Module: BrighterPlanet::RailTrip::CarbonModel

Defined in:
lib/rail_trip/carbon_model.rb

Overview

Rail trip: carbon model This module is used by [Brighter Planet](brighterplanet.com)‘s [emission estimate service](carbon.brighterplanet.com) to provide greenhouse gas emission estimates for rail trips.

For more information see:

* [API documentation](http://carbon.brighterplanet.com/rail_trips/options)
* [Source code](http://github.com/brighterplanet/rail_trip)

Collaboration Contributions to this carbon 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 shold include test coverage for new functionality. Please see [sniff](github.com/brighterplanet/sniff#readme), our emitter testing framework, for more information.

Class Method Summary collapse

Class Method Details

.included(base) ⇒ Object 



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# File 'lib/rail_trip/carbon_model.rb', line 27

def self.included(base)
  ##### The carbon model
  
  # This `decide` block encapsulates the carbon model. The carbon model is
  # executed with a set of "characteristics" as input. These characteristics are
  # parsed from input received by the client request according to the
  # [characterization](characterization.html).
  base.decide :emission, :with => :characteristics do

    # The emission committee returns a carbon emission estimate in kilograms CO2e.
    committee :emission do # returns kg CO2

      # This calculation technique transforms amounts of diesel and electricity
      # consumed during the rail trip---via their current emission factors---to
      # an overall emission value. This value is divided by the passenger count
      # to obtain a per-passenger emission share.  
      quorum 'from fuel and passengers', :needs => [:diesel_consumed, :electricity_used, :passengers] do |characteristics|
        #((       litres diesel         ) * (  kilograms CO2 / litre diesel   ) + (           kwH                  ) * (     kilograms CO2 / kWh               ))
        (characteristics[:diesel_consumed] * base.research(:diesel_emission_factor) + characteristics[:electricity_used] * RailTrip.rail_trip_model.research(:electricity_emission_factor)) / characteristics[:passengers]
      end
    end
    
    # Generally the client will not know the exact amount of diesel consumed
    # during the rail trip, so it must be calculated.
    committee :diesel_consumed do # returns litres diesel
      
      # This technique uses trip distance and fuel efficiency to determine diesel
      # consumption.
      quorum 'from distance and diesel intensity', :needs => [:distance, :diesel_intensity] do |characteristics|
        #(          kilometres        ) * (     litres diesel / kilometre      )
        characteristics[:distance] * characteristics[:diesel_intensity]
      end
    end
    
    # Similarly, electricity consumption will typically be computed here.
    committee :electricity_used do # returns kWh

      # As with diesel consumption, we calculate electricity use by multiplying
      # distance by "electric intensity"--- an analogue of fuel efficiency.
      quorum 'from distance and electricity intensity', :needs => [:distance, :electricity_intensity] do |characteristics|
        #(       kilometres           ) * (         kWh / kilometre                  )
        characteristics[:distance] * characteristics[:electricity_intensity]
      end
    end
    
    # The distance of the rail trip is necessary to perform each of the above
    # calculations and can be calculated using several methods.
    committee :distance do # returns kilometres
      
      # The primary distance-calculation method is directly accepting an estimate from
      # the client.
      quorum 'from distance estimate', :needs => :distance_estimate do |characteristics|
        characteristics[:distance_estimate]
      end
      
      # Alternatively we can calculate distance by combining an estimate of trip
      # duration with the train's average speed.
      quorum 'from duration', :needs => [:duration, :speed] do |characteristics|
        #(       hours           ) * (        kph          )
        characteristics[:duration] * characteristics[:speed]
      end
      
      # Finally, we can assume the trip covered an average distance, scoped by
      # its rail class (subway vs. intercity, for example).
      quorum 'from rail class', :needs => :rail_class do |characteristics|
        characteristics[:rail_class].distance
      end
    end
    
    # Diesel intensity is analogous to fuel efficiency (mpg), but are expressed
    # in units of fuel per unit of distance.
    committee :diesel_intensity do # returns litres diesel / vehicle kilometre
      
      # Brighter Planet has pre-calculated intensities for popular rail classes.
      quorum 'from rail class', :needs => :rail_class do |characteristics|
        characteristics[:rail_class].diesel_intensity
      end
    end
    
    # Electricity intensity describes the amount of electric power consumed per
    # unit of train travel distance.
    committee :electricity_intensity do # returns kWh / vehicle kilometre
      
      # Again, intensities have been pre-calculated for popular rail classes.
      quorum 'from rail class', :needs => :rail_class do |characteristics|
        characteristics[:rail_class].electricity_intensity
      end
    end
    
    # Speed is only necessary when used in combination with trip (temporal)
    # duration to determine distance.
    committee :speed do # returns kph
      
      # Rail classes provide average speed.
      quorum 'from rail class', :needs => :rail_class do |characteristics|
        characteristics[:rail_class].speed
      end
    end
    
    # Each passenger is responsible for a share of the train trip's total
    # footprint.
    committee :passengers do
      
      # A passenger count can be gleaned from popular rail classes.
      quorum 'from rail class', :needs => :rail_class do |characteristics|
        characteristics[:rail_class].passengers
      end
    end
    
    # The vehicle used for a rail trip can be meaningfully assigned to one
    # of a list of categories called classes, including subways, intercity
    # rail, and commuter rail, for example.
    committee :rail_class do
      
      # If the client does not provide a rail class, we use an artificial
      # rail class, constructed using a weighted average approach.
      quorum 'default' do
        RailClass.fallback
      end
    end
  end
end