Ramp Car Lab vs. Flat Surface Car Lab

Our class has done 2 car labs in the past few classes.  In the one on a flat surface, the car had a constant speed, velocity, and acceleration.  In the one on a ramp, the velocity, speed, and acceleration all increased more as it went on.  Both have a constant starting position.  The difference between the position graphs was that the one across a flat surface had a linear function since the slope (m/s) was constant.  The ramp car's slopes gradually increased more and more so it resulted in a quadratic function.  What exactly are the slopes in the position graphs for the quadratic? We wrote out what they could be on the board but didn't come upon a definite answer.  They could represent velocity, speed, or acceleration but I think we should all come to an agreement and maybe do another lab with the ramp to go more into depth and be more accurate with our answers.