A New Approach to Assessing Road User Charges

1
A New Approach to Assessing Road User Charges

• Max Donath
• Pi-Ming Cheng
• Shashi Shekhar
• Research Project Team Meeting
• May 8, 2001

2
Requirements of DGPS Systems for Road User Charge

• Coverage
• Need national coverage
• Need to work in different environments urban,
  rural, mountainous, forestal, etc.
• Need to be reliable and robust
• Accuracy
• 1 m _at_ 1 RMS for road user charge system
• What is the acceptable tolerance for error?
• Cost
• Minimum cost for an acceptable system
• Economy of scale (cost ? when number of units ?)
• Privacy
• Broadcast correction signals to users (vehicle
  locations are not broadcast to anyone)

3
GPS Accuracy Specification
Questions 1. How close can a limited access road
be to a frontage road? 2. What is the acceptable
tolerance for error?
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Nationwide DGPS

• Converted from Coast Guard Maritime System
• 0.5 meter near the reference station and degrade
  up to 1 meter/150 km
• Typical accuracy is 1 to 3 meters
• Implementation is slow (behind schedule)
• Currently operational sites near MN Alma, WI and
  Superior, WI
• Will add carrier phase differential service in
  the future (10 cm accuracy)

Coverage originally projected by the end of 2000
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WAAS and LAAS

• WAAS covers the entire north America accuracy
  7m (horizontally and vertically)
• LAAS complements WAAS and is airport dependent
  (limited coverage)
• LAAS has an accuracy of 1m or less

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NASA JPL Global DGPS System

• Global coverage, predicted accuracy 10 cm
  (static accuracy)
• System model corrects for
• GPS satellites orbital and clock errors
• tropospheric delay
• Only works with dual-frequency GPS receiver
  (intrinsically corrects for ionospheric errors)
• Can be used for real-time positioning at 1 Hz
• Eliminates the need for setting up local GPS
  reference stations
• Software cost 115K for executables and 230K
  for source code
• Problems cost of dual-frequency receivers,
  infrastructure to broadcast correction signals

broadcast
Internet
or
wirelessly transmitted correction signals to
vehicles
wireless internet
computer server
NASA Global GPS Network
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OmniSTAR

• Covers the entire north America
• Accuracy 50cm _at_ 1 RMS, 1m _at_ 2 RMS
• High reliability (99.7 in 1998)
• 24x7 customer service
• Requires an OmniSTAR box (processor) per GPS
  receiver
• Subscription fee 800/year
• Work mostly with high-end receivers
  (OmniSTAR-enabled GPS receivers ? 3,000 5,000)

AMSC L-Band Satellites cover the entire US
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Trimble Virtual Reference Stations

• High accuracy (
• Requires a base station every 20 30 miles in
  radius
• Does not need FCC license to broadcast correction
  signals
• Needs to send raw GPS positions to the central
  control server (privacy concerns)

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GM OnStar

• Combines GPS and wireless technologies
• Growth rate adds 2 million subscribers per year
• An on-demand system central service center does
  not track vehicles (Only when the driver presses
  the OnStar button located in the vehicle does
  OnStar know the location. OnStar also knows the
  vehicle location if the air bags deploy or if the
  driver reports the car stolen).
• Privacy provides vehicle information to 911,
  police, fire, ambulance or roadside-assistance
  providers at the drivers request only (also
  requires PIN for authorization)

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Dynamic DGPS Performance Evaluation

• DGPS receivers generally do not have
  specifications on dynamic accuracies
• Important to determining a vehicles position
  while traveling at high speed
• In order to evaluate DGPS systems, the
  measurement system must be able to provide
  resolution on the order of 2 cm or better
• Our group evaluated dynamic performance of a
  Novatel RT-20 system in 1996

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Dynamic DGPS Performance Evaluation Setup

• Camera Computer controlled shutter triggered to
  minimize latency
• Inertial Measurement Unit (IMU) Determines pitch
  and roll angles to avoid geometric errors

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Dynamic DGPS Performance Evaluation block diagram
RF Modem Antenna
Correction from base station
RF Modem
Correction
GPS Antenna
Position of Antenna and Camera
COMPUTER
Serial Line
GPS
Timing Line
Mast for common vertical axis
Computer Hard Drive
Synchronization
Image Grabber
Digital Camera
To shutter
Camera Controller
Analog to Digital Converter
Inertial Measurement Unit
Roll, Pitch
Tile representing ground truth
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GIS For Road User Charge System Goals

• Evaluate ability of GIS roadmap databases
• Meet requirements of road user charge system
  accuracy, coverage
• Recommend a cost-effective application for phase
  II

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Digital Road Maps

• Sources for digital road maps
• Basic data - USDOC TIGER files
• Cleaner maps - urban (Navtek, Etak), rural (GDT)
• Relevant Layers
• Economic attributes - administration zone(s),
  congestion zones
• Geographic locations - latitude, longitude,
  altitude
• Route attribute - name, type, time restrictions
• Route segment - direction, type (e.g. bridge),
  restrictions
• Routing attributes - intersections, turn
  restrictions

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Quality Metrics

• Framework
• Compare with a reference (gold standard) source
• Example aerial photographs, GPS, field surveys,
  ...
• Road map quality metrics
• Accuracy - how close is map information to
  actual?
• Coverage - how complete is the map information?
• Currency - how current is the map?
• Costs - initial cost, periodic update cost, ...

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Assessment Framework

• Static assessment
• Compare with relatively static reference map
• Example aerial images, reference databases
• Relevant for economic attributes (e.g.
  administrative zones, congestion zones),
• Dynamic Assessment
• Compare with dynamic location source, e.g.
  high-accuracy GPS receivers on vehicles

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Subtasks for GIS

• Design and Evaluation of GIS Databases
• Identify data sources to get relevant content
  layers
• Evaluate accuracy, coverage, currency, costs
• Develop guidelines for requirements
• Specify hardware requirements
• Develop update procedures

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Integration of GPS/GIS

• Different configurations of integrated GPS/GIS
  systems

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On-Board Weighing System
Display
Trailer Load Coder
Trailer Load Coder
5th Wheel Weighing System
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Specifications of the On-board Weighing System
for Road User Charge

• Different trucks have different configurations ?
  require different weighing systems
• Accuracy (accuracy ? cost) Is an error of 200
  300 lbs acceptable?
• Capacity (static, dynamic, and safe overload)
• Sensitivity
• Reliability and robustness
• When to measure (not all trailers have doors)?
• Meet the need for law enforcement
• Testing facility Mn/Road - different road
  surfaces

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Timeline
Feb 01
Dec 01
1. GPS subsystem
design
evaluation
Jun 01
Jun 02
Jun 01
Feb 02
Aug 02
design
2. GIS subsystem
evaluation
Aug 01
Update proc.
Jun 02
Dec 02
Jul 01
Oct 01
design
3. Weighing system
testing
Aug 01
May 02
4. System Integration
Mar 02
Dec 02
5. Report
JanFeb 03
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Wireless Data Transmission
? Wireless data transmission is not part of the
Road User Charge Project Phase I