It is not clear where or when Cattle Grids emerged as an effective solution to confining stock while allowing wheeled traffic unimpeded access through fences. There are indications that it emerged separately in regions hemispheres apart.
In the UK there were units in place in Victorian and perhaps Georgian times as Country Estates grew in popularity. Tricky to open a gate wearing a crinoline while up to knees in poo! Ask Ian Harvey!
The intervention of an Engineering Genius in the form of Geof Freedman, Chief Civil Engineer of the Forestry Commission was a game changer. The FC used huge numbers of Cattle Grids and he needed to standardise them and reduce the cost for installation. His design is now the Industry Standard. It is modified to deal with different loads. The beauty of this elegant design is its speed of installation – road closed for hours rather than days.
There has been an attempt to offer a “Standard Unit” by IAE but these rely completely on the quality of the concrete works with often dire results. Grids banging as they are crossed are irritating and in time the repeated flexing can made welds fail or members to fail. It is impossible to hold down a grid which does not fit properly onto the concrete.
A novel, (novelty?)approach by Ian Harvey Fabrications is to supply a pre cast concrete base for the units. Laugh – I thought my trousers would never dry!!
You may gather that your guru prefers the Pitless/Drop-in units as they usually work instantly and for a very long time. There are occasions when a conventional unit is the best solution and it can be the cheapest.