measurements

(3)    1 acre = 43,560 ft^2 * 144 in^2 /1 ft^2   = 6,272,640 in^2

So 18 acres = 112,907,520 in^2

So the linear scale of the map  =   √1000 : √112,907,520  

So....the actual length of the street will be

15cm * √ [112,907,520 / 1000]  ≈ 5040 cm  ≈ 50.4m

Thank you Chris