Activity

Activity can be split into two units, passenger-km and freight-tonne-km. See the equations below (where occupancy is the amount of passengers in a vehicle and load is the weight of the freight in a vehicle):

• Passenger-km = Occupancy * Distance travelled
• Freight-tonne-km = Load * Distance travelled

These are key indicators for the transport sector, given that the 2 major factors in determining any economic sector's energy use is the activity, and the energy intensity of that activity.

Total activity for the whole projection is first estimated using Activity growth. Then once that is done, the activity mix is determined by the distance travelled, occupancy and load:

• Distance travelled (for all cars in the economy) = Mileage * Stocks
  • Stocks: the number of vehicles in the fleet
  • Mileage: the distance travelled by each vehicle
• Occupancy: the number of passengers in each vehicle
• Load: the weight of the freight in each vehicle

And for passenger transport we also use a measure of vehicle ownership to adjust the trend to match our expectations:

• Vehicle ownership: otherwise called stocks per capita and essentially is a measure for passenger vehicles which is heavily affected by the amount of road travel that each member of the population does. If this is low (for example in japan where trains are more popular) then the vehicle ownership (number of vehicles needed) is lower. In the USA this is high. See here for more information on vehicle ownership.

So, for freight Activity Growth is used to create the trend, then we split it into the acitivty mix and are finished. For passenger (road) transport we caculate the trend and then adjust the trend to match our vehicle ownership expectations, and then finally break it down into the activity mix. In the code it's a little more complicated than that but that's the basic idea.

You can read more about activity growth here.

And below you can see a chart of passenger activity:

Notice how there is a bump up in the first two years. This is because of the way we model the effects of COVID. You can read more about that here.

And for freight activity:

These charts are also useful for understanding how the transition to new technologies is going. This is because activity is the best way of understanding how much a vehicle is being used and therefore how much that new technology is being used. However it doesn't take into account the energy intensity of the activity (basically the efficiency of the vehicle being used). This is why, at the end of the day, the best way to understand the effect of a new technology is to look at a breakdown of energy use (e.g. broken down by factor) which will take into account the activity and the intensity. See this page on lmdi methods for breaking down changes in energy use for more information.