A Handy Framework for Evaluating the Next Sustainable Mobility Pitch

What can the Kaya Identity teach us about urban transportation?

• Reminder that you can find my transport decarbonization news roundup at the bottom of this email

A Handy Framework for Evaluating the Next Sustainable Mobility Pitch

If you’ve never heard of the Kaya Identity, it’s worth getting to know. It’s a simple equation for understanding the drivers of CO2 emissions:

F is total annual emissions, P is population, G/P is annual GDP per person, E/G is energy consumed per unit of GDP, and F/E is the CO2 intensity of energy production. CO2 emissions can be driven up (or down) by a rise (or decline) in any of those variables. Growing population, all else equal, drives up emissions. Decreasing the energy required for a unit of GDP, for example by an economy shifting from manufacturing to services, tends to lower emissions. 

To see the Kaya Identity in action, you can check out this summary of emissions in the United States for the last 30 years.

Most strategies to reduce emissions focus on that last F/E variable, lowering the CO2 intensity of energy by shifting from fossil fuels to renewables. Some other strategies that might lower emissions tend to be considered off limits. We might be able to cut emissions by lowering G/P (GDP per capita), sometimes referred to as ‘degrowth’, but that view tends to be confined to the fringes of the climate conversation. 

I raise the Kaya Identity because it provides a useful way to think about the transport decarbonization problem. You can construct a similar equation for urban transport emissions:

As before, emissions can rise (or fall) with an increase (or decrease) in any of these variables. More population, more travel, or more energy intensive modes of travel (like a large SUV driven alone) can all drive emissions up. You can also think of all the common solutions for reducing urban transport emissions as addressing one (or more) pieces of this equation: limiting travel; encouraging biking, walking, and public transit; or converting vehicles to electric drive. The popular avoid-shift-improve framework is built on this understanding.

Below, I’ve connected some of the popular emissions reduction strategies to the variable they address.

You can analyze any proposed solution to the transportation emissions problem through this lens. How might it drive these factors up (or down)? 

Advocates for flying cars have claimed that they’re sustainable because they use less energy per passenger mile of travel. Even if that were true, it ignores that making travel faster - as flying vehicles would, assuming they were successful - drives the ‘travel miles per person’ variable up, neutralizing any gains. 

Next time someone approaches you with the latest solution for transport decarbonization, you can pull this framework out of your back pocket.

New & Worth a Read

• The International Energy Agency (IEA) released their annual energy outlook [overview, exec summary]. As a transport person learning about energy, I’ve found this a helpful high level summary of where the world stands.

• Waymo really, finally, actually launches a driverless taxi. I was in Silicon Valley for the 2014-2017 peak of the autonomous vehicle hype cycle (Lyft was going to have 50% of their rides in autonomous vehicles this year!) so I’m generally a skeptic on AV deployment. But smart people seem to think that this Waymo announcement is real. From a  decarbonization perspective, AVs are likely a mixed bag. Evidence suggests they would induce more travel but might make it easier to electrify vehicles.

• The MPO in the San Francisco Bay Area promoted a policy to push 60% of employees to work remotely, ostensibly on climate grounds. It’s not actually clear if telecommuting reduces emissions, so this seems, at best, questionable.  

• Hydrogen is having a(nother) moment. Great conversation on the topic here, with potential applications as a transportation fuel covered starting at 17:10. More background here. Always good to read what Michael Liebrich has to say.

• An ITF study makes a lot of modes of ‘new mobility’ look … not great. Related: from a lifecycle perspective, free floating e-scooters increased emissions in Paris. [link] Also, an update on Chinese bikeshare graveyards.

• Norway, which has a goal of all new cars being electric by 2025, hit a new milestone as 60% of new car sales were electric or plug-in hybrids in September. [link] The UK is making quick progress, too. Though, of course, electrification of the light-duty vehicle fleet alone will not meet mitigation targets, at least in the US.

• If you want to get to 0 emission transport, you can’t leave out lawnmowers and forklifts.

• Thoughtful thread in reply to last week’s post on Boston’s zero carbon plans.

Till next time,

Andrew