Answer: There are 53 new signs are needed.
Explanation:
Since we have given that
Length of section of a highway = 23 miles
At every 0.5 miles in between, new signs will be placed at the beginning.
So, Number of new signs would be

And there is a new sign at the beginning too.
So, the number of new signs would be 52+1= 53.
Hence, there are 53 new signs are needed.