How to make the line like this

When a graphic looks similar to a basic shape like that running track does, it’s often faster to start with a basic shape and edit from there. The running track is just a variation on an ellipse. The demo below shows these steps: 

1. Draw a circular ellipse with the stroke color set to the running track color, and no fill. 

2. Select the circle and choose the command Edit > Copy, then choose Edit > Paste in Front (or Paste in Back). 

3. Choose Edit > Expand, and expand the strokes so that they become filled “donut” shapes instead. 

4. Use the Scale tool to scale down the Height dimension. 

5. Use standard path editing techniques to refine the path shapes as needed. I used the Direct Selection tool and arrow-key nudging to move down the top points on the paths so that the top part of the track is thinner, more like the image you attached. 

6. (Not shown) If you want, cut off any parts you don’t want. 

Illustrator running track kan_8437 Scale tool.gif

For a slightly different perspective, in step 4 use the 3D and Materials panel instead. Enable the Plane option, and set the X axis to a positive value (with Y and Z set to zero).