Energy III:Methods for Measuring Transport Energy Use

Class #5

I.  How to Measure and Evaluate Energy Use?II. Framework for Analyzing Energy UseIII. Factors Affecting Operating EnergyIV. How to Lie With Statistics

I.  How to measure and evaluate energy use?Answer: Energy input per unit of output

A. What units? Output units? VMT, VKT, pass-miles (PMT), seat-miles, trip, ton-miles of

cargo, ton-mile of capacity, etc. Energy inputs: Btu, joules, kilocalories, kilowatts, gallons, barrels,etc

Btu = energy to raise temp of 1 lb of water 1F 1 Btu = 1055 joules; 1015 Btu = 1 quad

120,000 BTU = 1 gallon gasoline (10% more btu/gallon for diesel)1 bbl = 42 gallon

B. Key Measure: Energy-intensiveness -- energy used per unit of output But how broadly does one measure amount of energy used? Typical measurement of energy used is only energy used for propulsion (easy to compute and understand, based on easily available aggregate data, convenient for comparing vehicles or modes).

Is this a useful or accurate method?

Basic energy components

• Propulsion energy per vehicle-mile• Average number of occupants

• Station and maintenance energy• Construction energy• Vehicle manufacturing energy

• Mode of access• Fraction of trip devoted to access• Circuity

Energyintensive-ness

Line-haul energy

Modal energy

Measures of energy use

Source: Congressional Budget Office, Committee on Environment and Public Works (1977)

Modes

II. Framework for Analyzing Energy Use Sample Breakdowns AirRR Cargo BART Energy Component Measures of Energy Use

39 91 40 Propulsion energy Operating energy (per unit of output (ie, energy Line

eg, ton-mile) intensiveness) haul energy

10 3 16 Terminal & maintenance energy 12 4 44 Guideway construction Modal 5 1 ? Vehicle manufacturing energy Energy ? ? - Energy Used in Access 34 5 ? Circuity (including empty backhauls)

100% 100% 100% Terminology:Direct energy = propulsion energyIndirect energy = construction, maintenance, & operation of guideways and terminals, and construction of vehicles

III. Factors affecting operating energy Gradient (600% difference between –7% and +7% grade) Curvature of road # stops/unit distance (2 stops/mile => 56% more fuel than at steady 40

mph) Load factor (trucks empty 8% of time, rail 40%) Pavement condition: good pavement provides 40% (1 vs 1.7) better fuel

economy than gravel road and 33% better than broken pavements) Speed: at 80mph, vehicles consume ~50% more energy than at 50 mph Temp: 15% more fuel consumed at –20 degrees C than at +20 degrees C Trip length (hot/cold start): ~4 times more energy used (per km) for very

short trip vs longer trip of 30 km. Vehicle characteristics: aerodynamics (air friction), vehicle weight, tire

type (rolling friction), engine, transmission friction, regenerative braking

IV. How to Lie With Statistics

Flaw #1: What about upstream energy use?

Feedstock recovery Fuel recovery Vehicle operation

Analysis on previous slide based only on tank-to-wheels efficiency (ignores upstream well-to-tank energy use)!

Analysis of well-to-wheels energy use (and emissions) is generally referred to as lifecycle analysis (LCA)

When are upstream emissions more important?

The GREET Model (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) is extremely useful for analyzing energy use and GHGs for lifecycle analysis and can be found at:

http://www.transportation.anl.gov/software/GREET/index.html

Petroleum Fuel Pathway

Battery EV Pathway

Greenhouse Gas Emissions per Km, Relative to Gasoline-Powered ICE, Full Energy Cycle

Fuel/Feedstock % ChangeFuel Cells, Hydrogen with Solar Power -90 to –85Ethanol from Wood -90 to –40BEVs, Natural Gas Plants -60 to –25Hybrid EV (Prius) -40 to -30Diesel -25 to -15CNG from NG -20 to 0Methanol from NG -10 to +8BEVs, current U.S. power mix -20 to 0Gasoline -BEVs, new coal plant 0 to +10

Actual impacts could vary considerably. These estimates reflect a large number of assumptions and should be treated as illustrative.

Flaw #2: Energy intensiveness measures are average rates that ignore or simplify differences in:

1. Vehicle characteristics (size, engine, aerodynamics, etc)2. Vehicle loads (car with 1 pass vs 5 pass)3. Operating conditions (speed, pavement, temp, weather)4. Energy required for construction of vehicles, guideways,

terminals, and for maintenance of facilities5. Circuity6. Access energy

Is Transit More Energy Efficient Than Cars?

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Cars

Light Trucks

Bus

Rail Transit

Btu

/pas

seng

er-m

ile

Car

s

Lig

ht T

ruck

s

Bus

Rai

l Tra

nsit

Source: US DOE and ORNL, Transportation Energy Data Book, Edition 26, 2007

These are averages for US. Actual intensities vary dramatically across time of day, routes, and regions (and by trip purpose for cars).

More EI Estimates for Vehicles (US)

0500

100015002000250030003500400045005000

Energy Intensity of U.S. Passenger Travel, 2007

Btu

/Pas

seng

er M

ile

source: Davis, et al, 2009

CO2e Emissions by Mode Per Passenger Mile

NATIONAL AVERAGE* Load Factor

CO2e

(Btu or kWhr per vehicle

mile)

(Btu or kWhr per

passenger mile)

Persons Per Vehicle

(Estimated Pounds CO2e

Per Passenger Mile)

Cars 5,489 3,496 1.57 0.58Personal Trucks 7,447 4,329 1.72 0.71Motorcycles 2,500 2,272 1.1 0.37Vanpool 8,226 1,294 6.4 0.21Transit Bus 38,275 4,318 8.7 0.71Electric Trolley Bus** 5.18 0.39 13.4 0.52Intercity Rail (Amtrak)*** 51,948 2,760 17.9 0.39Light and Heavy Rail Transit*** 70,170 2,750 22.4 0.39Commuter Rail*** 91,525 2,569 32.9 0.36Walking or Biking 0 0 1.0 0.00

REGIONAL EXAMPLE (SEATTLE/PUGET SOUND REGION)

Load Factor

CO2e

Cars (64%) and Personal Trucks (36%) 6,187 4,617 1.34 0.76Sound Transit Buses 33,024 2,517 13.1 0.42King County Metro Diesel and Hybrid Buses 33,024 2,854 11.6 0.47

Energy Intensities

Energy Intensities

Flaw #3: Other associated impacts ignored. Need to determine what is real goal.

How important is energy use analysis?

• Why measure only petroleum?

• More important than carbon emissions?

• What about other benefits and costs?

Other transit benefits??