If you see double solid lines on two-ane roadways you should know that

(x_m, y_m) = (\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2})

Explanation:

The Midpoint Formula does the same thing. If one X-value is at 2 and the other X-value is at 8, to find the X-value halfway between them, you add 2+8 and divide by 2 = 5. Your would repeat the process for the Y-values to find the Y-coordinate of the midpoint.