Extra wide shoulders on I-190 Sterling Ma.

[ne11931]

Could someone explain why the shoulders of I-190 from about mile marker eleven to twelve are double the normal size. Also they look like the asphalt is dyed green in some places?
I'll try to post GSV link-

I-190

https://goo.gl/maps/G32UDtWMKgA2

[Duke87]

According to Steve Anderson's site this was done to help prevent road salt from running off into nearby Wachusett Reservoir.

Though I will admit I am not sure exactly how or why that works. Intuitively you would think less impervious surface would be preferable for runoff control, not more.

[cl94]

As stated above, runoff control. If you look closely on GSV, the shoulders are sloped to drains on the inner edge of the green portion. This basically forces all runoff from the expressway to enter the sewer. This also happens at a point around mile 5.