Transportation has significant impact on GHG emissions and air quality. Laying out infrastructure and incentives for renewable energy and energy efficiency and transitioning to clean energy can help mitigate GHG emissions.

In 2012, the transportation sector contributed to about 61 percent of total GHG emissions in SMC.[1] Solo driving accounts for most of the GHG emissions by this sector.[2] These high levels of emissions can be attributed to the fact that SMC is located in between two major employment hubs, San Francisco and Santa Clara counties.[3] Idling for more than 10 seconds uses more fuel and produces more emissions that contribute to smog and climate change than stopping and restarting your engine does.[4] That, combined with the lack of affordable housing closer to the workplace, results in an estimated 400,000 workers commuting into, out of, or within SMC. The overall average commute time in SMC has increased from 27.8 minutes in 2015 to 29 minutes in 2016.[5]

Source: On the Map (U.S. Census Bureau, Center for Economic Studies) 

The charts above highlight that more residents commute out rather than work within the county – about 6 out of 10. This number has been steadily increasing since 2002. The graph below highlights that change, showing that whereas nearly 54 percent of residents worked outside the county in 2002, just under 62 percent commuted out of the county in 2017.


Source: On the Map (U.S. Census Bureau, Center for Economic Studies)

In 2019, the American Lung Association’s annual State of the Air report ranked the San Francisco Bay Area among the 10 worst U.S. metropolitan areas for ozone short-term and annual particle pollution. The report gave SMC a D in air quality, which is defined as one week or more of unhealthy air conditions.[6] One reason behind this poor showing is more “super-commuters,” i.e., drivers spending more time on the road to get to and from work.[7] According to Home For All, 83,000 new jobs were created in SMC between 2010 and 2017, but only 7,100 housing units were built.[8] Additionally, many of the jobs created in SMC are not high-paying jobs; half the people working in the county make less than $50,000 a year and cannot afford housing there.[9] In 2016, the annual median home price for single-family homes in SMC was $1.3 million, which increased to $1.58 million in 2018. This is more than 20% increase over a period of two years.[10] The lack of sufficient, affordable housing directly impacts transportation, increasing commute times on a regional level. The State of the Air 2019 report also adds to the evidence that a changing climate is making it harder to protect human health due to worsening ozone and particle pollution. Read the Public Health section of this report to know more about air-quality impacts on health.

Energy use, GHG emissions, and transportation are inextricably linked. San Mateo’s Countywide Transportation Plan 2040 aims to provide cleaner transportation, development of pedestrian and cycling pathways, and more incentives to purchase electric vehicles. The graph below shows transportation emissions in SMC in 2015, and how they are projected to decline by 2040. It is evident that they fall almost one million MTCO2e units below the state’s 2040 goals.

Above Figure: County-wide on-road Transportation GHG emissions and reduction goals.

Source: San Mateo Transportation Programs Climate Impact Report, Nov 2018. Accessed here

Shortage of affordable, interconnected and public transportation and affordable housing near workplaces in SMC impacts low-income people and people of color more than other communities and is a critical indicator of social inequity in response to climate change. To know more about shortage of affordable housing near workplaces and its social impact, read the Housing Council Leadership of SMC’s report. In 2018, SMC voted for a ½% sales tax, Measure W, that will generate $80 million per year in sales tax revenue for the next 30 years to improve public transit, create safer bike and pedestrian routes, reduce traffic, repair roads, and address other urgent community needs[11]. A full 50% of the funds will go to SamTrans, Caltrain, paratransit, and other mobility services to better serve low-income communities and communities of color, youth, seniors, people with disabilities, and transit-dependent populations throughout the county. To read more about this initiative, click here.

Caltrain Electrification is a key component of the CalTrain Modernization Program (CalMod). The current project will electrify the corridor from San Francisco to San Jose and will replace 75% of Caltrain’s diesel service with electric, thereby providing cleaner and greener service to Caltrain users. Phasing of these electric trains are expected to begin in during late 2021.[12]

Public transportation options within the county provide alternative transportation resources, notably to elderly people and those who need more help getting around. The 65+ age group makes  15% of San Mateo County’s population. The proportion of older adults in San Mateo County is projected to rise by 82 percent by the year 2040[13]. The 75+ age group will more than double in that time. A list of public transportation options is available here. March 2019 marked the launch of San Mateo County Mobility Resource Center, an informational program that matches elders with appropriate transportation services. Click here to know more about this initiative.





[3] Transportation. Sustainable San Mateo.




[7] Hagemann, H. (2019), Bay Area Air Quality Takes A Hit In Latest Report,

[8] Source: CA EDD, U.S. Census, American Community Survey. Retrieved from

[9] Moving San Mateo County Forward: Housing and Transit at a Crossroads. Housing Leadership Council. (2018). Retrieved from

[10] San Mateo County Association of Realtors Market Data. Retrieved from





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