At the icon location is an XL streetlamp with a "Reduce Speed Now" sign. On the back of the sign are 6 characters, some letters, some numbers "ABCDEF". Treat numbers as numbers and letters a numbers using a=1 to z=6.
The cache may be found at N 51 12.(A+B)(D-B)(E+C-A), W 0 34.(B+F-C)(E-D)(D+E+F-A-B-C).