The Sandwich Autoroute is a sandwich defined entirely by where it is sold. It is the prepared, wrapped, refrigerated baguette or pain de mie sandwich bought at a motorway service area, and the category is organized around a single constraint: it has to survive hours in a chilled cabinet, be eaten by someone who has no alternative within fifty kilometres, and ask nothing of the buyer except that they be hungry and in transit. Like the casse-croûte, it is a use-category rather than a recipe. What goes in it matters less than the conditions it is built to endure.
The structural logic is the logic of the cold case. The fillings are the ones that hold under refrigeration without separating or weeping into the bread: jambon-beurre, emmental and ham, tuna mayonnaise, chicken and crudités, the cheese-and-vegetable combinations that survive a long chill. The bread is the variable that decides everything, and it is the part the format fights hardest. A baguette is at its best within a few minutes of leaving the oven and starts losing its crust within the hour; sealed in film and held cold for most of a day, it goes soft, the crumb damp from the condensation that collects inside the wrapper, the crust gone leathery rather than crisp. Pain de mie holds up better under these conditions precisely because it never had a crust to lose. Everything good about a fresh boulangerie sandwich is the first thing the autoroute format takes away.
The honest assessment is that this sandwich is judged by a fairer standard than the one applied to a counter-made baguette. It is not trying to be the jambon-beurre done well; it is trying to be edible at the third hour of a drive, and on those terms the better examples succeed. The test is narrow: is the bread still intact enough to hold together, is the filling fresh rather than tired, is the acid still present in the tuna or the mustard still sharp on the ham. A good one clears that bar. A bad one is the sandwich that has been in the cabinet since the morning before.
Variations are mostly variations of the filling within the same packaging logic, because the packaging is the fixed term. The reliable choices are the ones that fail gracefully when cold and damp: ham and butter, ham and cheese, tuna mayonnaise, chicken crudités. The unreliable ones are anything that depended on a crisp crust or a warm component to work. It sits with the place-named and context-defined builds the catalog groups under Regional Specialty Sandwiches, and its specific contribution is the clearest case of a sandwich whose identity comes from its point of sale rather than its ingredients: defined not by what is in it but by the cold cabinet it had to survive.