Topic:
GASOLINE; ENVIRONMENTAL PROTECTION (GENERAL); EMISSION CONTROLS; ENVIRONMENTAL POLICY; MOTOR VEHICLES;
Location:
MOTOR VEHICLES - EMISSION CONTROL SYSTEMS;

OLR Research Report


July 8, 2004

 

2004-R-0523

EFFECT OF REPLACING CONVENTIONAL VEHICLES WITH HYBRID VEHICLES

 

By: Paul Frisman, Associate Analyst

You asked what the impact would be on (1) emissions and (2) gasoline consumption if hybrid vehicles replaced conventionally-powered vehicles in Connecticut.

SUMMARY

We rely on two reports prepared for the Electric Power Research Institute (EPRI) in 2001 and 2002. The reports found that hybrid compact cars could reduce smog-forming gases by 10% over their conventional counterparts, and hybrid midsize cars, midsize sport utility vehicles (SUVs) and full-size SUVs could reduce those gases by 15%, 19% and 21% more than their conventional counterparts, respectively. Smog-forming gases include (1) nitrogen oxides (NOx), and (2) hydrocarbons (HC) and other volatile organic compounds (VOCs).

The Department of Environmental Protection (DEP) estimates that passenger cars in the state emit approximately 45.5 tons of VOCs and about 43 tons of NOx daily. DEP estimates that SUVs, vans and light-duty trucks emit 39.5 tons per day of VOCs and 51 tons daily of NOx.

Hybrid passenger cars would reduce the amount of smog-forming gases they generate by between 10% and 15%, depending on the proportion of compact cars. Therefore we would estimate that hybrid passenger cars would reduce VOC emissions by 4.5 tons to 6.8 tons per day, and reduce NOx emissions by 4.3 tons to 6.5 tons a day. Total smog-forming emissions from hybrid passenger cars would therefore be reduced between 8.8 and 13.3 tons daily.

The estimates for SUVs, vans and light duty trucks are somewhat less reliable, because EPRI did not evaluate pickup trucks or vans. Assuming reductions similar to the 19%-21% range of SUVs, however, we would estimate that hybrid SUVs, light-duty trucks and vans would reduce VOC emissions by between 7.5 and 8.3 tons a day, and NOx emissions by between 9.7 and 10.7 tons a day. Total smog-forming emissions from hybrid SUVs, light trucks and vans would therefore be reduced between 17.2 and 19 tons daily.

Total daily HC/VOC reductions for hybrid passenger cars, SUVs, light duty trucks and vans would therefore range from 12 to 15.1 tons daily; total NOx reductions would range between 14 and 17.2 tons daily; and total smog-forming gas reduction would range from 26 to 32.3 tons daily of the total 180 tons a day generated by these vehicles.

We should note these estimates do not consider such variables as the type of hybrid vehicle, driving patterns, the types and age of the passenger fleet, or the pollutants emitted by heavy-duty trucks. We also assume we are instantaneously replacing the existing motor vehicle fleet with hybrid vehicles. In reality, however, it takes about 10 years for 80% of a motor vehicle fleet to turn over. Also, any significant difference in emissions from conventional and hybrid vehicles would presumably diminish significantly beginning in the 2008 model year, when hybrid and conventional vehicles sold in Connecticut, including SUVs and light trucks, must comply with the same emission standards.

The EPRI studies also found that hybrid compact cars would consume 21% less gasoline than their conventional counterparts, and that midsize cars, midsize SUVs and full-size SUVs would use 25% less, 31% less, and 32% less gasoline, respectively, than their conventional counterparts. Reduction in emissions of carbon dioxide (CO2), which is thought to contribute to global warming, would be comparable to the decrease in gasoline consumption.

Presumably, hybrid vehicles' more fuel-efficient engines would also reduce carbon monoxide and particulate matter (soot) emissions. However, we were unable to locate data on hybrid vehicles' particulate emissions.

SMOG-FORMING POLLUTANTS

Ground-level ozone, sometime called smog, is formed when NOx, HC, and other volatile organic compounds react on hot sunny days. These precursor elements are present in many common pollutants including tailpipe emissions, smokestacks, paints and solvents. Ground-level ozone is a significant health risk. It irritates the respiratory tract and interferes with normal lung functions, causing breathing difficulties, aggravation of heart and lung disease and asthma, coughing, eye irritation, sore throat, and headache.

The U.S. Environmental Protection Agency (EPA) has found Connecticut in nonattainment with its 8-hour ozone standard, which means the state must take steps to reduce ozone levels. EPA plans to designate nonattainment areas for fine particulate matter (particles 2.5 microns in diameter or smaller) by the end of the year.

HYBRID VEHICLES

Hybrid electric vehicles (HEVs) use two or more sources of power. Most commonly, hybrids use electricity from batteries and mechanical power from small, gasoline-fueled internal combustion engines. Conventional vehicles use only internal combustion engines. Using both electricity and smaller engines allows HEVs to make more efficient use of gasoline.

There are different types of HEVs. In some (“series” design), the engine never directly powers the car. Instead, it drives a generator, which can either charge the batteries or power an electric motor that drives the wheels. In others (“parallel” design), either the engine or the generator/motor can supply power to the wheels, depending on the type of driving. The Toyota Prius, one of the world's first mass-produced HEVs, combines series and parallel technologies. In a third kind (“split” design), the engine drives one axle and the electric motor the other.

The EPRI studies considered only parallel hybrid configurations, and did not compare conventional vehicles to commercially available HEVs, such as the Prius. They instead compared them to hybrid vehicle designs based on four conventional vehicle “platforms” – a Saturn (compact car), Chevrolet Lumina (midsize car), Ford Explorer (mid-size SUV) and Chevrolet Suburban (full-size SUV).

EPRI STUDIES

This report is based on “Comparing the Benefits and Impacts of Hybrid Electric Vehicle Options for Compact Sedan and Sport Utility Vehicles” (EPRI Technical Report 1006892). We link to the full report here. A similar EPRI report on mid-size hybrid vehicles, “Comparing the Benefits and Impacts of Hybrid Electric Vehicle Options,” (EPRI Technical Report 1000349) is linked here. EPRI was founded in 1973 as a nonprofit research consortium for the electric utility industry.

The studies concluded, among other things, that gasoline-fueled hybrid electric vehicles could be designed to be comparable to and operate like currently available conventional vehicles, and that they would offer improved efficiency, reduced emissions and reduced petroleum dependency. They assumed commercial availability of vehicles in 2010, incorporating technology reasonably likely to be available by then.

It examined hybrids without electric range capability (comparable to the Prius, Honda Insight and Honda Civic Hybrid). It also examined “plug-in” hybrids with all-electric range capability of up to 60 miles. Since, as the report notes, no major carmaker was planning to develop and introduce plug-in hybrids, this report does not discuss them.

EMISSIONS

The EPRI studies determined environmental impacts of both HEVs and conventional vehicles over the “wells-to-wheels” fuel cycle – that is, it took into account all emissions associated with the extraction, processing, distribution and final use of the energy used by the vehicles as well as the emissions from the vehicle itself. This includes emissions from extracting and processing of crude oil and distributing the fuel.

The studies found that compact hybrids could reduce smog forming gases by 10% over their conventional counterparts, and that midsize cars, midsize SUVs and full-size SUVs could reduce those gases by 15%, 19% and 21%, respectively.

They found that compact hybrids could reduce CO2 emissions by 21% over their conventional counterparts, and that midsize cars, midsize SUVs and full-size SUVs could reduce CO2 emissions by 28%, 31% and 32%, respectively.

The following tables indicate the annual total emissions of NOx, hydrocarbons (HC) and CO2 of the four types of conventional vehicles and their hybrid counterparts.

Table I: Compact Cars

 

Conventional Compact

Hybrid Compact

Percentage Difference

HC (grams)

799

692

-13.4%

NOx (grams)

393

381

-0.3%

Total Smog Precursors (grams)

1,192

1,073

-10%

CO2 (kg)

4,286

3,398

-21%

Table II: Midsize Cars

 

Conventional Midsize

Hybrid Midsize

Percentage Difference

HC (grams)

947

763

-19.4%

NOx (grams)

411

389

-5.4%

Total Smog Precursors (grams)

1,358

1,152

-15%

CO2 (kg)

5,518

3,988

-28%

Table III: Midsize SUVs

 

Conventional SUV

Hybrid SUV

Percentage Difference

HC (grams)

1,155

887

-23%

NOx (grams)

435

404

-7%

Total Smog Precursors (grams)

1,590

1,290

-19%

CO2 (kg)

7,253

5,018

-31%

Table IV: Full size SUVs

 

Conventional SUV

Hybrid SUV

Percentage Difference

HC (grams)

1,346

1,005

-25%

NOx (grams)

458

418

-8.7%

Total Smog Precursors (grams)

1,804

1,422

-21%

CO2 (kg)

8,841

6,002

-32%

FUEL EFFICIENCY

The studies found that hybrid compact cars consumed 21% less gasoline than their conventional counterparts, that midsize cars, and that midsize SUVs and full-size SUVs 25% less, 31% less, and 32% less, respectively, than their counterparts.

The following tables indicate the estimated city and highway gas mileage of the four conventional vehicles and their hybrid equivalents.

Table I: Compact Cars

Conventional Compact

Hybrid Compact

Percentage Difference

City Mileage

28.44 mpg

43.66 mpg

+53.5%

Highway Mileage

38.45 mpg

39.38 mpg

+2.4%

Table II: Midsize Cars

Conventional Midsize

Hybrid Midsize

Percentage Difference

City Mileage

20.88 mpg

36.54 mpg

+75%

Highway Mileage

32.29 mpg

34.09 mpg

+5.6%

Table III: Midsize SUVs

 

Conventional SUV

Hybrid SUV

Percentage Difference

City Mileage

16.56 mpg

27.54 mpg

+66%

Highway Mileage

23.17 mpg

28.47 mpg

+23%

Table IV: Full-size SUVs

 

Conventional SUV

Hybrid SUV

Percentage Difference

City Mileage

13.41 mpg

23.04 mpg

+72%

Highway Mileage

19.34 mpg

23.79 mpg

+23%

FURTHER INFORMATION

The Union of Concerned Scientists, in a January 2003 report entitled “A New Road: The Technology and Potential of Hybrid Vehicles” also found improvements in fuel efficiency and reductions in smog-forming emissions. We link to that report here.

PF:ts