This is almost certainly The Highwayman. It was another cheesy Glen Larson series from the late 1980s or so, and depicted two quasi-law enforcement officers who drove trailer trucks that (I kid you not) could convert into helicopters. One of them had this ridiculous Australian accent, but I am uncertain if this was just acting or if he was someone famous from that continent or whatever.

I don't think it lasted a full season.

Here is an image I dug up on Google to confirm it:

Yet another possibility:

This is the Overlander from Terrahawks. It's function is:

an automated all-terrain vehicle similar to a rail-free train with multiple, articulated sections that brings supplies to Hawknest. - (Wikipedia)

This image is from David Sisson's page - a man who restored the original model.

In your question, you mention multiple sections, which the Overlander had. And you mention mountainous terrain - which was exactly the terrain on which the Overlander drove.

See if the vehicle in this video looks familiar:

I think you might have a few shows mixed up but I believe I have your answer. I believe that you are referring to the second season of The Highwayman where they added the actor Mark Alexander "Jacko" Jackson who was a former Australian rules football player.

He had a different-styled (1/2-height) tractor that could separate, unlike the tractor that actor, Sam Jones drove that had a helicopter that separated. Here is a photo of Jacko's tractor-trailer:

Could you be thinking of Damnation Alley? Although produced and released as a theatrical movie, it made its way to TV fairly quickly. IIRC, the TV version was broadcast in two parts, making it feel like a mini-series.

Practically another star of the show, the "Landmaster" was a custom-built articulated vehicle with a very unique wheel arrangement - the three-wheel clusters could rotate to climb over large obstacles. The Landmaster was actually built full-scale and driveable, having a working drivetrain.

As for the "specialized sections", could you be thinking of the movie The Core?

Sounds like Genesis II and/or Planet Earth. These Gene Roddenberry TV movies involved a train system and the character name Dylan Hunt.

Supertrain.

Supertrain is an American television drama/adventure series that ran on NBC from February 7 to May 5, 1979. Nine episodes were made, including a 2-hour pilot episode.