Better Designed Roadways Will Reduce Greenhouse Gas Emissions from Vehicles.

As discussed in [addressee and further motivation for document is omitted], transportation and vehicles account for roughly one-third of greenhouse gas emissions.[1]  The premise of this writing is to put forth the argument that better infrastructure - including more adequately designed and modern roadways to reduce vehicular traffic congestion - would help to decrease carbon emissions and pollutants from transportation sources and thereby reduce carbon footprints and any subsequent accumulation of Green House Gases (GHGs) in the atmosphere as a result. 

Most of the nation’s interstates and highways were designed in excess of five decades ago when the population of most urban areas was merely a fraction of what the respective populations are today – increased population which is exacerbated by the number of cars on the roads to service the larger populace.[2]  Such a proposed paradigm of better designed roadways also creates further positive externalities including less pollution as well as more jobs to build and maintain roadways – though there is some debate as to which transportation projects build more jobs, i.e.: public transportation v. public roadways and jobs creation.[3] 

While this sensitive subject and corresponding argument is vastly more entailed than can be completely addressed by this short writing, this note is to nevertheless address the framework for such an argument.  Regardless, any Climate Action Plan (“CAP”) that does not allow for the increased capacity of roadways to handle the ever-increasing in-flow of residents who will likely own cars seems off-base and lacking in foresight.  Lack of how to properly mitigate any greenhouse gas difficulties that the region currently and continues to face into the future seems unrealistic without significantly reducing traffic congestion – especially concerning freeway congestion.[4]

The amount of pollution created by an internal combustion engine vehicle correlates to the amount of fuel a vehicle’s engine burns.[5]  Driving less therefore would decrease pollution from vehicular sources by running the vehicle’s engine less.[6]  Of course, driving less would seem to correspond to spending less time while driving in one’s vehicle as well.

As a common sense example of unnecessary pollution from vehicles, automobiles tend to burn much more fuel when traversing any given 30 miles in the timespan of an hour and a half (i.e.: at 10 miles per hour, “mph”) due to traffic congestion on the scale of “city traffic” (e.g..: repeatedly stopping and starting) as opposed the amount of fuel burned when traveling the same 30 miles on the freeway at normal uncongested freeway speeds which would take approximately 30 minutes (say, at 60 mph).[7]  In other words, the matter seems one of common sense that better fuel efficiency ultimately pollutes less and better fuel economy is generally not available to the fuel-burning engines of vehicles that are sitting idle in traffic and therefore going no miles for the gallons of gas the vehicle burns while sitting in the traffic congestion – as often seems typical for much of the nation’s highways during rush-hours. 

The lesser fuel economies/efficiencies from vehicular sources include vehicles inching-along in bumper-to-bumper traffic as opposed to a vehicle that is getting more miles per gallon by moving at unfettered freeway speeds.[8]  From a numbers point of view and considering all external factors to otherwise be equal, while a vehicle could burn twice the amount of fuel for a given timespan at 70 mph as opposed to idling in bumper-to-bumper traffic for the same time period, if traveling at 70 mph takes one third the amount of time compared to traveling in bumper-to-bumper traffic, ultimately the freeway travel speed will consume less fuel and therefore likely pollute less because the vehicle spends significantly less time on the roadway and also maintains significantly increased fuel efficiencies as well.[9]  The realities of less pollutants from vehicles traveling at freeway speeds are further illuminated when viewed in light of the realities of modern vehicle emission controls systems[10] and the torturous time-consuming crawl of most highway traffic congestion situations.[11]

For instance, while a car arguably may release more GHGs when it is motoring at 70 miles/hour (level-ground cruising at 70 “mph,” typically at 2000 rpm) as opposed to when it is idling and sitting still (0 mph, yet 1000 rpm), when a vehicle is idling or sitting motionless in one place then the amount of GHGs emitted are concentrated or more dense per area polluted than compared to the vehicle that is motoring by at a speed of 70 mph.[12]  However, even such an assumption/comparison is unlikely to be valid given modern emissions controls as some internal combustion engine by-products/pollutants decrease at higher speeds.[13]  Furthermore, those GHGs that are released during a non-moving idling period are emissions/pollutants that essentially resulted in no productive work either (as work is physically defined as a force moving/working over a distance).[14]  And again, Barth et.al. displayed that cruising at constant normal travel speeds tends to burn less fuel and pollutes less – with freeway congestion being the most inefficient fuel consumption and the larger comparative source of pollutants, especially in light of the stop and start driving realities of traffic congestion.[15] 

As this writing has attempted to display, traffic congestion is likely a major contributing factor to vehicle emissions and pollutants.  And as anyone who has ever undergone the misery of having to travel 30 miles or more in bumper-to-bumper freeway/highway traffic can attest, the roadways of our nation are seriously under-designed and outdated for the volume of traffic to which the roads support in most of the nation’s urban regions.  The literature seems to extend ad nauseam concerning the increased volume and density of pollutants from vehicles in traffic congestion – as discussed herein and above.  For any government entity to currently gamble on the adequacy of future plans to reduce vehicular traffic and to concurrently ignore the inadequacy of nation’s highways and roadways, that government entity seems more than short-sighted. This writer believes that our nation would be well-served to start building modern and adequate roadways to support the level of traffic to which those roads are modernly subjected (and allow room for continued expansion as well).  To rely on the outdated designs and traffic estimates of 1960 – which is when most of the nation’s interstates and highways were designed and built, seems misguided.

Adam Trotter P.E.
May 2017.

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[1] How Does the Release of Car Exhaust Fumes Cause Global Warming?; by J.T. Barett, SEATTLE PI, located at: http://education.seattlepi.com/release-car-exhaust-fumes-cause-global-warming-3682.html.  Also see:  Road Transportation Emerges as Key Driver of Warming, Feb. 18, 2010, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION, Goddard Institute for Space Studies, located at: https://www.giss.nasa.gov/research/news/20100218a/.

[2] For example, San Diego County’s population has tripled from 1,000,000 to over 3,000,000 since 1960. From: Population.us, located at: http://population.us/county/ca/san-diego-county/#2.  For sake of illumination, the Greater Los Angeles population is currently approaching 19,000,000, also three times the population in 1960, from: Population Growth in California, located at: http://cgge.aag.org/PopulationandNaturalResources1e/CS_US_July09/CS_US_July094.html.  See also:

Density, Car Ownership, and What It Means for the Future of Los Angeles, By Damien Newton,  Dec 13, 2010, STREETSBLOGLA.ORG, located at: http://la.streetsblog.org/2010/12/13/density-car-ownership-and-what-it-means-for-the-future-of-los-angeles/.

[3] For example:  “According to data sent by the states to Congress, the states that created the most jobs were the ones that invested in public transportation projects and projects that maintained and repaired existing roads and bridges.”, New report reveals smart transportation spending creates jobs, grows the economy, SMART GROWTH AMERICA, February 4, 2011, located at: https://smartgrowthamerica.org/new-report-reveals-smart-transportation-spending-creates-jobs-grows-the-economy/.

[4] For instance, see:  San Diego Climate Action Plan (CAP), which only superficially, at best, addresses vehicular freeway congestion.  Located at: https://www.sandiego.gov/sites/default/files/final_july_2016_cap.pdf

[5]  “Fuel Economy And Air Pollution.  The amount of co2 emitted by a vehicle is essentially proportional to the amount of fuel burned.”, Global Warming.  GREENCARS.ORG, located at: http://www.greenercars.org/automobiles-environment/global-warming.  

[6] How much air pollution comes from cars?, by Linda C. Brinson, HOW STUFF WORKS,COM, located at: http://auto.howstuffworks.com/air-pollution-from-cars.htm.

[7]“A key element in assessing the EPA rating for a vehicle's average fuel economy (EPA combined) is the split between highway and city driving. Almost all cars and trucks deliver better fuel economy while cruising at 55 mph on the open highway than they do while stopping and starting at low speed on city streets.”; Here's Why Real-World MPG Doesn't Match EPA Ratings.  Why Your Car Could Have an MPG Gap, by John O'Dell, EDMUNDS .COM, Sept. 2012,  located at: https://www.edmunds.com/fuel-economy/heres-why-real-world-mpg-doesnt-match-epa-ratings.html.

[8] “This is because carbon dioxide emissions are directly related to the amount of fuel consumed.”, Gasoline Vehicles.  Learn More About the New Label. U.S. DEPT.OF ENERGY, located at:  https://www.fueleconomy.gov/feg/label/learn-more-gasoline-label.shtml.

[9] See: “Car makers can meet these targets through improved fuel efficiency and an alteration to their mix of models using only current technology.”  Green Peace Worldwide, located at: http://www.greenpeace.org/international/en/campaigns/climate-change/cars/questions-answers/. Also see, for instance, Footnote 7, supra.

[10] See:  Emission Control Devices, located at: http://www.mopar.ca/en/partsandaccessories/emission-control-devices.html.  Also see, Footnotes 7 and 8, supra.

[11] “As mean speed increases, the travel time on a link decreases even though the emission rate tends to increase.  The resulting estimates of total emissions for the example case study are shown in Figure 5.  These results indicate that the total emissions tend to decrease as mean speed increases.  Of course, an increase in mean speed is associated with a decrease in travel time.  The speed profiles for higher average link speeds typically have more constant cruising speed, whereas the speed profiles for lower average link speeds may have more deceleration and acceleration events.  The latter, in particular, can lead to higher total emissions.  The total emissions on one trip depend on both on the travel time and the average emission rates, but are influenced by micro-scale events.  For example, driving situations, whether caused by driver behavior or traffic flow problems, that lead to increased frequency of acceleration events can lead to higher average emission rates.”, Speed and Facility-Specific Emission Estimates for On-Road Light-Duty Vehicles based on Real-World Speed Profiles. By H.Christopher Frey PhD., et.al. North Carolina State Univ., 2006. 

[12] Driving for Fuel Economy, by Larry Webster  CAR and DRIVER Magazine; August 2006, located at: http://www.caranddriver.com/columns/driving-for-fuel-economy.  See also: Vehicle Emissions in Congestion: Comparison of Work Zone, Rush Hour And Free-Flow Conditions, by Kai Zhang, et.al., ATMOSPHERIC ENVIRONMENT 45 (2011) 1929 – 1939, located at: https://sph.uth.edu/kaizhang/files/2014/02/Zhang-2011-AE.pdf.  See also:  No idle matter, TRAFFICTECHNOLOGYTODAY.COM, located at: http://www.traffictechnologytoday.com/features.php?BlogID=718.

[13] “Policy makers have placed less attention on reducing CO2 emissions by reducing traffic congestion. As traffic congestion increases, so too do fuel consumption and CO2 emissions. … If congestion reduces the average vehicle speed below 45 mph (for a freeway scenario), CO2 emissions increase. Vehicles spend more time on the road, which results in higher CO2 emissions. Therefore, in this scenario, congestion mitigation programs will directly reduce CO2 emissions.”; Estimating Emissions and Fuel Consumption for Different Levels of Freeway Congestion, M.Barth, et.al., TRANSPORTATION RESEARCH RECORD 1664, Paper No. 99-1339; located at:  http://cmscert.engr.ucr.edu/cmem/docs/TRR1999-Different-Congestion.pdf.  See also: Traffic Congestion and Greenhouse Gases, by M. Barth, et.al., ACCESS, 

[14] “Work is done when a force that is applied to an object moves that object. The work is calculated by multiplying the force by the amount of movement of an object (W = F * d). A force of 10 newtons, that moves an object 3 meters, does 30 n-m of work.”, PHYSICS4KIDS.COM, located at: http://www.physics4kids.com/files/motion_work.html.

[15] Estimating Emissions and Fuel Consumption for Different Levels of Freeway Congestion, M.Barth, et.al., TRANSPORTATION RESEARCH RECORD 1664, Paper No. 99-1339; located at:  http://cmscert.engr.ucr.edu/cmem/docs/TRR1999-Different-Congestion.pdf.