Road Root is among the most unique road building technologies employed in Terragen space. The creation of this neogen plant marks the single most successful attempt to build living organic roads. The earliest varieties date back to approximately 5192 a.t. The design has been refined many times since then.
The Road Root tree has been geneered to have qualities that enable it to serve as pavement. The trunk is flattened and has been modified to grow parallel to the ground. The dark gray outer bark has increased density in order to stand up to the rigors of supporting vehicular traffic and specialized texture that offers maximum traction. The inner woody layers are spongy and resilient so as to act as shock absorbers. The road surface quickly absorbs any water that hits it, thereby providing for the plant's hydration needs while reducing the risk of hydroplaning. The leaves grow parallel to the stem on either side — each Road Root has only two leaves. The surfaces and inner structures of the leaves are also reinforced, but only enough to stand up to pedestrian traffic (note that "pedestrian" can include beings as massive as Sufants). The chloroplasts contain multiple pigments to allow the plant to use light outside the visible band for photosynthesis. All Road Root can utilize infrared light, and many varieties can use the longer ultraviolet wavelengths as well. As a living organism a Road Root naturally repairs itself when damaged, though severe wounds can kill it. Some varieties have stripes of light-colored wood running parallel to the length of the trunk as lane markers, while others have strips of raised bark that serve as medians.
An individual tree is about 100 meters long and eight meters wide, though some multilane or industrial grades are wider. The leaves are about four meters wide (or more for the wider grades) and the same length as the trunk. Building a road out of Road Root involves planting several trees so that they will grow end-to-end. Immature plants send up runners that send and receive chemical signals; Road Roots naturally seek each other out. This chemotropism allows road segments to join up accurately and can even cause segments to grow around obstacles. Each plant grows along the path of least resistance to the nearest Road Root within its detection range (about 300 meters in still air).
In addition to its role in transportation Road Root can facilitate power generation. Some types of Road Root support an epiphytic variety of Turbine Plant on the outer edges of their trunks and have organic conductors interwoven with their root systems. The wakes of passing vehicles add to the wind that the Turbine Plants convert into electricity, and the Road Root can act as a line for transmitting that power to a city. The most impressive application of Road Root is in terraforming. Transapient engineers sometimes lay out a world's cities and roads before the environment has been made habitable for oxygen breathers. If the planet's atmosphere is rich in carbon dioxide the roads might be laid out in Road Root early in the terraforming process. The trees will then aid in rectifying the atmosphere; a network of living floronic roads has a dizzyingly vast oxygen output.
Road Root is fast growing for a large tree, but it is still the slowest way to make a road. A plant takes over 20 years to grow to maturity (that is, full bark density) even under optimal conditions, and the road isn't safe for use by heavy vehicles until the tree is fully-grown. Builders who are in a hurry must use some other technology to make their roads. As a woody plant Road Root will burn, but the genetic modifications include several for fire resistance. Chemical spills — especially of corrosives and defoliants — are the greatest danger to the road's structural integrity. It is impossible to plant Road Root over an unsuitable surface; the seeds cannot penetrate rock or metal and can't germinate in ground that lacks the proper nutrients. The tree also cannot grow if there is insufficient light for photosynthesis. The advantage of Road Root is that it is self-repairing (which drastically reduces maintenance costs) and long lasting — the lifespan of an individual tree is well over 4,000 years. Of all the living roads that have been planted to date, the only ones that aren't still in service are those that have been destroyed by natural disasters or by the deliberate actions of sophonts.