Comprehensive Transportation Emission Reduction Planning

Many jurisdictions have ambitious greenhouse gas emission reduction targets and are developing plans to achieve them. This column discusses the factors that should be considered in this planning process.

5 minute read

November 17, 2022, 7:00 AM PST

By Todd Litman

View of cars in traffic from behind with visible tailpipe emissions

NadyGinzburg / Tailpipe emissions

Many jurisdictions have ambitious greenhouse gas emission reduction targets and are developing plans to achieve them. Since transportation is one of the largest emission sources, it is a major component of these plans.

There are many possible ways to reduce transportation emissions. These include clean vehicle strategies that reduce emission rates per vehicle mile, and transportation demand management (TDM) and Smart Growth policies that reduce total vehicle travel, as summarized below.

Types of Emission Reduction Strategies

Clean Vehicles	Vehicle Travel Reductions
Technologies and policies that reduce emission rates per vehicle-mile	TDM and Smart Growth policies that reduce total vehicle travel
Shifts to more efficient and alternative fuel vehicles (e.g., hybrid, electric and hydrogen). High emitting vehicle scrapage programs. Efficient driving and anti-idling campaigns. Switching to lower carbon and cleaner fuels. Inspection and maintenance programs. Resurface highways. Roadside “high emitter” identification. Higher fuel prices.	Multimodal planning (improve walking, bicycling, public transit, ridesharing, etc.) Transportation Demand Management programs (commute trip reduction, freight transport management, etc.). Efficient road, parking and vehicle pricing. Smart Growth policies that create more compact and multimodal communities. Parking policy reforms. Higher fuel prices.

Clean vehicle strategies reduce per-mile emission rates. Vehicle travel reduction strategies reduce total vehicle mileage.

Which strategies are most effective and beneficial overall? That depends on how they are analyzed, including the scope of impacts considered and the methods used to predict those impacts. My new report, Comprehensive Transportation Emission Reduction Planning: Guidelines for Evaluating Transportation Emission Reduction Strategies, explores these issues. It identifies ten factors that should be considered when evaluating and prioritizing potential transportation emission reduction strategies, as summarized in the table below.

Factors to Consider in Emission Reduction Evaluation

Factor	Description	Methods	Effect if Ignored
Embodied emissions	Emissions from vehicles, batteries, fuel and infrastructure production.	Apply lifecycle analysis that accounts for all emissions.	Exaggerates clean vehicles emission reductions.
Rebound effects	Additional vehicle travel and size caused by reduced operating costs, and the increased external costs that result.	Account for rebound effects and the additional external costs that result.	Exaggerates clean vehicles emission reductions and benefits.
Implementation costs and subsidies	Consider all costs of developing, producing and operating clean vehicles and their infrastructure.	Consider all costs when evaluating and comparing strategies.	Tends to underestimate clean vehicle total costs.
Realistic fleet penetration predictions	The time needed for clean vehicles to penetrate vehicle fleets and travel.	Use realistic fleet and travel predictions.	Optimistic predictions exaggerate clean vehicle emission reductions.
Leverage and synergistic effects	Additional vehicle travel reductions provided by integrated TDM and Smart Growth programs.	Consider leverage and synergistic effects in modelling and analysis.	Undervalues integrated TDM and Smart Growth programs.
Comprehensive vehicle travel reduction strategies	The variety of TDM and Smart Growth strategies considered in analysis.	Consider all potentially effective TDM and Smart Growth strategies.	Overlooking cost effective TDM strategies undervalues vehicle travel reduction solutions.
Indirect costs and co-benefits	The range of impacts considered in the analysis, including indirect costs and co-benefits.	Account for all significant impacts, including indirect and long term effects.	Overlooking these impacts tends to undervalue vehicle travel reduction strategies.
Cost efficiency	Comparison of unit costs, such as dollars per tonne of emissions reduced.	Compare total unit costs between strategies.	Favors clean vehicles over vehicle travel reductions.
Latent demand for multimodal lifestyles	The portion of travellers who want to rely more on non-auto modes and live in more multimodal communities.	Consider growing consumer demands for non-auto travel and walkable communities.	Ignoring this factor undervalues TDM and Smart Growth strategies.
State-of-Art models	The quality of models used to predict travel and emission impacts.	Use up-to-date integrated models.	Outdated models tend to undervalue vehicle travel reduction strategies.

These factors should be considered when evaluating transportation emission reduction strategies. Failing to account for them tends to bias emission reduction planning.

As part of this study I reviewed more than two dozen emission reduction plans. I found that most plans are biased in ways that favor clean vehicle subsidies over vehicle travel reduction strategies. For example, few account for embodied emissions, rebound effects, TDM and Smart Growth co-benefits, or the very long time period required for clean vehicles to penetrate the fleet. Many plans assume that clean vehicle strategies are more effective, cost effective, fast, reliable, and popular than vehicle travel reductions. My research challenges those assumptions.

This is not to suggest that clean vehicle strategies are bad and should be rejected. However, this research indicates that their emission reductions are often smaller than predicted. Considering embodied energy, clean vehicles typically reduce per-mile emission rates by half to three quarters, and their annual emission reductions are even smaller due to induced vehicle travel which increases their emissions and external costs. In fact, a large electric SUV or light truck has total emissions comparable to a small gasoline car. As a result, it is an exaggeration to call electric or hydrogen vehicles “zero emissions;” it is more accurate to call them “lower-emission” and “elsewhere-emission” vehicles.

Lifecycle Emissions

Clean vehicles have relatively high unit costs per tonne of emissions reduced, and require significant subsidies. On the other hand, vehicle travel reduction strategies often provide additional, but often overlooked benefits and respond to latent consumer demands for non-auto travel, and tend to be very cost effective.

In 2021, hybrid and electric vehicles represented about 3% of new vehicle sales, and these are mainly cars due to slower development of electric SUVs, light truck and vans. Optimistically, half of new vehicles could be electric by 2030 but realistically it will take longer, and the remaining fossil fuel vehicles will skew to low fuel economy. With current policies, the fleet is unlikely to be fully electric by 2050, as illustrated below.

Optimistic and Realistic Electric Vehicle Sales and Fleet Penetration (www.vtpi.org/cterp.pdf) — Optimistically, half of new vehicle sales could be electric by 2030, but realistically it will probably take longer, and since only about 6% of vehicles are replaced each year, it takes 15-20 years before a percentage of vehicle sales are reflected in the fleet. With current policies it is unlikely that the fleet will be fully electric before 2050.

Many TDM strategies can be implemented quickly, reducing emissions far faster than clean vehicle implementation. An integrated set of TDM and Smart Growth strategies can reduce transportation emissions by 20-50 percent in ways that are cost-effective and beneficial overall, considering all impacts.

The figure below indicates predicted emission reductions that can be achieved by clean vehicles and vehicle travel reductions.

Comparing Emission Reductions

This analysis suggests that to be efficient and equitable transportation emission reduction plans should rely at least as much on vehicle travel reductions as on clean vehicle strategies, with particular emphasis on “quick win” strategies that can be implemented in a few years.

There is a positive message here. With better analysis we can identify true win-win emission reduction strategies that also help achieve other economic, social and environmental goals.

Energy Environment Transportation Emissions Greenhouse Gas Emissions Climate Change Emissions Reductions Tailpipe Emissions View More

Todd Litman

Todd Litman is founder and executive director of the Victoria Transport Policy Institute, an independent research organization dedicated to developing innovative solutions to transport problems. His work helps to expand the range of impacts and options considered in transportation decision-making, improve evaluation methods, and make specialized technical concepts accessible to a larger audience. His research is used worldwide in transport planning and policy analysis.

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I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

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