impact_model.rb

Copyright © 2010 Brighter Planet. See LICENSE for details. Contact Brighter Planet for dual-license arrangements.

 

      		
    

    

      
        

          
        

        
Bus trip impact model



This model is used by the Brighter Planet CM1 web service to calculate the per-passenger impacts of a bus trip, such as energy use and greenhouse gas emissions.

      		
      
        

      		
    

    

      
        

          
        

        
Timeframe



The model calculates impacts that occured during a particular time period (timeframe).
For example if the timeframe is February 2010, a trip that occurred (date) on February 15, 2010 will have impacts, but a trip that occurred on January 31, 2010 will have zero impacts.



The default timeframe is the current calendar year.

      		
      
        

      		
    

    

      
        

          
        

        
Calculations



The final impacts are the result of the calculations below. These are performed in reverse order, starting with the last calculation listed and finishing with the greenhouse gas emissions calculation.



Each calculation listing shows:



    

  • value returned (units of measurement)
    • 

  • description of the value
    • 

  • calculation methods, listed from most to least preferred
    • 





Some methods use values returned by prior calculations. If any of these values are unknown the method is skipped.
If all the methods for a calculation are skipped, the value the calculation would return is unknown.

      		
      
        

      		
    

    

      
        

          
        

        
Standard compliance



When compliance with a particular standard is requested, all methods that do not comply with that standard are ignored.
Thus any values a method needs will have been calculated using a compliant method or will be unknown.
To see which standards a method complies with, look at the :complies => section of the code in the right column.



Client input complies with all standards.

      		
      
        

      		
    

    

      
        

          
        

        
Collaboration



Contributions to this impact model are actively encouraged and warmly welcomed. This library includes a comprehensive test suite to ensure that your changes do not cause regressions. All changes should include test coverage for new functionality. Please see sniff, our emitter testing framework, for more information.

      		
      
        
module BrighterPlanet
  module BusTrip
    module ImpactModel
      def self.included(base)
        base.decide :impact, :with => :characteristics do

      		
    

    

      
        

          
        

        

      		
      
        
          

      		
    

    

      
        

          
        

        
Carbon (kg CO2e)



One passenger’s share of the trip’s anthropogenic greenhouse gas emissions during timeframe.

      		
      
        
          committee :carbon do

      		
    

    

      
        

          
        

        
Sum co2 emission (kg), ch4 emission (kg CO2e), n2o emission (kg CO2e), and hfc emission (kg CO2e) to give kg CO2e.

      		
      
        
            quorum 'from co2 emission, ch4 emission, n2o emission, and hfc emission', :needs => [:co2_emission, :ch4_emission, :n2o_emission, :hfc_emission],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
              characteristics[:co2_emission] + characteristics[:ch4_emission] + characteristics[:n2o_emission] + characteristics[:hfc_emission]
            end
          end
          

      		
    

    

      
        

          
        

        
CO2 emission (kg)



One passenger’s share of the trip’s CO2 emissions from anthropogenic sources during timeframe.

      		
      
        
          committee :co2_emission do

      		
    

    

      
        

          
        

        
Multiply each fuel use (l) by the fuel’s co2 emission factor (kg / l) to give co2 emissions from each fuel (kg).
Sum the fuel co2 emissions to give kg.

      		
      
        
            quorum 'from fuel uses', :needs => :fuel_uses,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:fuel_uses][:gasoline]  * BusFuel.find_by_name("Gasoline").co2_emission_factor +
                characteristics[:fuel_uses][:diesel]    * BusFuel.find_by_name("Diesel").co2_emission_factor +
                characteristics[:fuel_uses][:cng]       * BusFuel.find_by_name("CNG").co2_emission_factor +
                characteristics[:fuel_uses][:lng]       * BusFuel.find_by_name("LNG").co2_emission_factor +
                characteristics[:fuel_uses][:lpg]       * BusFuel.find_by_name("LPG").co2_emission_factor +
                characteristics[:fuel_uses][:methanol]  * BusFuel.find_by_name("Methanol").co2_emission_factor +
                characteristics[:fuel_uses][:biodiesel] * BusFuel.find_by_name("Biodiesel").co2_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
CO2 biogenic emission (kg)



One passenger’s share of the trip’s CO2 emissions from biogenic sources during timeframe.

      		
      
        
          committee :co2_biogenic_emission do

      		
    

    

      
        

          
        

        
Multiply each fuel use (l) by the fuel’s co2 biogenic emission factor (kg / l) to give co2 biogenic emissions from each fuel (kg).
Sum the fuel co2 biogenic emissions to give kg.

      		
      
        
            quorum 'from fuel uses', :needs => :fuel_uses,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:fuel_uses][:gasoline]  * BusFuel.find_by_name("Gasoline").co2_biogenic_emission_factor +
                characteristics[:fuel_uses][:diesel]    * BusFuel.find_by_name("Diesel").co2_biogenic_emission_factor +
                characteristics[:fuel_uses][:cng]       * BusFuel.find_by_name("CNG").co2_biogenic_emission_factor +
                characteristics[:fuel_uses][:lng]       * BusFuel.find_by_name("LNG").co2_biogenic_emission_factor +
                characteristics[:fuel_uses][:lpg]       * BusFuel.find_by_name("LPG").co2_biogenic_emission_factor +
                characteristics[:fuel_uses][:methanol]  * BusFuel.find_by_name("Methanol").co2_biogenic_emission_factor +
                characteristics[:fuel_uses][:biodiesel] * BusFuel.find_by_name("Biodiesel").co2_biogenic_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
CH4 emission (kg CO2e)



One passenger’s share of the trip’s CH4 emissions during timeframe.

      		
      
        
          committee :ch4_emission do

      		
    

    

      
        

          
        

        
Sum the fuel uses (l) to give total fuel use (l).
Divide each fuel use (l) by total fuel use (l) and multiply by distance per passenger (km) to give the distance attributed to each fuel (km).
Multiply the distance attributed to each fuel (km) by the fuel’s ch4 emission factor (kg CO2e / km) to give ch4 emissions from each fuel (kg CO2e).
Sum the fuel ch4 emissions to give kg CO2e.

      		
      
        
            quorum 'from distance per passenger and fuel uses', :needs => [:distance_per_passenger, :fuel_uses],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                total_fuel = characteristics[:fuel_uses].values.inject(:+)
                
                if total_fuel > 0
                  characteristics[:fuel_uses][:gasoline]  / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Gasoline").ch4_emission_factor +
                  characteristics[:fuel_uses][:diesel]    / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Diesel").ch4_emission_factor +
                  characteristics[:fuel_uses][:cng]       / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("CNG").ch4_emission_factor +
                  characteristics[:fuel_uses][:lng]       / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("LNG").ch4_emission_factor +
                  characteristics[:fuel_uses][:lpg]       / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("LPG").ch4_emission_factor +
                  characteristics[:fuel_uses][:methanol]  / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Methanol").ch4_emission_factor +
                  characteristics[:fuel_uses][:biodiesel] / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Biodiesel").ch4_emission_factor
                else
                  0
                end
            end
          end
          

      		
    

    

      
        

          
        

        
N2O emission (kg CO2e)



One passenger’s share of the trip’s N2O emissions during timeframe.

      		
      
        
          committee :n2o_emission do

      		
    

    

      
        

          
        

        
Sum the fuel uses (l) to give total fuel use (l).
Divide each fuel use (l) by total fuel use (l) and multiply by distance per passenger (km) to give the distance attributed to each fuel (km).
Multiply the distance attributed to each fuel (km) by the fuel’s n2o emission factor (kg CO2e / km) to give n2o emissions from each fuel (kg CO2e).
Sum the fuel n2o emissions to give kg CO2e.

      		
      
        
            quorum 'from distance per passenger and fuel uses', :needs => [:distance_per_passenger, :fuel_uses],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                total_fuel = characteristics[:fuel_uses].values.inject(:+)
                
                if total_fuel > 0
                  characteristics[:fuel_uses][:gasoline]  / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Gasoline").n2o_emission_factor +
                  characteristics[:fuel_uses][:diesel]    / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Diesel").n2o_emission_factor +
                  characteristics[:fuel_uses][:cng]       / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("CNG").n2o_emission_factor +
                  characteristics[:fuel_uses][:lng]       / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("LNG").n2o_emission_factor +
                  characteristics[:fuel_uses][:lpg]       / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("LPG").n2o_emission_factor +
                  characteristics[:fuel_uses][:methanol]  / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Methanol").n2o_emission_factor +
                  characteristics[:fuel_uses][:biodiesel] / total_fuel * characteristics[:distance_per_passenger] * BusFuel.find_by_name("Biodiesel").n2o_emission_factor
                else
                  0
                end
            end
          end
          

      		
    

    

      
        

          
        

        
HFC emission (kg CO2e)



One passenger’s share of the trip’s HFC emissions during timeframe.

      		
      
        
          committee :hfc_emission do

      		
    

    

      
        

          
        

        
Multiply distance per passenger (km) by the bus class air conditioning emission factor (kg CO2e / km) to give kg CO2e.

      		
      
        
            quorum 'from distance per passenger and bus class', :needs => [:distance_per_passenger, :bus_class],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:distance_per_passenger] * characteristics[:bus_class].air_conditioning_emission_factor
            end
          end
          
=begin

      		
    

    

      
        

          
        

        
Energy (MJ)



One passenger’s share of the trip’s energy use during timeframe.

      		
      
        
          committee :energy do

      		
    

    

      
        

          
        

        
Multiply each fuel use (l) by the fuel’s energy content (MJ / l) to give energy for each fuel (MJ).
Sum the fuel energies to give MJ.

      		
      
        
            quorum 'from fuel uses', :needs => :fuel_uses do |characteristics|
              characteristics[:fuel_uses][:gasoline]  * BusFuel.find_by_name("Gasoline").energy_content +
              characteristics[:fuel_uses][:diesel]    * BusFuel.find_by_name("Diesel").energy_content +
              characteristics[:fuel_uses][:cng]       * BusFuel.find_by_name("CNG").energy_content +
              characteristics[:fuel_uses][:lng]       * BusFuel.find_by_name("LNG").energy_content +
              characteristics[:fuel_uses][:lpg]       * BusFuel.find_by_name("LPG").energy_content +
              characteristics[:fuel_uses][:methanol]  * BusFuel.find_by_name("Methanol").energy_content +
              characteristics[:fuel_uses][:biodiesel] * BusFuel.find_by_name("Biodiesel").energy_content
            end
          end
=end

=begin
  NOTE: electricity use is negligible (contributes about 0.001% of total emissions)
=end
          

      		
    

    

      
        

          
        

        
Fuel uses (l)



One passenger’s share of the trip’s use of each of a variety of bus fuels during timeframe.

      		
      
        
          committee :fuel_uses do

      		
    

    

      
        

          
        

        
For each fuel, multiply distance per passenger (km) by the bus class fuel intensity for the fuel (l / km) to give l.

      		
      
        
            quorum 'from distance per passenger and bus class', :needs => [:distance_per_passenger, :bus_class],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                {
                  :gasoline  => (characteristics[:distance_per_passenger] * characteristics[:bus_class].gasoline_intensity),
                  :diesel    => (characteristics[:distance_per_passenger] * characteristics[:bus_class].diesel_intensity),
                  :cng       => (characteristics[:distance_per_passenger] * characteristics[:bus_class].cng_intensity),
                  :lng       => (characteristics[:distance_per_passenger] * characteristics[:bus_class].lng_intensity),
                  :lpg       => (characteristics[:distance_per_passenger] * characteristics[:bus_class].lpg_intensity),
                  :methanol  => (characteristics[:distance_per_passenger] * characteristics[:bus_class].methanol_intensity),
                  :biodiesel => (characteristics[:distance_per_passenger] * characteristics[:bus_class].biodiesel_intensity)
                }
            end
          end
          

      		
    

    

      
        

          
        

        
Distance per passenger (km)



The distance traveled per passenger during timeframe.

      		
      
        
          committee :distance_per_passenger do

      		
    

    

      
        

          
        

        
If date falls within timeframe, divide distance (km) by passengers to give km.
Otherwise distance per passenger is zero.

      		
      
        
            quorum 'from distance, passengers, date, and timeframe', :needs => [:distance, :passengers, :date],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics, timeframe|
=begin
  FIXME TODO date should already be coerced
=end
                date = characteristics[:date].is_a?(Date) ? characteristics[:date] : Date.parse(characteristics[:date].to_s)
                timeframe.include?(date) ? characteristics[:distance] / characteristics[:passengers] : 0
            end
          end
          

      		
    

    

      
        

          
        

        
Distance (km)



The trip’s distance.

      		
      
        
          committee :distance do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise divide duration (seconds) by 3600 (seconds / hour) and multiply by speed (km / hour) to give km.

      		
      
        
            quorum 'from duration and speed', :needs => [:duration, :speed],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:duration] / 3600.0 * characteristics[:speed]
            end
            

      		
    

    

      
        

          
        

        
Otherwise use the bus class average trip distance (km).

      		
      
        
            quorum 'from bus class', :needs => :bus_class do |characteristics|
              characteristics[:bus_class].distance
            end
          end
          

      		
    

    

      
        

          
        

        
Speed (km / hour)



The trip’s average speed.

      		
      
        
          committee :speed do

      		
    

    

      
        

          
        

        
Use the bus class average speed (km / hour).

      		
      
        
            quorum 'from bus class', :needs => :bus_class,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:bus_class].speed
            end
          end
          

      		
    

    

      
        

          
        

        
Duration (seconds)



The trip’s duration.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Passengers



The number of passengers on the bus.

      		
      
        
          committee :passengers do

      		
    

    

      
        

          
        

        
Use the bus class average number of passengers.

      		
      
        
            quorum 'from bus class', :needs => :bus_class,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:bus_class].passengers
            end
          end
          

      		
    

    

      
        

          
        

        
Bus class



The type of bus used.

      		
      
        
          committee :bus_class do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use an artificial bus class that represents US averages.

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do
                BusClass.fallback
            end
          end
          

      		
    

    

      
        

          
        

        
Date (date)



The day the trip occurred.

      		
      
        
          committee :date do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use the first day of timeframe.


      		
      
        
            quorum 'from timeframe',
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics, timeframe|
                timeframe.from
            end
          end
        end
      end
    end
  end
end