My posting of October 29th examined two of the ways we risk under-counting the greenhouse gas emissions (GHGs) from favored energy technologies such as biofuels and electric vehicles, with potentially serious consequences. Well, it turns out that the same joint proposal by the EPA and Department of Transportation establishing new fuel economy and vehicle emissions rules incorporates another, subtler distortion that could be even more significant over the next few years than treating electric vehicles (EVs) as if their external power sources emitted no GHGs. Consider the many ways in which personal transportation in the US has changed since the mid-1970s--longer commutes, heavier traffic, and new vehicle technologies--and then ask how it could possibly make sense to embed a vehicle-use statistic set by a 1970s' law at the heart of the new Corporate Average Fuel Economy system. Yet that is precisely what these new rules would do.
My scrutiny of the draft "Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards" rulemaking was an outgrowth of a recent conversation with Jeff Breneman, Executive Director of the US Coalition for Advanced Diesel Cars. In addition to promoting to an American audience the benefits of the improved engine technologies that have enabled diesel passenger cars to capture over half of the new-car market in Europe, this group advocates an approach to emissions reduction and improved energy security that emphasizes outcomes, rather than "flavor of the month" pathways. That resonates with themes I've been expounding since I began this blog nearly seven years ago.
According to Mr. Breneman, achieving a level playing field for advanced vehicle types such as diesels, hybrids, plug-in hybrids and pure EVs depends on establishing metrics for judging them that reflect "real-world driving." In the case of the draft EPA/NHTSA rules, that means updating their assumption that the average American drives 55% in city traffic and 45% on the highway. That ratio was set by the Energy Policy and Conservation Act of 1975, when there were 100 million fewer cars on our roads, each driving on average about 2,000 fewer miles per year, and the only alternative fuel vehicle I was aware of burned propane. According to the EPA's own data from 2006, current average driving patterns exhibit a roughly 43% city, 57% highway split, even though its 2010 vehicle sticker program is still based on the old 55/45 ratio.
This divergence between current and historical driving patterns has become more significant as the array of available vehicle choices has broadened to encompass technologies such as hybrids that perform best in city driving, but offer little highway benefit, and others such as diesels that are at their best in sustained driving above 45 miles per hour (highway driving by definition in the EPA's split.) For example, the 2010 VW Jetta Diesel is rated at 30 mpg city/42 mpg highway, compared to 41/36 for the Ford Fusion Hybrid.
The two agencies involved indicate they intend to assess carmakers' fleets using the old split until at least 2017. That means that during this crucial transition to stricter fuel economy standards these rules will motivate manufacturers to invest more in vehicle technologies that perform best under the old assumptions--despite the resulting misalignment with how consumers really drive now--in order to meet their tougher corporate targets. The difference gives hybrids an extra edge vs. diesel, over and above any disparity in purchaser tax credits. It would likely limit the choices available to consumers, given the high costs of developing additional models with drastically different powertrains.
Prolonged reliance on the outdated 55/45 split could affect actual GHG emissions, as well. A study by the Energy Information Agency earlier this year indicated that the lifecycle emissions of diesel vehicles are typically 15% less than for comparable gasoline-powered vehicles. When fueled with blends containing 20% biodiesel they emit levels of CO2 per mile similar to gasoline hybrids or plug-in hybrids recharged using grid-average power in much of the US. That's a surprising result for a technology option that generally costs somewhat less than hybridization and many thousands of dollars less per car than a plug-in with its expensive batteries.
I don't know whether US consumers would ever warm up to diesels to the extent that Europeans have. But given their attractive fuel economy and emissions benefits, they shouldn't be impeded from trying, merely because of an accounting ratio that was set when I was driving my first car. Nor do I buy the argument that diesels are a dead end, compared to electric vehicles. Interpolating from the EIA data cited above, diesel cars running on advanced biofuel derived from sources that don't compete with food crops or result in deforestation appear no less sustainable than a plug-in hybrid backed by California's low-emission power grid. When the time comes for me to buy my next car, I hope to see a wider array of clean diesel options, including some from GM and Ford, which make wonderful diesel cars in Europe.