Driving takes its toll: Emissions database

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  • Published: Apr 15, 2015
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
thumbnail image: Driving takes its toll: Emissions database

Vehicular emissions

Vehicles generate about 28 percent of carbon dioxide emissions from fossil fuels in the USA, a proportion that is rising in many urban areas. Now, researchers have created DARTE (Database of Road Transportation Emissions), a new US wide data inventory to allow more detailed emission studies to be carried out in the context of climate change and other pollution effects.

Vehicles generate about 28 percent of carbon dioxide emissions from fossil fuels in the USA, a proportion that is rising in many urban areas. Now, researchers have created DARTE (Database of Road Transportation Emissions), a new US wide data inventory to allow more detailed emission studies to be carried out in the context of climate change and other pollution effects.

Crucial to city planning and transport policy today is information about vehicle emissions and, on the global scale, carbon dioxide emissions in particular given their role in anthropogenic global warming. Now, researchers at Boston University have constructed an inventory from the US Federal Highway Administration’s Highway Performance Monitoring System database of roadway traffic. This brings together in DARTE more than three decades of carbon dioxide emissions data from roads across the nation down to a resolution of one kilometre.

Graduate student Conor Gately suggests that early analysis of the DARTE inventory already reveal an ongoing shift in the US towards urban traffic and emissions. "DARTE reveals that urban areas were responsible for 80 percent of the growth in vehicle carbon dioxide emissions since 1980, and for 63 percent of total 2012 vehicle carbon dioxide emissions," he explains. DARTE has also already demonstrated that although planners and researchers often use population density figures to predict local levels of carbon dioxide generation by vehicles, these predictions can vary wildly from reality.

Red flag

Until now, researchers had assumed that there would be a linear relation between population density and driving activity. Ian Sue Wing points out how, "We raise a huge red flag, saying no, that’s not necessarily the way to go. In major urban areas, DARTE can differ from population-based estimates by as much as 500 percent."

Moreover, the received wisdom concerning vehicle emissions is that they should decrease with the implementation of so-called smart growth policies that aimed to promote denser urban residential development. "However," adds Gately, "the most pronounced declines in per capita emissions are only observed in cities that are already very dense such as New York and Boston, while for low- and medium-density cities the effects of densification are much more varied."

These initial comparisons and conclusions reinforce the idea that data is not knowledge and that better information and understanding is critical to improving the perspective planners and policymakers have on traffic pollution in terms of minimize greenhouse gases. Lucy Hutyra adds that, "Although we don't have binding international or national policies yet, over 1000 US cities have made pledges to reduce greenhouse gas emissions. " Unfortunately, large uncertainties in earlier greenhouse gas inventories have made it very difficult for a city to determine if it has actually reduced its emissions, she suggests. "For metropolitan areas that want to address carbon dioxide emissions from their regional economy, knowing where they are is a prerequisite to doing anything about it," Gately adds. "You can’t affect what you can't measure."

Vehicle variables

The DARTE inventory shows just how variable are the emissions trends in different US cities. For instance, when looking at population density it can be seen that this has not changed in a place like Salt Lake City over the time period represented by the data, but the per capita emissions have risen considerably because of significant population growth in the suburbs and residents needing to drive into the city regularly and frequently. By providing a better baseline for such findings, DARTE should help to answer major policy questions in urban development.

There is, of course, disagreement on how vehicle carbon dioxide emissions ought to be reduced for the benefit of us all. Urban planners with costly schemes are effectively in competition with the economists. "Do we tax driving and emissions, and make driving more difficult and more expensive? Or do we change people’s environment, creating inducements or mandates that they will live closer to where they work, walk more, bike more and use more public transit? We don’t know yet which approach will be more effective," explains Wing. "It's also the only sector that is still growing," Gately adds. "We have seen power plant and residential emissions of carbon dioxide decline over the last decade, but transportation is much tougher to de-carbonize."

"We have a few specific next steps in progress," Hutyra told SpectroscopyNOW. "We are currently working with cell phone GPS data to estimate carbon dioxide and criteria air pollutants at high spatial and temporal resolutions, think the city block level with 15 minute resolution.  With this ultra high-resolution data we can assess specific hotspots within cities and policy actions." She adds that, "A couple of initial analyses we are thinking about include exploring how buses frequently stopping on particular roads influence congestion and emissions through induced backups or how changes in the enforcement of double parking laws change congestion. We are also bringing our highly resolved emissions estimates together with new OCO-2 [Orbiting Carbon Observatory] observations of carbon dioxide from space."

Ultimately, the team hopes to improve the quantification of the urban carbon cycle to improve our understanding of greenhouse gas emissions sources and how they are changing within and across cities and over time. "This type of work is central to informing greenhouse gas monitoring, reporting, and verification systems," Hutyra told us.

Related Links

Proc Natl Acad Sci (USA) 2015, online: "Cities, traffic, and CO2 : A multidecadal assessment of trends, drivers, and scaling relationships"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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