My best guess would be that the reasons are not the same in the two cases. Insurance companies might have different insurance conditions.

habituellement

English term (edited): heavy / light roads

roads are either heavy or light;

heavy roads are "heavy" as in "heavy duty" - heavy roads are themselves more "heavy" as they use more road-building material [compared to light roads] in order to be able to sustain a traffic of "heavy" vehicles;

https://www.google.co.uk/search?q="routes pour véhicules lou...

IOW what is "heavy" or "light" is the weight of individual vehicles (weight-per-axle) not the volume of traffic/number of vehicles.

"Axle load

The axle load of a wheeled vehicle is the total weight felt by the roadway for all wheels connected to a given axle. Viewed another way, it is the fraction of total vehicle weight resting on a given axle. Axle load is an important design consideration in the engineering of roadways and railways, as both are designed to tolerate a maximum weight-per-axle (axle load); exceeding the maximum rated axle load will cause damage to the roadway or rail tracks. "
https://en.wikipedia.org/wiki/Axle_load

http://www.pavementinteractive.org/article/equivalent-single...

"....

Heavy and Light Roads

The haphazard system, of allowing factories and residences to be mixed together in rural areas as well as in villages and towns, without any discrimination, also makes it difficult, on the one hand, to get wide main thoroughfares where they are required, and, on the other hand, to secure a higher standard of road construction, giving access to areas that should be reserved for manufacturing purposes. The heavy trucks and wagons which use the streets in industrial areas require heavy roads, but, because we do not reserve special areas for manufacturing and other areas for residential purposes, we have either to make our roads too light for manufacturing purposes or too heavy and expensive for residential purposes. Thus in regard to width, length and construction of streets we have to keep up an extravagant standard because we have no proper development plan. It is because of this that the advantage of having wide roads where these are needed for through traffic is often questioned, the plea being that to provide for very wide roads casts too great a burden on the present generation for the benefit of posterity. That plea rests on the erroneous assumption that all roads should be wide and that we do not need to vary and regulate their width according to the use to which they have to be put. Under a proper scheme roads should not, as a whole, occupy a greater superficial area than they do now, but, complementary to the narrow residential street fringed with deep front gardens or the narrow farm lane, there would be the wide main artery. ..."
http://archive.org/stream/ruralplanningdev00adam/ruralplanni...