I've been wondering about this intersection for a while. 

If you don't recognize that by the picture, this is where Guilford, Rural, and Prospect all meet by Sinnissippi to make a 5-way intersection.

Here's the overview, the picture is taken at the arrow:

As you can see, only three (3) directions for the intersection are painted on the road:

Which is a problem, considering there are four options.

I've always assumed that the left lane was for turning left onto Rural or Prospect and the right lane was for turning right onto Rural or Prospect.

Then, I was sitting at the stop sign in the right lane waiting to turn right onto Rural while another vehicle was sitting in the left turn lane waiting for their turn. When it was our turn to go, the car next to me went through the intersection then veered right onto Rural.

I'll draw it for you:

(As always, my artistic talents can be purchased by anyone. Just email me.)

At first, I thought the other car was in the wrong but then I started second-guessing myself. What is the Rockford rule of thumb when it comes to that intersection? Is the right "turn lane" only for the hard right onto Prospect? I didn't grow up around that neighborhood so I'm not sure what people have done in the past.

If you've made it this far into my ramblings, first of all, thank you. If you have any thoughts on my dilemma I'd love to hear from you. If we're lucky, maybe we can start a whole internet fight about it. Those are the best.