A River Road (kbc) or Valley Road / Valley Type Road (kbc) is a roadway or route that runs through the valley of a relatively large natural waterway, using the valley as a means to maintain a fairly level and direct route.
To meet this designation, the river valley should be large enough, and be differentiated enough from the surrounding terrain, so that the valley has a distinctive advantage as a route - e.g., a mature-stage valley, where the valley is more than about 1/4 mile wide, has distinctive valley walls, and fairly dissected uplands beyond. Streams in valleys this size also tend to be navigable for a canoe, at the minimum. Two basic variants exist, the Bank Route and Terrace Route. Because of the clearer physical geography in a matre valley system, this type family tends to be easier to determine typology than upland routes.
Most(?) Valley Routes are Bluffside...and by nature, parallel to the waterway and valley. (An exception is the iffy [Transverse Sprint] Route Type.)
Exemplia Gratia:
The Bank Route Type (kbc) runs on the valley floor / valley flat immediately along the river / stream / waterway, as much as possible abutting the riverbank. It stays as close as possible to the river without running through frequently flooded areas, sloughs, outwash etc. It swerves inland to cross tributaries at ideal locations, where a tributary's bed is stable and not too wide. A natural levee along the bank, however slight, is an ideal location. This placement is probably due to two concerns:
Exemplia Gratia:
The Terrace Route Type (kbc) runs parallel to the river and the valley's course, but usually at a distance from the river and on the less-frequently flooded terraces. It also usually runs along a terrace bluff, on the upper edge (q.v. Bluff Route or Bluff Edge / Terrace Edge). The typical variation is the Mid-Valley Route.
The Mid-Valley Terrace Route Subtype (kbc) runs through the valley floor usually at or near the mid point between the waterway and the valley wall. A mid-point position places transportation in a central position in the tillable land, equalizing the distance to the far ends of the fields at the waterway and valley walls. The mid-point may be the ideal position that compromises being as close as possible to the waterway, while avoiding many floods. As such it is usually on the upper edge of a middle or upper valley terrace.
It may also avoid sloughs, deltas and swampy areas that are close to the valley walls. It may be more direct since the terrain is smoother than the valley wall, and less amorphous than the river bank. A mid-point placement may also be on the tangent in a curve of the valley, i.e. the shortest route from one stream bend to the next.
Exemplia Gratia:Ideal crossing points or fords on a meandering river may be where the river has a straight stretch running perpendicular across the valley, and the Mid-Valley route road placement compensates for that.
The Break-of-Slope Route Type (kbc) runs at the change of slope between the level valley floor and steeper valley walls. Its placement can be seen two ways:
Historically, the value of tillable land generally outweighed a level, easily maintained route, and thus some Break-of-Slope Route roads are more on the slope than the terrace. The results are swerving routes, cuts into toe slopes, fills across tributary valleys and gulleys, outwash cones and meltwater invading the roadway, and short steep rises and dips. Most Valley Roads in small valleys tend to be this type since the tillable land is at even more of a premium than in a larger valley.
Exemplia Gratia:
The Transverse Sprint Route Type runs perpendicular to the valley, within the valley. It is usually a connector between parallel Valley Routes, such as a Bankside Route and a Break-of-Slope Route.
This category may not belong in the Valley Route Supertype, since it is diametrically different from the other Valley Route types (other than its location in a valley). It is not quite a route element, since examples tend to be longer than a stone's throw...
Exemplia Gratia:
The Bluff Edge / Bluffside Route runs atop high upper terraces, usually (in South Central Ohio) on Wisconsinan-age ground moraines along or in major valleys, or Illinoan-age glacial outwash terraces. The route tends to be along the edge of the bluff / highbank, but it need not be there.
[Is this an Upland Route Type or Valley Route Type? Is it both and neither, transitional, and thus deserves its own Type? = upper BOS (vs. lower BOS?) median between Valley & Upland Routes?]
Exemplia Gratia: