You can set Redline to use a manual transmission to shift up (default key - a) and down (default key - z) through the gears.
You can also press the full throttle key (default key - shift). Instead of shifting through the gears automatically like the up arrow key, your car will go to redline (pedal to the metal) for as long as you hold the full throttle key. When you release it your vehicle will shift up to the next gear. This technique will allow you quicker starts, and for some cars will offer endless fun and entertainment (think Dragster).