I've been broken of shooting the apexes on local freeway exit ramps. For several years I'd entertained myself by taking them at high speed, using every available scrap of the pavement. Then I noticed I was having flats about every six months - sheet metal screws, mostly. After that I stayed out of the marbles near the curb and haven't experience more than a slow leak or two in the past few years. Thankfully, with all but a total tread failure, I can usually limp to the nearest tire shop. I don't trust the cheap OEM jacks that are supplied with today's cars.
Over the years of riding cross country on my bicycle, Lil4X, I've learned the very same lesson: "No matter how wide and smooth the shoulder of the road way is, DO NOT RIDE ON IT!"
I ride just to the left of the "fog line," IN the traffic lane, WITH the flow of traffic. Why, you may ask?
Because I reason, that glass bottles and such, thrown from moving vehicles will crash and break on or near the "fog line" and then scatter forward and out onto the paved shoulder, (where most of my friends ride). They continue to get MORE flats riding there, than I do in my postion.
Safety concerns riding on the edge of traffic. No more than riding on the shoulder. Ride responsible, and predictable. DON't weave back and forth. Traffic can see you IF they want too, and can hit Ya, even on the shoulder. Stay visible.