Are you allowed to walk along the highway in Russia? Isn't it very dangerous?
That's the way it is on this course, but in real usage there's no strict difference between 'road' and 'highway'. As well as serving as the broader category which contains 'highway', 'road' also often functions as its synonym. Whether 'road' or 'highway' is the best translation of шоссе in a given sentence is really a matter for the translator's judgement.
Besides that, the word 'highway' is rarely used in British English, so any шоссе which is not wide enough to qualify as a motorway is normally known as simply 'a road' in the UK.
And I got flattened by a truck going 140 KPH. Or I was slowly walking down the highway because I was so stinking drunk I didn't know where I was.
Possibly: I was walking slowly beside the highway. I was walking slowly next to the highway.
Highway is most commonly a high speed road (90KPH+) in US English (the language of this course). A street would have a speed limit of 40 to 60 KPH. A road, likely 60 to 80 KPH. A path, trail, sidewalk or even the shoulder of a road would be most appropriate for walking.
I would never be slowly walking down the highway.
I also think a slow walk is not the same as walking slowly. Placing the adverb in front of the verb in this implies something like an aimless stroll. The adverb after the verb implies walking with purpose but at a slow pace.
This one baffles me.