I write my comments as a "Rider".
You said the right thing, if it is safer to overtake at 100 kmh
when the cars are moving at 80 kmh; unfortunately, outside the max
peak hours, most cars are travelling at 100 kmh PLUS along most
expressways.
However, do you think it is much safer overtaking those larger
trucks that are travelling at only 60 kmh on Lane 4 (roads with 4
lanes), or the speeding cars at 100 kmh and more ?
As I have written, the gaps between these large heavy trucks, are
at times more then 200 or even 300 meters, and that should give
anyone enough distance to view the situation up ahead, and "zipped"
between trucks.
Many of the lighter goods vehicles (those 1.5 tons trucks or large
Panel Vans) seldom want to travel behind these lumbering heavy
trucks, which struggle at 60 or 70 kmh on Lane 4, when the 1.5 ton
trucks and panel vans are moving at 80 and even 90kmh or more - on
Lane 3 or 2.
On Lane 1, you will find most cars going at 100 to 120 kmh; with
some occassional retard drivers, doing 80-90 kmh on Lane 1, when
there is no traffic ahead (following the speed limit posted, and
refusing to move to Lane 2 or even Lane 3 or 4), when our bikes,
vans, or cars can go faster.
I find it safer to see the road ahead, when riding near the solid
line between Lane 4 (or 3) and the Road Shoulder, as there is
nothing obstructing my view; and I can zipped by the 60kmh Big
Heavy Trucks, knowing that the vans or light trucks will not be
able to match my 100 - 120 kmh throttle up.
When I see any vehicles (cars, vans, trucks) on the road shoulder
itself. I am more alert to their presence.
Try it on those heavy traffic hours, it is easier to handle the
lumbering trucks on Lane 4 and 3, than the faster responding
cars.on Lane 2 or 1.