A word of caution about the Model S, Tesla Motors' new electric sedan: The S stays smooth and silent, even when it's flying down the highway. Absent gears, engine noise or any vibration that doesn't originate with a pothole, it's absurdly easy for Model S drivers to shred speed limits without the slightest clue. Depending on the range of the battery pack and other options, Model S prices range all the way from $57,400 to $105,400 before state and federal incentives. The Model S functions much like a typical, automatic transmission sedan. But it's not quite the same. Put the car in drive and take your foot off the brake pedal, for example, and the S doesn't go anywhere. It just sits there until you touch the accelerator. Push the accelerator, and the car responds instantly. There's no sense of an engine laboring to pick up speed. Like other electric vehicles, the Model S uses regenerative braking. The brakes capture some of the moving car's kinetic energy, convert it to electricity and use it to recharge the battery while you drive. It's one of the ways a Model S with the most expensive battery pack option can drive more than 300 miles without plugging in. With the Model S, the regenerative braking starts the moment you ease off the accelerator pedal. The drop in speed is so pronounced that the car's brake lights will go on, even before you touch the brake pedal itself. It feels almost like having two separate braking systems working at the same time.