By accelerating hard, you're burning a lot more gasoline than you would when you gain speed smoothly. And it will waste even more while idling at the next traffic light until the driver who accelerates slowly arrives. Conventional wisdom says that the hare starts to consume more fuel. But it turns out that increasing speed to the limit too slowly also reduces miles per gallon.
How can that be? Cars get lower fuel economy in lower gears and accelerating too slowly prevents upshifting at an efficient pace. The best acceleration speed varies depending on the vehicle, gear ratios, and weight. But in our tests, we found that taking 15 seconds to accelerate to 50 mph consumed less fuel than taking 30 seconds to reach the same speed, because the car entered its highest gear and saved fuel sooner. Both options have their strengths and weaknesses, but in general, it's best to accelerate slowly.
From a fuel efficiency standpoint, accelerating too fast is costly. In addition, rapid acceleration, along with sudden braking, could cause wear and tear on your vehicle. On the other hand, accelerating too slow can also damage your car. My dodge neon (automatic), driving conservatively with slow acceleration, gave an estimate of 26 mpg, driving like an imbecile gave an estimate of 29 mpg.
Combining trips can save you time and money by avoiding unnecessary stops and starts of your vehicle, which can be a problem in colder climates, where the engine takes longer to reach its most fuel-efficient temperature. Now, obviously, when you accelerate harder, more fuel is pumped into your engine, but the sooner you'll get to that cruising sweet spot where fuel consumption is much lower. Maintain cornering speed so you don't have to accelerate as much at the start, wasting fuel. However, that's really the case if you drive your car with the accelerator open everywhere you go or step on the accelerator at every green light.
With a manual transmission, what you would do with the curve in the previous example would be to have the throttle with the throttle open from 1500 to 2500 rpm and change to 2500 rpm for each gear. According to NRCAN, the best way to accelerate your car smoothly is to take 5 seconds to accelerate it to 12.5 mph (or 20 kilometers per hour) from a stop. According to a Toyota blog post, one of the best ways to accelerate your vehicle is to gently press the accelerator pedal. In neutral, it has no way of accelerating to avoid danger, and if the engine stalls, it has no power steering or vacuum impulse for the brakes.
There are those who refuse to be shaken by the practice of going downhill into a standstill to save gas. Most cars have an ideal range in which raising the accelerator reduces acceleration a lot and lowering it further doesn't increase it much; that's the magic point where I tend to stay. You should try to accelerate only when you leave your starting point and brake only when you reach your destination. My wife drives it like a granny: nice slow acceleration, anticipation to brake, gets around 12-14 mpg average.
My recipe for overall good fuel economy is smooth acceleration, but not super slow, and then putting the car into the highest gear your car can comfortably be in.