary
Transaction accuracy should be a conscious decision considering the components and the tolling environment
High accuracy is possible but costly.

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