The figures mentioned in the previous slide refer only to operating energy, and we know from last week’s presentation that that’s only part of the picture. In the transportation system as a whole, we need to consider not just the operating energy intensity of the vehicles we use (First fly-in) but additional considerations as well (second fly-in) . When we include these energy requirements, the picture of total energy consumption per passenger mile looks different. Transportation energy intensities estimated to be: 29% higher for autos 78% higher for dial-a-ride vehicles 84% higher for heavy rail (e.g. BART), and 19% higher for transit buses than operating energy intensities alone (measured in BTUs per passenger-mile)
Energy III:Methods for Measuring Transport Energy Use Class #5I. 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 1°F 1 Btu = 1055 joules; 1015 Btu = 1 quad 120,000 BTU = 1 gallon gasoline (10% more btu/gallon for diesel) 1 bbl = 42 gallonB. 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?
ModesBasic energy components Measures of energy use Energy • Propulsion energy per vehicle-mile intensive- • Average number of occupants ness Line- haul • Station and maintenance energy energy Modal • Construction energy energy • Vehicle manufacturing energy • Mode of access • Fraction of trip devoted to access • Circuity Source: Congressional Budget Office, Committee on Environment and Public Works (1977)
II. Framework for Analyzing Energy Use Sample Breakdowns Air RR 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 energy10 3 16 Terminal & maintenance energy12 4 44 Guideway construction Modal 5 1 ? Vehicle manufacturing energy Energy ? ? - Energy Used in Access34 5 ? Circuity (including empty backhauls)100% 100% 100% Terminology: Direct energy = propulsion energy Indirect 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
Flaw #1: What about upstream energy use?Feedstock recovery Fuel recovery Vehicle operationAnalysis 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
Greenhouse Gas Emissions per Km, Relative to Gasoline- Powered ICE, Full Energy Cycle Fuel/Feedstock % Change Fuel Cells, Hydrogen with Solar Power -90 to –85 Ethanol from Wood -90 to –40 BEVs, Natural Gas Plants -60 to –25 Hybrid EV (Prius) -40 to -30 Diesel -25 to -15 CNG from NG -20 to 0 Methanol from NG -10 to +8 BEVs, current U.S. power mix -20 to 0 Gasoline - 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? 4500 4000 3500Btu/passenger-mile 3000 Cars 2500 Light Trucks Light Trucks Rail Transit 2000 Bus 1500 Rail Transit Cars Bus These are averages for US. 1000 Actual intensities vary 500 dramatically across time of day, routes, and regions 0 (and by trip purpose for cars). Source: US DOE and ORNL, Transportation Energy Data Book, Edition 26, 2007
More EI Estimates for Vehicles (US) Energy Intensity of U.S. Passenger Travel, 2007 5000 Btu/Passenger Mile 4500 4000 3500 3000 2500 2000 1500 1000 500 0 source: Davis, et al, 2009
CO2e Emissions by Mode Per Passenger MileNATIONAL AVERAGE* Energy Intensities Load CO2e Factor (Btu or (Estimated (Btu or kWhr kWhr per Pounds CO2e per vehicle passenger Persons Per Per Passenger mile) mile) Vehicle 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 0.00REGIONAL EXAMPLE Energy Intensities Load CO2e
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??