B.Carfree we'll just have to agree to disagree with out being disagreeable. Consider this. It is likely that the field limit is because jurisdictions along the route that permit the ride require it. Folks that tag along or poach the ride jeopardize the ride in that regard. Kudos to you for putting on a ride with the help of one other. I'll hazard a guess that you can produce 2 of the 4 aspects you mentioned, no traffic and beautiful scenery well there is plenty of the later and not much of the former on STP considering the region it goes through. I have a somewhat different understanding about what no traffic means living and riding in a rural area with a smaller population than Eugene/Springfield. For most of my rides no traffic means less than one car per mile travelled sometimes even when on the state highways.
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Sir Mark, Knight of Sufferlandria