Since it involves stop-and-go traffic, city driving was once considered the biggest challenge to maximizing fuel-efficiency in vehicles. That was until modern fuel-efficient technology was developed to minimize the impact stopping and going had on fuel consumption. Breakthroughs in start-stop, hybrid systems, engine design, material sciences, and transmissions have all contributed to more-efficient modern vehicles.
Start-stop works by seamlessly turning your engine off when you come to a stop and, as the name says, starting it again seamlessly when you press the gas pedal to resume driving. The advantage of start-stop is enhanced when combined with hybrid technology. The eAssist motor, and not the gas engine, is moving you from a stop, and fuel consumption is reduced. As you get rolling again, the gas engine can seamlessly take over driving the wheels from the electric motor. And when that engine takes over, it too has been tuned for maximum efficiency.
Modern engines benefit greatly from advancements in direct-injection fuel delivery and variable valve timing (VVT). Direct injection consists of fuel injectors that spray fuel directly into the combustion chambers of the engine. This direct delivery of fuel results in greater efficiency, as the amount of fuel entering the engine is delivered precisely. The amount of fuel and air entering the engine is also done more efficiently thanks to modern VVT — a computer-controlled system that varies the opening and closing of the engine's valves. At certain engine speeds, an engine is more efficient when the valves open at different times. VVT maximizes the efficiency and power of an engine by opening and closing engine valves at the precise time throughout the engine's rev range.
In addition to great advances in electric motor, lithium-ion batteries, and gasoline engine development, material science also plays a key role in modern, fuel-efficient city driving. Advancements in composites and the widespread use of lighter alloys, such as aluminum, means vehicles are light, but also very strong. And since lighter vehicles take less energy to move, fuel mileage improves as well. Transmissions have also been developed to maximize fuel-efficiency in city driving. While driving, you want your transmission in the correct gear for delivering the quickest acceleration but also the best fuel-efficiency. Modern, computer-controlled transmissions precisely choose the best gear for both acceleration and maximum efficiency.
Technology has minimized the impact city driving has had on new vehicles. So much so, that in the city, new cars can often return fuel mileage that was a good number for highway economy in recent times. The 2014 Buick Lacrosse Luxury Sedan returns an EPA-estimated 25 miles per gallon in city driving. You get all the amenities of a modern, luxury sedan with strong fuel mileage, thanks to modern advancements in fuel-efficient technology.