I think GP probably was talking about using the shoulder. However, keep in mind that both merging on to the interstate, and city driving are significantly more

I think GP probably was talking about using the shoulder. However, keep in mind that both merging on to the interstate, and city driving are significantly more dangerous than interstate driving. Combine that with the fact that calling to give an ETA is a lot less focus-consuming that most calls, and it is plausible that staying on the interstate is safer.