what is this road surface called? they are 'articulated concrete block' 'acb's'

We were out hiking in the Buffalo National Forest to a favorite creek.
This gravel road runs through an edge of the forest.
It's used by local community and visitors alike.

The areas with this surface are in a low stretch along a very small creek that must flood the road frequently so I assume it's a method to stabilize the road.

I think it's been there a long time and was once maybe also covered in gravel?

I like how stable and permanent it seems.

Any body know what the method is called and if the blocks are still used?

They look like breeze blocks repurposed as road base.

I have not seen this exact type but it is a permeable road surface. Like you observed, the open cells are filled with stone.

Rather than have an impermeable paved surface that will direct any runoff to the edges, this allows water to reabsorbed through the road surface openings.

You normally see this style in areas prone to flooding or located in a flood zone. Like most coastal and low lying river/creek areas that are in the AE flood zone.

This is a picture of a more modern style very popular for driveways.

Unfortunately, it is more expensive to install than concrete or blacktop but is required in certain areas. About 2x as much as concrete for some styles.

Judith Browning wrote:The areas with this surface are in a low stretch along a very small creek that must flood the road frequently so I assume it's a method to stabilize the road.

That's probably it. I wonder how they maintain it as clean as it is.

I once did a walking path with perforated bricks. It turned into an impossible weedy nightmare.

Douglas, the weedy nightmare you describe is in fact another mode of the second "modern" block that Josh Hoffman posted a picture of.
I have seen that block marketed under the name "TurfStone", and seen it in-situ in a municipal park. The idea being that one can create a hybrid lawn/pavement, that from afar looks like lawn, and will support vehicular traffic. It is permeable, and protects the grass in the cells from compaction or "wagon ruts" from traffic.

thanks for all input!

I've found a similar picture of these blocks used by the
https://en.m.wikipedia.org/wiki/Emergency_Watershed_Protection_Program

The photo is in a pdf that I can't attach but in it they are called 'acb' blocks with no reference to what that stands for.  This sort of work would have been done by the US dept of Agriculture.

My best guess is they were used to stabilize that stretch of road after one of the major floods in this area over the past few decades.

The blocks are very dense and don't seem worn at all.
Steve noticed that there was some sort of weed barrier under the blocks peeking out at the edges.  

found it!
https://www.conteches.com/knowledge-center/archived-pdh-articles/articulated-concrete-block-design/

ACBs provide a flexible option to other erosion countermeasures such as riprap, soil cement, grout-filled mattresses, etc. As they are not intended for slope stabilization, slope stability must be ascertained prior to considering an ACB system. ACB systems are composed of preformed concrete blocks that are interconnected through a combination of form and/or cables. The blocks are able to "articulate" to some degree along their adjoining faces, allowing the system to conform to changes in the subgrade while maintaining the protective cover. Open-cell forms of ACB are also available that allow vegetation to be established, improving stability and aesthetic appeal.

Someones solution to a problem or how to use a load of concrete blocks ...