How Green is Your Car? 
February 2009 | by George Webb, 10th Street

The Del Mar City Council created the Energy Issues Advisory Committee to advise it on energy issues such as renewable energy for municipal, residential and business buildings, energy efficiency and renewable energy sources, and to promote clean and reliable energy savings options in Del Mar. As part of that general effort, and to place our energy use in context, the committee reviewed daily fuel consumption of traffic in Del Mar and its role in greenhouse gas emissions. The results are interesting.

SANDAG (San Diego Association of Governments) compiles average daily volumes of vehicle traffic from data collected by local jurisdictions and Caltrans. Vehicles are defined as motor-driven cars, trucks, buses, vans and motorcycles. SANDAG finds that each weekday 25,000 vehicles pass through downtown Del Mar on Camino Del Mar between 15th and Del Mar Heights Road (average 1999-2003). Importantly SANDAG also finds that a total of 109,000 vehicle miles are driven each weekday within Del Mar city limits (average 1999-2003). The majority of the 109,000 vehicle miles, 97,000 miles (89%) are on Del Mar arterial or collector streets and the balance of 12,000 miles (11%) on local streets.

Who is driving these vehicle miles? Del Mar has about 4500 residents. If, for example, half of them are driving on a given day then a traffic volume of 109,000 vehicle miles would imply that an average Del Mar resident-driver travels 48 miles per weekday within the city. Since Del Mar has only 23 miles of arterial and local streets combined, this travel distance appears to be several times too large to be just Del Mar resident-drivers. It must be due predominately to non-resident drivers commuting through town or visiting the beach and local merchants.

What are some consequences of Del Mar traffic? Since weekend traffic is expected to be somewhat lower than weekday due to the drop off of commuters through town, we estimate that the daily Del Mar traffic volume averaged through the week is about 100,000 vehicle miles per day. How much gasoline is consumed per day? The EPA reports US average auto fuel economy (2008) in the range 15 to 21 mpg depending on driving habits, etc. If, for simplicity, we assume an average fuel economy of 20 mpg per vehicle, then the total daily vehicle fuel consumption in Del Mar is 5,000 gallons per day. Since each gallon of gasoline consumed produces 20 lbs of carbon dioxide, traffic releases 100,000 lbs of carbon dioxide in Del Mar on an average day. For the year, motorists in Del Mar consume 1.8 million gallons of gasoline and release 36 million lbs of carbon dioxide into the atmosphere.

More difficult to estimate, but also a concern, are the levels of trace gases which accompany the daily 100,000 lbs of carbon dioxide tailpipe emissions. These include oxides of nitrogen and sulfur, carbon monoxide, and unburned hydrocarbons all of which are known to negatively affect health.

In the interest of community health and the environment it seems clear that we should encourage more-efficient less-polluting cars in town, promote the use of public transportation, and try to influence driving patterns to minimize emissions. It would be good for us and good for the planet.