Impacts of Transportation Interventions on Air Quality

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Transportation DecisionTransportation Decision--making making ––Principles of Project Evaluation and ProgrammingPrinciples of Project Evaluation and Programming

Impacts of Transportation Interventions on Impacts of Transportation Interventions on

Air QualityAir Quality

KumaresKumares C. Sinha and Samuel LabiC. Sinha and Samuel Labi

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Today’s Conversation …Today’s Conversation …

Air Pollutants Air Pollutants –– Types, Sources, and TrendsTypes, Sources, and Trends

Pollutant EmissionsPollutant Emissions

Pollutant Dispersion and ConcentrationPollutant Dispersion and Concentration

Air Quality LegislationAir Quality Legislation

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Air Pollutants Air Pollutants –– TypesTypes, Sources, and Trends, Sources, and Trends

CO -- Carbon Monoxide

HC -- Hydrocarbons

SOx – Sulfur oxides

NOx – Nitrous Oxides

Particulate matters -- include dust & smoke

Heavy metals - Pd, Cd, Zn, and Cu

CO2 -- Carbon Dioxide (a single tank produces 300-400 pounds of CO2)

CFC -- Chlorofluorocarbons

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Air Pollutants Air Pollutants –– Types,Types, Sources, and TrendsSources, and Trends

Benzene (motor vehicles emit about 15% of world’s benzene)

Aldehydes

Asbestos

Ozone (03)

Acidic Depositions

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Air Pollutants Air Pollutants –– Types, Types, SourcesSources, and Trends, and Trends

SOURCESSOURCES-- Natural sources: volcanoes, forest fires, etc.Natural sources: volcanoes, forest fires, etc.-- ManMan--made (anthropogenic) sourcesmade (anthropogenic) sources

Stationary sources: Industrial plants, etc.Stationary sources: Industrial plants, etc.Mobile sources: transportation, etc.Mobile sources: transportation, etc.

OTHER CATEGORIESOTHER CATEGORIES–– Primary vs. SecondaryPrimary vs. Secondary

Primary pollutant: those emitted directlyPrimary pollutant: those emitted directlySecondary pollutant: those formed when PP react with other Secondary pollutant: those formed when PP react with other substances in atmospheresubstances in atmosphere

-- Criteria vs. GreenhouseCriteria vs. Greenhouse

Criteria pollutants (CO, SOX, NOX, etc)Criteria pollutants (CO, SOX, NOX, etc)Greenhouse gases (C02, CH4, CFC’s, etc.)Greenhouse gases (C02, CH4, CFC’s, etc.)

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Air Pollutants Air Pollutants –– Types, Types, SourcesSources, and Trends, and Trends

0

2

4

6

8

10

12

14

16

18

20

1970 1980 1990 1995 2000 2001 2002

Year

Emis

sion

(mill

ions

of s

hort

tons

)

Carbon Monoxide(*10)

Volatile OrganicCompounds

Nitrogen Oxides

Sulphur Dioxide

ParticulateMatter

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Air Pollutants Air Pollutants –– Types, Sources, and Types, Sources, and TrendsTrends

NOx

Transportation44%Non

Transportation56%

VOCs

Transportation37%

Non Transpor

tation63%

CO

Transportation56%

Non Transpor

tation44%

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The Process of Air PollutionThe Process of Air Pollution

Emission Dispersion Concentration

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EmissionsEmissions

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EmissionsEmissions

Definition: The discharge of pollutants into the Definition: The discharge of pollutants into the atmosphereatmosphere

Types and magnitudes of emissions depends on Types and magnitudes of emissions depends on mode, fuel type, traffic volumes, traffic speed, etc.mode, fuel type, traffic volumes, traffic speed, etc.

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Air Quality EstimationAir Quality EstimationTotal Emissions

= Emissions per vehicle per mile * number of vehicles * nr. of miles

Emissions Rate (g/veh-mile)

Can be reduced by highway improvement

- Policies that restrict tailpipe emissions

- Policies that require installation of catalytic converters

- Policies that help increase speed (speed limit increases)

- Physical projects to help increase speed, decrease congestion and delay(ITS projects, signalization, freeway patrol and incident clearance, etc.)

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Can be reduced by highway improvement

- Transit improvements help reduce auto travel

- Policies that restrict the number of vehicles in a certain area (e.g.,, congestion pricing)

BUT …

Could also be increased by a highway improvement

- Induced demand

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What Factors affect the Emissions Rate?

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Factors Affecting the Rate of Pollutant EmissionsFactors Affecting the Rate of Pollutant Emissions

Factors Affecting Emission of Vehicle Pollutants

Travel Related

Driver Related

FacilityRelated

Vehicle Related

Environmental

Engine Operating Mode Speed Level

Speed Variation

Hot StartCold StartHot Stabilized

Engineering Features

Age and Mileage MaintenanceConditionWeight andSizeEnginePower

Fuel Type Used

Ambient Temperature, Altitude, Humidity

Fuel Delivery System Emission Control System Volatility, Content of Oxygen, Lead, Sulfur

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Travel Related Factors Affecting EmissionTravel Related Factors Affecting Emission

Engine Operation ModeEngine Operation ModeCold Start: Any start of a vehicle engine taking 1Cold Start: Any start of a vehicle engine taking 1--4 hrs or later 4 hrs or later following the preceding tripfollowing the preceding trip

Hot Stabilized: Time Between Start and End of Trip Hot Stabilized: Time Between Start and End of Trip

HC, CO Emission Higher During Cold Start Compared to Hot StartHC, CO Emission Higher During Cold Start Compared to Hot Start

Speed and AccelerationSpeed and Acceleration–– Smoothness and Consistency of SpeedSmoothness and Consistency of Speed

–– HC, CO Emission High at Low SpeedsHC, CO Emission High at Low Speeds

–– Sharp Acceleration at High Speed: More HC and CO EmittedSharp Acceleration at High Speed: More HC and CO Emitted

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Emissions as a Function of SpeedEmissions as a Function of Speed

For example, for Heavy Duty Gasoline Vehicles:

By increasing urban traffic speed from 20 to 50mph, we can have a 50% reduction in CO emissions

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Facility Related FactorsFacility Related Factors–– Grade, Existence of Ramps and SignalsGrade, Existence of Ramps and Signals–– Acceleration and Deceleration LanesAcceleration and Deceleration Lanes–– Traffic Signal Coordination can result in up to 50 percent Traffic Signal Coordination can result in up to 50 percent

reduction in emissions (reduction in emissions (RakhaRakha et al. 1999)et al. 1999)

Driver Related FactorsDriver Related Factors–– Aggressive Drivers: More Frequent and Severe Accelerations Aggressive Drivers: More Frequent and Severe Accelerations

and Decelerationsand Decelerations–– Abrupt Changes in VelocityAbrupt Changes in Velocity

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Vehicle Related FactorsVehicle Related Factors–– Age, Mileage, Maintenance Condition, Weight, Size, Engine Age, Mileage, Maintenance Condition, Weight, Size, Engine

PowerPower–– Older Vehicles: More Pollutants EmittedOlder Vehicles: More Pollutants Emitted–– Heavier and Larger Vehicles Emit More PollutantsHeavier and Larger Vehicles Emit More Pollutants–– Combustion Process Depends on Engine TypeCombustion Process Depends on Engine Type

Environmental Factors Environmental Factors -- Ambient Temperature Ambient Temperature –– At Low Temperatures more time required to warm up engine; At Low Temperatures more time required to warm up engine;

Level of ColdLevel of Cold--Start Emissions IncreaseStart Emissions Increase

–– At High Temperatures, Fuel Evaporation Rate Increases; At High Temperatures, Fuel Evaporation Rate Increases; Combustive Emissions Low; Evaporative Emissions HighCombustive Emissions Low; Evaporative Emissions High

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Tools for Emissions EstimationTools for Emissions Estimation

Approaches / Techniques / SoftwareApproaches / Techniques / Software

–– Emission Models Based on Vehicle Emission Models Based on Vehicle Operating ModesOperating Modes

–– Microscopic Emission ModelsMicroscopic Emission Models

–– Fuel Based Emission ModelsFuel Based Emission Models

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Tools for Emissions Estimation Tools for Emissions Estimation –– The MOBILE6 SoftwareThe MOBILE6 Software

Software Development was Sponsored by: EPA Software Development was Sponsored by: EPA

Pollutants: CO, HC, Pollutants: CO, HC, NOxNOx

Vehicle Classifications: 28Vehicle Classifications: 28

Roadway Facilities: Freeways, Arterial/Collectors, Local Roadway Facilities: Freeways, Arterial/Collectors, Local Roadways, RampsRoadways, Ramps

Emission Factors for Any Calendar Year Between 1952Emission Factors for Any Calendar Year Between 1952--20202020

Varying ConditionsVarying Conditions–– Ambient TemperatureAmbient Temperature–– Travel SpeedTravel Speed–– Operating ModesOperating Modes–– Fuel VolatilityFuel Volatility

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Emissions Models Based on Vehicle Operating ModesEmissions Models Based on Vehicle Operating Modes

MEASUREMEASURE–– Mobile Emissions Assessment System for Urban and Mobile Emissions Assessment System for Urban and

Regional EvaluationRegional Evaluation–– Emission Rate function ofEmission Rate function of

Vehicle SpeedVehicle SpeedAcceleration ProfileAcceleration ProfileIdle TimesIdle TimesPower DemandPower DemandVehicle TechnologyVehicle Technology

–– Fuel Metering RateFuel Metering Rate–– Catalytic Converter TypeCatalytic Converter Type–– Transmission SpeedTransmission Speed

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Emissions Models Based on Microscopic Emissions Models Based on Microscopic Simulation of Traffic FlowSimulation of Traffic Flow

Emission Rates Estimated as a function of instantaneousEmission Rates Estimated as a function of instantaneous ……–– Vehicle Fuel ConsumptionVehicle Fuel Consumption–– SpeedSpeed–– AccelerationAcceleration–– Engine PowerEngine PowerBy Vehicle TypeBy Vehicle Type

TRANSIMS (Transportation Analysis and Simulation TRANSIMS (Transportation Analysis and Simulation Systems)Systems)

INTEGRATIONINTEGRATION

TRAFTRAF--NETSIMNETSIM

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Emissions Models Based on Fuel ConsumptionEmissions Models Based on Fuel Consumption

Emissions Estimated Based on Fuel Emissions Estimated Based on Fuel ConsumptionConsumption

Ex. Ex. SynchroSynchro–– Emissions = Fuel Consumption * Adjustment FactorEmissions = Fuel Consumption * Adjustment Factor–– Adjustment Factor depends on Emission TypeAdjustment Factor depends on Emission Type

Fuel Consumption Estimated as a Function of Fuel Consumption Estimated as a Function of –– VehicleVehicle--milesmiles–– Total Delays in VehicleTotal Delays in Vehicle--Hour / HourHour / Hour–– Total Stops per HourTotal Stops per Hour

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Tools for Emissions Estimation Tools for Emissions Estimation ––A ShortA Short--cut Estimation Method based on Traffic Delaycut Estimation Method based on Traffic Delay

CSCCDCVMCE CSCDVM ++=

XNOor,CO,HCofgmsinchangeE =

VM = change in VMT

CD = change in delay in vehicle-hours (tt at actual speed – tt at free flow speed)

CS = change in number of cold starts

CVM, CCD, and CCS are coefficients

Easy, convenient for emission estimation! See example in text

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Pollutant DispersionPollutant Dispersion

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Factors Affecting Pollutant Dispersion & Factors Affecting Pollutant Dispersion & ConcentrationConcentration

Magnitude of EmissionsMagnitude of EmissionsMeteorological ConditionsMeteorological Conditions–– Wind Speed, Wind Direction, Mixing SpeedWind Speed, Wind Direction, Mixing Speed–– TemperatureTemperature

Topography & Urban Spatial FormTopography & Urban Spatial FormAltitudeAltitudePhysical Mixing, Deposition & Chemical Physical Mixing, Deposition & Chemical ReactionsReactions

Why Concentration is important: harmful effects of pollutants arWhy Concentration is important: harmful effects of pollutants are e measured in terms of their concentrationmeasured in terms of their concentration

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Estimating Pollutant Dispersion & Estimating Pollutant Dispersion & ConcentrationConcentration

Dispersion ModelsDispersion Models–– Box ModelBox Model–– Gaussian Plume ModelGaussian Plume Model–– Numerical ModelNumerical Model

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The Box Model for Predicting Pollutant DispersionThe Box Model for Predicting Pollutant Dispersion

2 2 2a b H+ +

2 2 2a b HV

+ +

Maximum Distance for Transport across the City and out of the Box =

VMaximum Time Taken to be Transported =

2 2 2a b HV

+ +

Average Time Taken to be Transported =

2 2 2

2a b H

V+ +

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The Box Model The Box Model -- AssumptionsAssumptions

Uniform Dispersion of Pollutants in the BoxUniform Dispersion of Pollutants in the Box

Pollutant Concentration as a function of Wind Speed and Pollutant Concentration as a function of Wind Speed and Mixing HeightMixing Height

Increasing Mixing Height or Wind Speed Increases Increasing Mixing Height or Wind Speed Increases Effective Volume in which Pollutants are allowed to mix Effective Volume in which Pollutants are allowed to mix (Higher Wind Speed Implies Lower Pollutant (Higher Wind Speed Implies Lower Pollutant Concentration)Concentration)

Reliability of results depends on a number of assumptionsReliability of results depends on a number of assumptions–– Does not take into account Pollutant DepositionDoes not take into account Pollutant Deposition–– Assumes No Chemical ReactionsAssumes No Chemical Reactions–– Uniform Dispersion in the Box !!Uniform Dispersion in the Box !!

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The Box Model The Box Model –– Example CalculationExample Calculation

3.5 x 2.1 Km city1200 m Average Mixing Height3.5 m/sec. Average Wind Speed(a) Maximum Distance to be Traversed = 4.25 Miles

(b) Maximum Time Taken to be Transported = 4.25 / 3.5 = 1.21 hrs

(c) From (b), all pollutant emissions would have completely dispersed out of the mixing box in 1.21 hours

That is, residual concentration after 1.21 hrs is zero.

Therefore, 2 hrs after release, residual concentration = 0

Thus, if 1,000g of pollutant are released in bursts every two hours, the maximum concentration will simply be:

= 1000 / (volume of the box) = 1000/(3.5*2.1*1.2) = 113.38 g / km3

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The Gaussian Plume Model for Describing DispersionThe Gaussian Plume Model for Describing Dispersion

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The Gaussian Plume ModelThe Gaussian Plume Model

Continuous emission from the sourceContinuous emission from the source

Diffusion in the direction of travel is negligibleDiffusion in the direction of travel is negligible

Increasing size of plume with timeIncreasing size of plume with time

Pollutant concentration follows normal distribution at any Pollutant concentration follows normal distribution at any point in the plumepoint in the plume

Spread of the plume represented by the standard Spread of the plume represented by the standard deviation of the pollutant concentrationdeviation of the pollutant concentration

Moving Away from the source, the maximum Moving Away from the source, the maximum concentration level decreases while the concentration concentration level decreases while the concentration standard deviation increasesstandard deviation increases

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The Gaussian Plume ModelThe Gaussian Plume Model

Calculating ConcentrationCalculating Concentration

1

1 2

2

, ,U L

y y

Gaussian Distribution Functions Corresponding toy yG G Higher and Lower values of and respectivelyσ σ

⎡ ⎤⎢ ⎥= ⎢ ⎥⎢ ⎥⎣ ⎦

Q = Emission Rate of Pollutant in ug/s

U = Average Wind Speed (ft/s)

H = Effective Stack Height = Physical Stack Height (h) + vertical rise of the Plume

Sigmas are the standard Deviation of Pollutant Concentration in the Y and Z directions

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Numerical ModelNumerical Model33--D Grids of conceptual boxes that D Grids of conceptual boxes that occupayoccupay the space the space above a highway corridorabove a highway corridor

Vehicle Emissions Feed the Series of BoxesVehicle Emissions Feed the Series of Boxes

Movement of Pollutant from Box to Box Aided by Movement of Pollutant from Box to Box Aided by Local Wind EffectsLocal Wind Effects

Smaller the Box, More Valid is the Assumption of Smaller the Box, More Valid is the Assumption of Uniform DistributionUniform Distribution

Deposition of Pollutants and Chemical Reactions can Deposition of Pollutants and Chemical Reactions can be Simulated for each Boxbe Simulated for each Box

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Software: Pollutant Dispersion & Concentration Software: Pollutant Dispersion & Concentration EstimationEstimation

HYROAD (HYROAD (HYHYbridbrid ROADROADwayway Model)Model)–– For IntersectionsFor Intersections

–– Concentration: CO, Other Gas Phase Pollutants, Concentration: CO, Other Gas Phase Pollutants, Particulate Matters, Air Toxins etc.Particulate Matters, Air Toxins etc.

–– GUI with Three ModulesGUI with Three ModulesTraffic: Microscopic Traffic Simulation for Speed Traffic: Microscopic Traffic Simulation for Speed Emissions: (With Speed as Input) Emissions: (With Speed as Input)

–– Composite Emission FactorsComposite Emission Factors–– Spatial and Temporal Distribution of EmissionsSpatial and Temporal Distribution of Emissions

DispersionDispersion–– Assuming Assuming LagrangianLagrangian Puff FormationPuff Formation–– Predicts Concentration Near Intersection at Specific DistancesPredicts Concentration Near Intersection at Specific Distances

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Software: Pollutant Dispersion & Concentration Software: Pollutant Dispersion & Concentration EstimationEstimation

CALINECALINE--4 (4 (CACAlifornialifornia LINELINE Source)Source)–– Based on Gaussian Diffusion EquationBased on Gaussian Diffusion Equation–– Pollutant Concentration Predicted at Receptors within Pollutant Concentration Predicted at Receptors within

500 meters of the Roadway500 meters of the Roadway–– InputsInputs

Source Strength (Emissions)Source Strength (Emissions)Meteorology (Meteorology (Temperature, Wind Speed, Direction, Stability)Temperature, Wind Speed, Direction, Stability)Site GeometrySite Geometry

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Framework for Assessing Air Quality ImpactsFramework for Assessing Air Quality Impacts

1. 1 Short-term Effects

(New Traffic Operations Patterns) Higher/lower speeds

Fewer/More Speed Change Events

1.2 Medium-term Effects(New Demand Patterns)

Changes in: Trip Frequency, Trip Mode Trip Route, Trip Schedule, etc.

1.3 Long-term Effects (New Land-use Patterns) Residential (Re)locations

Business(Re)locations1.5 New Emission Rates of Pollutants, U2

Transportation Intervention (Change in System Physical Dimensions or Policy)

1.4 New Travel Amounts and Frequencies, VMT2

Use Dispersion Models to Determine Additional Pollutant

No Transportation Intervention

2.1 Existing or Projected Travel

Amounts and Frequencies, VMT1

2.2 Existing or Emission Rates of

Pollutants, U1

Air Quality “Benefits” = 0.5(U1 – U2)(VMT1 + VMT2)

STEP 3

STEP 1

STEP 2

Add to Existing Concentration to get New Levels of Air Quality

Ascertain whether Overall Pollutant Concentrations violate Air Quality Standards

STEP 4

STEP 5

2.3 Existing Pollutant Concentration

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Software: Pollutant Dispersion & Software: Pollutant Dispersion & Concentration EstimationConcentration Estimation

Other SoftwareOther Software–– ADMSADMS--3 3 –– HIWAYHIWAY–– PALPAL

EPA RecommendedEPA Recommended–– TEXIN 2TEXIN 2–– CALINE 4CALINE 4–– CAL3QHCCAL3QHC

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Monetary Costs of Air PollutionMonetary Costs of Air Pollution

Three Methods for Air Pollution Cost EstimationThree Methods for Air Pollution Cost Estimation

–– Based on Cleaning Air Near Pollutant SourceBased on Cleaning Air Near Pollutant Source

–– Based on Addressing Effects of PollutionBased on Addressing Effects of Pollution

–– Based on WillingnessBased on Willingness--toto--Pay ApproachPay Approach

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Dimensions Dimensions of Air Quality Impacts of Transportation Projects and Policiesof Air Quality Impacts of Transportation Projects and Policies

Impact Type

Temporal Dimension

Spatial Dimension

Air Quality

Econ. Dev.

Land Use

Social

Etc.

Along ROW

Along Corridor

Local

Regional

National

Global

Short-term

Long-termMedium-

term

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Temporal Dimension of AQ ImpactsTemporal Dimension of AQ Impacts

Time Dimension (shortTime Dimension (short--term/longterm/long--term)term)–– ShortShort--term (a few daysterm (a few days--months)months)

–– LongLong--term (many years)term (many years)

Note: Time dimension may also be categorized by Note: Time dimension may also be categorized by -- Impacts during Construction Impacts during Construction -- Impacts after Construction (i.e., during usage/operation Impacts after Construction (i.e., during usage/operation

of the transportation facility)of the transportation facility)

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Spatial Dimension of AQ ImpactsSpatial Dimension of AQ Impacts

–– ROWROW

–– CorridorCorridor

–– Community/Local SystemCommunity/Local System

–– RegionRegion

–– GlobalGlobal

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Local Effects of Transportation Air Pollution

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Regional Effects of Transportation Air Pollution

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Air Quality Standards Air Quality Standards -- NAAQSNAAQS

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Air Quality Impacts in Transportation Systems EvaluationAir Quality Impacts in Transportation Systems Evaluation--Legal BackgroundLegal Background

1955 Air Pollution Control Act1955 Air Pollution Control Act–– First Federal Legislation on Air Pollution ControlFirst Federal Legislation on Air Pollution Control

1963 Clean Air Act (CAA)1963 Clean Air Act (CAA)–– Emission Standards Laid DownEmission Standards Laid Down

1970 CAA Amendments (CAAA)1970 CAA Amendments (CAAA)–– Strong Federal Control in States for Regulating and Reducing Strong Federal Control in States for Regulating and Reducing

EmissionsEmissions–– NAAQS: National Ambient Air Quality Standards for NAAQS: National Ambient Air Quality Standards for Criteria Criteria

Pollutants (Pollutants (NonNon--Attainment Areas)Attainment Areas)–– State Implementation Programs (State Implementation Programs (SIPsSIPs))

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Legal Background (continued)Legal Background (continued)

1970 Federal Aid Highway Act1970 Federal Aid Highway Act–– USDOT and EPA: Issuance of Guidelines Governing Air Quality USDOT and EPA: Issuance of Guidelines Governing Air Quality

Impacts of Highways Impacts of Highways –– Develop Air Quality Improvement MeasuresDevelop Air Quality Improvement Measures

1977 Clean Air Act Amendments (CAAA)1977 Clean Air Act Amendments (CAAA)–– Specific actions to meet Clean Air StandardsSpecific actions to meet Clean Air Standards–– Penalties for Areas that Fail to meet Air Quality StandardsPenalties for Areas that Fail to meet Air Quality Standards

1990 Clean Air Act Amendments (CAAA)1990 Clean Air Act Amendments (CAAA)–– Further Strengthened Conformity RequirementsFurther Strengthened Conformity Requirements–– Justify Project Implementation Based on Emission ModelsJustify Project Implementation Based on Emission Models

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Legal Background (continued)Legal Background (continued)

1991 ISTEA1991 ISTEA–– Intermodal Surface Transportation Efficiency ActIntermodal Surface Transportation Efficiency Act–– Funding Provided for Improving Air QualityFunding Provided for Improving Air Quality

2005 SAFETEA2005 SAFETEA--LULU–– Safe Accountable, Flexible, Efficient Transportation Safe Accountable, Flexible, Efficient Transportation

Equity Act: A Legacy for UsersEquity Act: A Legacy for Users–– Conformity Process ImprovedConformity Process Improved–– Changes in Frequency of Conformity DeterminationsChanges in Frequency of Conformity Determinations

Impacts of Transportation Interventions on Air Quality

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