Transportation Energy Efficiency

Fuel economy and efficiency are concerns for all of us who drive. There are practices that help in maximizing fuel use which every driver should know.

Speed

According to the U.S. Environmental Protection Agency and the Oak Ridge National Laboratory, a vehicle loses about one percent in fuel economy for each one mile per hour driven above 55 m.p.h. Although this formula should be adjusted for different car models and ages, we could say, for example, that a passenger car which averages 30 miles per gallon at 55 m.p.h. could get 28.5 m.p.g. at 60 m.p.h., 27 m.p.g. at 65 m.p.h., and 25.5 m.p.g. at 70 m.p.h.

Air Conditioners

One of the major factors affecting auto fuel efficiency is the use of an air-conditioner. Its use during a hot summer day can actually decrease mileage by 21 percent. If the temperature is not too hot, it would be economical to use the flow-through air vent instead. Be aware that having open windows while driving on an expressway can create a wind drag that will lower mileage.

Idling

According to the U.S. Department of Energy, if 145 million passenger vehicles idle for five minutes a day, approximately four million gallons of gasoline are consumed--wasted in staying stationary! Idling is sometimes necessary in traffic jams, but while waiting at drive-in windows, it is more economical to cut the engine if the wait is longer than 30 seconds. Starting up your car again actually uses less gasoline.

In colder climates it is not necessary to warm-up a vehicle for more than one minute. It is more energy efficient to start the engine, take time to attend to driving preparations such as seat belts, side view and rear view mirrors, and traffic before beginning to drive. Your car will have reached optimum performance temperatures with a few miles of even and slow driving, without wasting gas through excessive idling.

Gasoline and Oil

A fuel's octane is the measure of its anti-knock quality only and is not an indicator of its power. Most vehicles (about 80%) are engineered to use regular unleaded gasoline, but many people believe using a premium grade will improve their vehicle's performance. The Owner Manual for your vehicle states the correct grade of gasoline to use for optimum performance. Use it to save money. It also takes more crude oil to refine a gallon of premium gasoline than to refine regular gasoline. According to the U.S. Department of Energy, if all U.S. drivers bought the correct fuel octane, more than one billion gallons of gasoline could be saved each year.

Your choice of engine oil also affects fuel economy and the best type will be recommended in your Owner's Manual. The correct oil will be based on the lowest temperatures expected for the period the oil is in the engine. If you change your vehicle's oil yourself, be sure to dispose of the used oil in the appropriate manner and place. The Maryland Environmental Service can give you the closest recycling site. Their telephone number is: 1-800-I-RECYCLE.

General Driving Tips

There are good driving practices that make a significant difference in fuel efficiency:

  • Gentle and steady acceleration can decrease mileage up to 12 percent.
  • Steady travel speed saves fuel. If you have a cruise control, use it.
  • A tuned engine is important for proper function of spark plugs, fuel system and emission control. An un-tuned engine can cause wasted fuel costs of 15% or more.
  • Under inflated tires of approximately 8 pounds (quite common) increases rolling resistance of the tires by 5%. This can cost about $2.30 a month in wasted gas.
  • Unbalanced wheels which are only 1/4" out of alignment cause rolling resistance of another 2% wasted fuel and increases tire wear.
  • Awareness of traffic tie-ups and accidents allows you to take alternate routes. Listen to the radio stations that carry these frequent road condition reports.
  • Cooling system thermostats can be stuck in the open position. This causes an engine to run too cool and will reduce engine efficiency by about 7% or $3.20 per month.

All of these factors may add up to monthly costs of almost $12. The costs are significant on a yearly basis, but also influence safety and exhaust emissions--two factors which can have enormous price tags for everyone.

Buying a New Car

You may be interested in perusing the U.S. Department of Energy's Fuel Economy web site which gives a fuel economy comparison of all car models available in the United States. It also provides links to local gas price information, emission test results, and crash test results giving helpful information for choosing the right automobile.

Alternative Fuel Price Report

Prices of U.S. alternative fuels and their relation to gasoline and diesel prices are published quarterly in the Clean Cities Alternative Fuel Price Report. You can read the latest report dated July 3, 2001 here.