Exactly that – they’re routes with too much car traffic. Usually cycle.travel gives an uplift to roads/paths that are part of a long-distance route. In Europe this largely works… in the US not so much.

The differences are a bit long to list here, but basically, cycle.travel is more cautious when applying an uplift to the USBRS system, the East Coast Greenway, and a number of state bike routes. (I remember cycling in New York State a few years back and the section on NY Bicycle Route 32 was genuinely the worst road of the holiday!) There’s also an entire block on any uplift for USBRS 90/90A because the notion that roads like this make for an appealing bike route is just nuts.

Great, that's what I thought.  It is sad that so many US routes are aspirational.

I live in North Carolina in the USA, along the Adventure Cycling Association's Atlantic Coast Route, and it is pretty sketchy along the route near me. I host quite a few Warmshowers guest and let them know that I don't cycle the route, but there's really no other option. Good news though, there is some better cycling infrastructure in the works for here. 

There was an interesting comment on Reddit a couple of years back:

“I used to work at Adventure Cycling for the team that works with states to enact USBRS routes. Although ACA advocates and tries its best to lobby for safe routes, ultimately it's up to the state Departments of transportation who have their own agendas. Some love the idea and follow existing ACA routes, some think designating routes opens the state for liability so they avoid it (I.e. Colorado...). Some DOTs like/encourage Bicycle travel but had inept route planners who were coerced to route by POI's designated by political/economic interests.”

I guess that goes some way to explaining why the USBRS is substandard in many areas. What I never quite understand is that when there’s a choice between a busy road (with no shoulder) and a quiet county road, the USBRS follows the busy road. In some cases – e.g. USBRS 50 west of Indianapolis – it follows a busy road in preference to a traffic-free bike trail. 

I recall arriving is the U.S. and getting quite the shock at the standard of "bike route". In my innocence, I thought it was a case of simply pointing my bike in the right direction. Oh, foolish, foolish me! Highway 17 in the Carolinas still gives me nightmares! CT saved my ass!

Later, heading cross country, CT was my primary planner and it was far, far superior to the Atlantic Coast route. 

The older I get, the more sceptical I become of "official" bike routes. Too many are designed "by committee" with various different objectives as noted above. Hell, get two bike riders together and ask them for the best way from A to B and you could get three answers! 

Here, in Spain, some of the stories I have come across about the creation/variation in parts of the many, many Camino (Pilgrimage) routes around the country are hilarious! Local farmer makes a fool of himself at the local fiesta, falls out with the townspeople so denies access to his lands, forcing wandering pilgrims to avoid the town. 

I've learned that when CT doesn't want to follow an "official route" there's normally a pretty good reason!  

US 17 in the Carolinas is a bit of a cause celebre! It absolutely astounds me that was chosen in preference to a quieter inland route.

I just planned a route and noticed that the Mississippi River Trail is still being favored as a long distance route in MN and WI.  I think large parts of it are too busy to be favored, sadly.

That’s a helpful observation – thanks. I’ll look at adding it to the ‘cautious’ list with the ECG and similar routes.