Senators Wiener and Ashby Introduce Legislation To Cut Climate & Air Pollution From Transportation Infrastructure

February 7, 2023



February 7th, 2023


Senators Wiener and Ashby Introduce Legislation To Cut Climate & Air Pollution From Transportation Infrastructure


SACRAMENTO – Senators Scott Wiener (D-San Francisco) and Angelique Ashby (D-Sacramento) introduced Senate Bill 312, which will reduce the climate and health impacts of California’s roads and other transportation infrastructure by lowering the carbon and pollution emitted by asphalt. SB 312 creates a pilot program and authorizes payments to Caltrans contractors that use the lower carbon forms of asphalt known as warm mix asphalt (WMA).

“We have a proven technology that will reduce a significant source of emissions for a relatively low cost,” said Senator Wiener. “We should be using low carbon asphalt across the state. SB 312 incentivizes state contractors to make the switch, resulting in lower greenhouse gas emissions and cleaner air that will benefit our public health, particularly in the communities of color where that are disproportionately impacted by this industry.”

Asphalt is a major source of emissions, both during the mixing process and while it is being laid. It is used to surface 94% of roads in the U.S., and in the traditional process, asphalt is mixed between 300 and 350 degrees Fahrenheit, requiring massive amounts of fuel. This process also releases PM, SO2, CO, and NOX, harmful pollutants that contribute to a variety of respiratory and other health conditions.

As the transportation agency for the world’s fifth largest economy, Caltrans is a significant consumer of asphalt. In 2020 alone, Caltrans utilized 3,405,088 metric tons of asphalt across 443 construction paving projects. With an average carbon intensity of 50.2 to 52.1 kg CO2e/ton of mix produced, Caltrans’s use of asphalt emitted roughly 174 million tons of greenhouse gas (CO2 equivalent) in 2020 alone.

The impacts of the state’s asphalt production and use fall disproportionately on industry workers and communities of color, where asphalt mixing plants are typically located. Asphalt produces billowing clouds of odor and pollutants that flows into the surrounding community, and the workers must contend with extremely high temperatures as well.

To meet California’s climate goals and protect public health, this source of pollution must be eliminated. Industry players are working to develop zero-carbon alternatives to traditional asphalt, but several mature lower-carbon alternatives already exist.

Warm mix asphalt (WMA) is a category of asphalt produced at a lower temperature, generally between 30 to 70 degrees Fahrenheit below that of its hot mix counterpart. These lower temperatures remain throughout the production, transportation, and paving processes.

Because of this reduced need for high temperatures, warm mix asphalt requires 20-35 percent less fuel consumption, with some estimates as high as 50 percent. These reductions place a sizable dent in the climate impact of asphalt use. The reduced temperatures also reduce levels of the other associated air pollutants - depending on the type of warm mix asphalt, reductions can be over 50% of SO2, NOX and CO. These changes improve working conditions for workers and air quality and public health for surrounding communities.

WMA also offers engineering and cost benefits for road pavement. In a 2021 report from Caltrans, the agency noted that warm mix asphalt results in better compaction on the road. This type of compaction can result in easier pavement processes, shortening the time and lowering the cost of labor required by traditional asphalt. This better compaction can also result in longer road life cycles, meaning re-pavement is not required as often. 

WMA also extends the time that paving can be conducted, because it is less sensitive to variations in moisture and temperature than hot mix asphalt. By enabling contractors to pave later into the winter and at night, WMA reduces project costs and disruption on surrounding neighborhoods.

Warm mix asphalt is already widely recognized, and has been used in nearly every state. The National Asphalt Pavement Association estimates that over 40% of the current asphalt market in the United States is served by WMA.

SB 312 will speed California’s adoption of warm mix asphalt by authorizing a payment of $3 per ton of asphalt mixed between 251 and 275 degrees Fahrenheit and $5 per ton of asphalt mixed at or below 250 degrees Fahrenheit. 

SB 312 is co-authored by Sen. Angelique Ashby (D-Sacramento).

“It’s an honor to stand with my colleague Senator Scott Wiener to meaningfully address carbon emissions,” said Senator Angelique V. Ashby (D-Sacramento.) “SB 312 works diligently and intentionally towards achieving California’s ambitious climate goals.”