You can't avoid the D93 in these parts: it's the artery that feeds all the towns and villages all the way from Saillans in the west to Col de Cabre in the east, and forms a substantial part of the road that goes from the Rhône to Gap and on to Italy. Of course, the geography being as it is in these parts, it shadows both the river Drôme and the railway. But as a cyclist, you'll probably get to know it rather better than either river or railway.
From Die, the only way you'll avoid it completely is if you head straight up to the Vercors plateau. But like it or loathe it, the D93 is the way to access an enormous variety of routes west, south and east. But it can also have its pleasures in its own right.
For a start, it is your archetypal French road: great surface (regularly maintained), often with a decent cycle lane, good views, and gently undulating (until Col de Cabre). Secondly, it is not boring, unlike some dead straight Napoleonic roads. Having said that, it can be gruelling: into a headwind, with rain, tired legs, and if you're in a hurry, it can seem interminable: at those times, you've just got to get your head into the place where you can grind out the miles, with teeth gritted, though I will admit to trying to plan routes that don't end with a 20-mile slog along the D93 into a strong headwind.
And so to the advisory bit of this post. Firstly, road signage, and specifically 'priorité a droite'. The default position in Framce is that you give priority at any junction to the road on your right, even if it's a small street joining a bigger one. This will often have a warning 'X' sign. However, this default can be overridden either with a sign giving priority at a specific junction to the 'main road', or by a general cancelling of PaD, signalled by a large yellow diamond. The yellow diamond with a line through re-establishes PaD. (See photos for examples of these signs.) It's not really as complicated as it sounds: most main roads outside of towns and villages aren't PaD, and if you're unsure at a specific junction, just take care!
Lastly, (with reference to the D93): French drivers. French drivers in these parts tend to drive fast, and many will tailgate and overtake other cars as if they are at Le Mans. That said, the vast majority are respectful of cyclists, and you won't suffer any punishment passes.
However, at the same time, most will assume that the D93 (and roads like it) are at all times wide enough for two cars AND a bike, so don't be surprised to be overtaken in places where in Britain the car would hold back. And very occasionally you'll find a car overtaking towards you, and you'll think that they haven't seen you, or reckon you only need 2ft. And lastly, you might see the advisory signs saying "Je dépasse 1.5m", to warn drivers to give cyclists 5ft of clearance: most do, but if they pass you at 60mph, 5ft doesn't feel like very much. The advisory cycle lanes are good, as far as they go, but are prone to disappear without warning in places where you really could do with one. So, for lane usage, my advice would be to cycle in the cycle lane where there is one, and as close to the dotted white line as is safe, when there isn't a lane: I don't think French drivers have heard of 'primary position', and if they have, it's up there with philosophical debate with Satre and existentialism. Oh, and do be careful approaching roundabouts: French drivers practise their artistic skills in their vicinity.
However, all that said, I do think it's generally a safe and pleasurable road for cyclists (especially out of the peak weeks of summer); but do keep your wits about you, and look for the pleasant diversions (where they exist) if you're less confident about cycling on main roads, or find it challenging to ride in a straight line.
Me, I like the D93. Most of the time.
