Development of a Methodology for Estimating Vehicle Emissions

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Development of a Methodology for Estimating
Vehicle Emissions

• Jennifer Armstrong
• Carleton University
• August, 2000

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Presentation Overview

• Background
• Research description
• Input data preparation
• Development of tools
• Sensitivity analysis
• Vehicle emissions in the NCR
• Conclusions

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Why Model Vehicle Emissions?

• Analyze the environmental impacts of
  transportation and land use policies
• use of high-occupancy vehicle lanes
• major road network modifications
• changes in transit ridership
• Evaluate methods to improve air quality

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Automobile Pollution
Refuelling Emissions
CO2 Estimated based on fuel consumption
Two Processes Combustion (Exhaust
System) Evaporation (Fuel Storage and Delivery
System)
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Vehicle Emission Modelling

• Criteria pollutants
• Estimated using MOBILE5, an empirical model
  developed by the U.S. EPA
• Emissions Base Emission Rate Adjustment
  Factors VKT
• Greenhouse gas emissions
• Estimated based on fuel sales or assumptions of
  average vehicle fuel efficiency
• Emissions GHG emission factor fuel
  consumption rate VKT

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Input Requirements

• Emission models often require as input
• number of vehicle kilometers travelled
• average operating speed
• trip length distribution

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Travel Demand Models

• Used to predict future traffic levels based on a
  regions demographic and socio-economic
  characteristics
• Regional EMME/2 model can predict
• number of vehicles per road segment
• average operating speed
• trip length distribution

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Deficiencies of Current Practice

• Assumption of average driver behaviour and trip
  characteristics may not be universally valid
• Speed estimates from travel demand models may not
  be accurate
• Model inputs are often based on default values,
  not local conditions

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Model Integration
Emission Models
Travel Demand Models
MOBILE5
EMME/2
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Model Integration
Emission Models
Travel Demand Models
MOBILE5
EMME/2
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Research Methodology

• PREPARE INPUT DATA
• Intra-zonal travel
• Operating mode characteristics
• Commercial vehicle travel
• Vehicle age distribution
• Temperature data

• COMPUTE VEHICLE EMISSIONS
• Sensitivity tests
• Vehicle age distribution
• Operating mode fractions
• Temperature
• Trip length distribution
• Speed
• Vehicle mix
• GHG emission fractor
• Vehicle emissions in the NCR

• DEVELOP TOOLS
• EMME/2 macros
• (summarize travel data)
• The Emission Calculator
• (computes vehicle emissions)

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Study Area
Ottawa-Hull CMA Population 1 million
people Employment 500,000 jobs Land Area 5700
sq-km
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Analysis Periods

• Selected 5 analysis periods with similar travel
  characteristics

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Road Classification Scheme

• Developed a classification scheme based on
• road capacity
• local roads / centroid connectors
• major and minor arterial/collectors
• freeways and rural highways
• transit-only roads
• location within the study area
• core, urban, suburban, rural

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Intra-zonal Travel

• Trips which begin and end in the same traffic
  zone are not assigned to the transportation
  network in EMME/2
• To estimate the amount of travel associated with
  intra-zonal trips, TransCAD GIS was used to
  compute the shortest path between trip origins
  and destinations

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Intra-zonal Travel - Analysis
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Intra-zonal Travel - Results
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Background Traffic

• It is important to know the total volume of
  traffic using the transportation network
• improve travel time estimates
• improve vehicle emission estimates
• EMME/2 only predicts passenger vehicle travel

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Background Traffic

• Analyzed data from the 1996 CO counts to
  determine the amount of commercial vehicle travel
  
• Established vehicle mix ratios for freeways, and
  for arterial/collector roads in urban, suburban,
  and rural areas
• Made assumptions regarding vehicle weight
  categories and fuel types

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Background Traffic - Results
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Operating Mode Analysis

• Three operating modes
• hot start
• cold start
• hot stabilized
• If the engine has been turned off for more than
  an hour, the trip is defined as cold start

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Operating Mode - Results
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Operating Mode - Results
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Temperature Inputs

• Correspond to a typical October day
• Based on temperature data measured at the Ottawa
  Intl Airport

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Vehicle Age Distribution
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EMME/2 Macros

• Create an output file which summarizes travel
  data (vkt, link speed, trip length distribution,
  ...)

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The Emission Calculator

• Computes CO, NOX, and HC emissions using MOBILE5

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The Emission Calculator

• Computes greenhouse gas emissions using fuel
  consumption equations specified by the user

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The Emission Calculator
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The Emission Calculator
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The Emission Calculator
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Daily Vehicle Emissions
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Daily Vehicle Emissions
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Vehicle Emissions in the NCR
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Vehicle Emissions in the NCR
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Vehicle Emissions in the NCR
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VOC Emissions
PM Peak Hour
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NOX Emissions
PM Peak Hour
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Benefits of Research

• Development of tools to compute vehicle emissions
• Estimation of vehicle emissions in NCR
• Sensitivity analysis of input parameters
• Illustration of a potential application of GIS in
  transportation planning
• Analysis of intra-zonal trips, commercial vehicle
  traffic, operating mode fractions

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Research Limitations

• Ignored seasonal variation in emissions
• Missing or incomplete data
• vehicles with catalytic converters
• linked trips
• external trips
• vehicle age distribution
• fuel consumption equations
• Estimation of 2021 emissions ignored changes in
  vehicle technology
• Lack of speed post-processing

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Recommendations

• Consider seasonal variation in emissions
• Update Emission Calculator for use with MOBILE6
• Compare MOBILE5 and MOBILE6 results
• Develop speed post-processors
• Revise fuel consumption equations
• Expand questions in OD Survey
• Consider the impact of future technology
• Comparison / validation of results