Roads are the term given to the portals built by the Eladamri, the ancient and powerful race of Antiquity. The Roads work by folding space, so that two points intersect and form a passage at the intersection.
These passages are bi-directional and depending on how well-tuned the system is, travelers can see the other side with no distortion. Walking through a Road is as simple as stepping through a doorway; the traveler feels absolutely nothing.
Physically, the roads are often described as appearing like a short length of pipe, big enough to admit a large truck. They are twenty-four feet across but only about three feet long (some vary up to 12 feet).
As mentioned, the gates function by folding space so that two points overlap, creating a path between them. Matter is not "broken down and reassembled" by the gate. Whatever passes through it is entirely unaffected.
Though inanimate objects can pass, environmental effects are typically weeded out (such as wind, snow, and rain). This may be taken out later, or limited to gasses.
Radio signals cannot pass through the fold.
Though a fold could be opened between one gate and a second immersed in water, safeguards would stop the water from rushing through.
The Roads can stay 'on' indefinitely as long as power is provided at either end. In one story, a Road has been functioning for years or possibly decades.