Speed Ramp is one of the various obstacles in Battle Run. It can be of any various lengths.
When running upon, a Character is granted a speed boost. This boost stacks with most other speed boosts, including Boost, Hoverboard, and other pets that grant a speed boost. The Character must be in direct contact with the ramp, however. If you jump over the ramp, the speed boost starts to fade. That is the way the speed boost works: Instead of it being removed all at once, the speed boost fades over about one and a half seconds, depending on how fast you're going.
Speed Ramp should be used whenever possible: The speed boost is a built in way to beat other racers without the use of weapons. However, you must be careful, as often Speed Ramps will lead into other obstacles such as Spikes and Fire. When using weapons such as Landmine or Goo, it may be a good idea to use them while you are on the ramp, so as to put these traps out for the next character to try and use the ramp.
More information on speed boosts here.