Part 40 (1/2)

Down-Time Knowledge: Medieval And Renaissance Treatises

The modernEncyclopedia Britannica briefly mentions the work of Guido Toglietta (1585) and Thomas Procter (1607). Toglietta (1585) described a pavement system based on broken stone; EB characterizes it as an improvement on the Roman structure, but provides no further details. Forbes credits Toglietta with the modern-sounding conceptualization of the wheel as the ”destructor” and the road as the ”resister.” Toglietta ”describes the construction of cobble pavements, but favors a foundation of gravel carrying a road surface of stone, sand and mortar.” Preferably, this surface is two inches thick. (Forbes; Borth 64).

Procter (1607) auth.o.r.ed the first English language text on highway construction. EB doesn't state the t.i.tle, but I suspect that our English correspondents will know it under the name ”A profitable worke concerning the mending of highways.”

Other treatise writers will become known to us only through consultation with down-time scholars.

These authors would include Andreas Palladio (15181580), Vincenzo Scamozzi (15521616), and Castelli (15771644). From Forbes' brief commentary, it doesn't seem likely that they will do more than help us persuade the down-timers that drainage control is important.

Up-Time Knowledge: Roadbuilding Innovations from 17501850

In1632 , Mike Stearns announced one of Grantville's strategies for survival: ”Gear down, gear down.

Use our modern technology, while it lasts, to build a nineteenth-century industrial base.”

Amazing improvements were made in roadbuilding technology during the period 17501850, and the USE can readily exploit them. Before then, when roads fell into disrepair, rulers blamed it on the wagoners, and placed onerous restrictions on loads, wheel dimensions, and so forth. Nineteenth-century builders, notably John McAdam, urged that roads should be made to suit the vehicles, not the other way around (Reader, 131).

The modern Encyclopedia Britannica presents cross-sections of roads as designed by Pierre Tresaguet (17161794), Thomas Telford (17571834), and John McAdam (17561836). The overview which follows is based closely on that provided by EB, and leaves out some important details which are covered later.

Tresaguet's andTelford 's roads were what you might term ”Roman Lite.” Tresaguet's lowest course, eight inches thick, was of uniform stones set edgewise and packed together. He then laid two-inch thick layer of ”walnut-sized” stones, followed by a one inch thick layer of smaller rocks.

Telford's lowest course, like Tresaguet's, was of set stone (seven inches thick according to EB). This was known to later builders as the ”Telfordbase,” although the EB makes it sound quite similar to that of Tresaguet. Above this came another seven inches of broken stone, the fragments being not more than two inches in size. This was capped by a one inch layer of gravel.

McAdam abandoned theTelford base, and indeed all reliance on set stone, and instead relied exclusively on eight inches or more of broken stone. He allowed the rocks to be compacted by traffic.

McAdam's methods were so successful that the compacted broken stone road is known as ”macadam.”

Macadam is a great road surface for horse-drawn traffic, but it is not well suited, without modification, to automobiles. We will consider the design of macadam roads in more detail in a later section.

The first European asphalt and concrete roads appeared during the end of the century in question, but they did not come into prominence until automotive traffic forced their adoption.

Road Design: Route

Ideally, roads would be nearly straight and nearly flat, while quick and cheap to construct. Unfortunately, the landscape usually doesn't cooperate. If the straight line path encounters a hill, the builder has three choices: ascend and descend it, curve around it, or cut (or even tunnel) through it. Departures from linearity may also be desirable in order to avoid a stream or marsh, or to follow a coastline, or to cross a river at a more favorable point for fording or bridging it.

Sometimes there was both a ”high road” and a ”low road” connecting two points, the high road being used when the lower one was too soggy to be traversed (Hulbert, 4445).

Roman road engineers showed a predilection for the ”military crest”: a road just below the crest of the hill, on the slope facing away from the frontier, so as to conceal troop movements from the enemy.

(Chevallier 89).

Road Design: Drainage

Highway engineers say that the three most important aspects of road design are drainage, drainage and drainage. (U.Texas , I:45). Standing water turns earth into mud, of course.

Drainage typically involves such expedients as raising the road, road grading and camber (see below), longitudinal ditches (or gutters), culverts (so water runs beneath the road rather than over it), and subsurface transverse drainage pipes. (The latter were used byTelford , see Smiles 429.) The drainage ditches should themselves be graded, so they are self-cleaning (U. Texas, 7), and it may be necessary to have them feed into a containment pond of some kind if the road is subject to heavy rainfall.

Roadbuilding Methods: Crossing Marshy Ground

Hilaire Belloc opines that an extensive marsh is actually a much greater obstacle to overland movement, unaided by roadwork, than are forests, hills or even rivers. (Belloc, 14).

InBelgium ,Holland , andLower Germany , log roads have been used in swampy areas since 2500 B.C.

(Von Hagen 178). American pioneers cut down trees of similar length and laid them in the direction of travel. The logs could be used whole, or split in half. (Hulbert 4851, Luedtke) The1911 Encyclopedia Britannicacomments drily, ”this is ridiculed as a 'corduroy road,' but it is better than the swamp.” (A suitable saying would have been, ”better logs than bogs.”) Instead of laying just one set of logs, the corduroy road can have two layers, for example, transverse logs over longitudinal stringers. (Hindley, 1112; Von Hagen, 178, Modern EB). The modern American military has also built heavy corduroy roads, with three layers of crossed logs. (FM 5-436, Chap. 14).

Pegs can be used, at intervals, to connect the layers. The purpose of the additional layers is not to increase the load rating, but to make sure that the surface doesn't sink below the mud.

The logs can be placed on loose branches, or on fascines (bundles of brushwood), rather than directly on the marshy soil. If timber is not available, one can use fascines by themselves, or together with sapling sleepers and binders. (Id.) * * *

In the 1632 Universe, corduroy roads may be laid as access roads for logging operations in heavily forested regions, such as the Thuringerwald . Obviously, the logs are readily available, and the road needs to be maintained only so long as there are still trees left to cut.

The other major use of corduroy roads will be by the military. Corduroy roads were used extensively in the American Civil War. Writing about the siege ofRichmond , Joel Cook said, ”Corduroy roads ran in all directions through the swamps, and every general had his roads leading wherever he wished.” (Cook 273).

Likewise, a study of the Eastern Front in World War II said that ”war could never have been waged in the vast swamp regions ofRussia had they not been made accessible by improvised corduroy roads.”

(CMH).

There are other ways of crossing swamps. Blind Jack Metcalf built roads over bogs by laying down gorse and heather in a criss-cross fas.h.i.+on, then spreading gravel over the bundles. This has aptly been termed ”floating a road.” (Albert, 137; Borth, 85).

Besides using simple corduroy roads, the Romans created elaborate swamp-spanning causeways, called pontes longi (long bridges). The via Mansuerisca inBelgium was structured, from bottom to top, as follows: pilings with crossbeams, longitudinal joists, transverse logs, limestone paving cemented with clay, and finally gravel. (Chevallier 8990).

Road Design: Width

Traffic moves on what is technically termed ”the traveled way” or ”carriageway,” and which may be divided into one or more lanes. The roadway is the entire width of surface on which a vehicle may stand or move, and thus includes both the traveled way and the shoulders (and any median strip). The road is the entire right of way, and thus consists of the roadway and the roadsides, from fence to fence.

Nonetheless, in this section, I will use the term ”road” to mean the ”traveled way.”