National Geographic : 1981 Feb 28
with a promising future fuel consumption as much as 3 percent. Puncture-prooftires of plastic (12) could save even more andeliminate the cost andweight of a spare tire and wheel. Automatic transmissions in flict a mileage penalty of about 10 percent compared to manual gearboxes. Continuously vari able transmissionspromise even better mileage, as does a stop start engine that shuts down if a car is idling or coasting, cutting gas consumptionby about 15 per cent. A touch on the accelerator restarts the engine. Better lubricants (13) and bearingswill reducefriction,and microprocessors (14) will moni tor systems and command ad justments to keep them at peak efficiency without-even despite - a ctions by the driver. As the price of petroleum for gasoline and diesel engines con verges with that of alternate en ergy sources, new power systems should become widely available, probably beginningwith battery powered electric motors (15). Their advantages:quietness, low pollution, and simplicity. Their disadvantages:limited range be tween recharges (which are also limited), weight, and bulk. New battery systems now under test ing and development should give better performance. Efficiency may also be increased by using flywheels (16) to equalize power demands on batteries during ac celerationand hill climbing. Electric motors may be paired with smallcombustion engines in hybrid systems (17)-electric powerfor low speeds, combustion for highway cruising. Power systems that run on compressed gases such as pro pane, methane, or hydrogen are more problematicalfor the per sonal car. Range is limited, dis tribution systems are not in place, and each station pump could cost $30,000. It remains moot whether so-calledsynthetic fuels (pages 74-94) could best be used directly in engines or to gen erate electricity. Other combustion engines such as the gas turbine or exter nal combustion may become op tions in the 1990s. Proper maintenance of roads can improve mileage 5 percent. And since combustion engines operate best at about 40 mph, traffic ideally should be speeded up in cities and slowed down in the country-theformer difficult though possible, the latter un popularand impractical.