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All Roads Lead. . . .

Written by Iver P. Cooper

A seventeenth-century visitor might well think that all roads lead to Grantville, not Rome, because down-time roads pale by comparison. "Captain Gars," riding on Route 250, noted its "perfect flatness," and considered it to be "the finest road he had ever seen in his life." (1632, Chap. 57). Rebecca Abrabanel likewise was amazed by the "incredible perfection" of the first up-time road she saw (1632, Chap. 5).

Those roads give Grantville a tremendous strategic military advantage, a force multiplier. "Moses and Samuel [Abrabanel] soon realized that the striking power of the Americans, dependent as it was on their dazzling motor vehicles, was somewhat limited in range. But anywhere within reach of the rapidly expanding network of roads surrounding Grantville, they had little doubt that the Americans could shatter any but Europe's largest armies."

Highways are also important economically. Adam Smith wrote: "Good roads . . . by diminishing the expense of carriage, put the remote parts of the country upon a level with those in the neighborhood of a town. They are upon that account the greatest of all improvements." (EB).

It should be noted that in the early seventeenth century, long-distance overland travel is mostly by packhorse or packmule, not by wagon, because of the poor quality of the highways.

Not everyone will be in favor of improving roads. Innkeepers may fear that travelers will pass their hotel by and go on to the next town. Landowners in some parts of Europe have the right to collect whatever falls from a wagon onto the road, and therefore are perfectly happy to see them overturn. (Forbes, 524) They may also not like to see the central authority exercised more vigorously in their locale, thanks to the improved access.

What roads exist may deteriorate as a result of weather conditions, heavy traffic, and neighbors who figure that it is easier to mine stone from the road than from a distant outcrop. And if the road nonetheless attracts business, then that will in turn attract highwaymen to prey upon travelers.

Up-Time Resources

Grantville is based on the town of Mannington, West Virginia. That is one of four states in which there is no county or township ownership of highways. Hence, the West Virginia Department of Transportation is responsible for the maintenance of over 91% of the public roads in the state. ("West Virginia Highways") The District 4 headquarters is in Clarksburg, and there is a "superintendent" for Marion County. The history section of the City of Mannington website notes that "a WV Department of Transportation garage is located in Mannington which assures that our highways are the first to be taken care of during bad weather." For what is in that garage, see the "Road Construction Equipment" section.

However, the city of Mannington also has a Street/Water Superintendent, and presumably a street crew, responsible for the public roads not under state control.

The Grid indicates that Grantville has a "Streets and Roads Department," with eleven up-time employees. It is possible that most of these were originally employees of the WVDOT garage, but were quickly incorporated into the municipal government shortly after the RoF.

Of the "S&R" up-timers, two are listed as "heavy equipment operators," and another two as trainees. Then we have a dump truck driver, a maintenance scheduler, an equipment maintenance manager, a retired road maintenance man, a street foreman, and a record keeper (and an eleventh employee whose position is not stated).

Another six up-timers are listed as former employees of the state highway department.

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The West Virginia Division of Highways classifies state roads by surface type as follows: (A) primitive, (B) unimproved, (C) graded and drained, (D) soil surfaced, (E) gravel or stone, (F) bituminous surface treated, (G) mixed bituminous, (H) bituminous penetration, (I) asphaltic concrete, (J) concrete and (K) brick (see Roadbuilding Addendum, Appendix 1 for definitions). I have identified types A, B, C, D, and E, as well as paved roads representing one or more of types F–H, in the vicinity of Mannington, West Virginia (list of roads in Appendix 2). These roads presumably have Grantville equivalents.

According to the map in the 1632 RPG Sourcebook, twenty-one roads were cut by the Ring of Fire. Some of these will, coincidentally, be readily linkable to the surrounding German road network. Others will lead into the middle of nowhere. The latter roads may nonetheless serve a useful purpose; modern pavement structure can be studied there.

If these "orphan" roads don't include all of the important road types, then some judicious trench-digging (and subsequent repair) may be helpful for teaching roadbuilding and repair techniques to down-time apprentices.

Canon only identifies one up-time highway as being active in post-RoF Grantville. Route 250 runs by the high school, and in its vicinity parallels Buffalo Creek. It is described as a "well-built two lane highway," surfaced with asphalt, on which it is possible to drive up to fifty miles an hour.(1632, Chap. 2).

Named Grantville streets in Canon include Main (Goodlett, "The Merino Problem," 1634: The Ram Rebellion), Turnbull (Mackey, "The Essen Steel Chronicles, Part 1: Crucibellus," Grantville Gazette, Volume 7), Clarksburg (home of the Inn of the Maddened Queen)(Id.), and High Street (government offices)(DeMarce, "In the Night, All Hats Are Grey," 1634: The Ram Rebellion).

Several down-time roads have been given "official status." According to canon, that means that they are "invariably widened and properly graded. Graveled too, more often than not." "Route 26" is a north-south road passing just west of Eisenach. Two miles to the north of the town, it is crossed by "Route 4" (1632 chap. 52). We also know that the road from Grantville to the (fictional) Imperial City of Badenburg has been improved. (Huff, "God's Gifts," Grantville Gazette, Volume 2). As of Eddie's trip, "the main road to Magdeburg was slated for improvement as an urgent priority," but had yet to undergo its makeover. (Weber, "In the Navy," Ring of Fire).

Brother Johann (Wood Hughes, "Hell Fighters," Grantville Gazette, Volume 3) crossed the Alps, and eventually took a road "down the Elbe River Valley towards where the Salle River joins its flow. There, he saw a road construction machine in action (it had a scoop on an articulated arm). "The road, from that point, became noticeably more level. It had a layer of crushed rock which had been packed in some way. Where washes had been there were now metal pipes to allow the water flow to go under the roadbed."

That road fed into the "'American road' (presumably the extension of Route 250 beyond the RoF) along the north shore of the Schwarza River."

I don't want to spoil Virginia DeMarce's story "Bypass Surgery" (1634: The Ram Rebellion) for those who haven't read it yet. So let's just say that roads play a prominent role in it.

***

The WVDOT garage, and perhaps also Grantville City Hall, should have copies of at least some of the WVDOT manuals (possibilities include the Construction Manual, the Standard Details Books, and Standard Specifications—Roads and Bridges).

They may also have some of the publications of the American Association of State Highway and Transportation Officials (AASHTO). Many states base their highway design manual on the AASHTO "Green Book."

In the Grantville school and public libraries, most of the information on roadbuilding is in the encyclopedias. However, the public library does have a copy of Searight's The Old Pike: An Illustrated Narrative of the National Road.

***

It is clear that the S&R department is training down-timers to work on road crews. However, S&R is geared toward maintenance of existing roads, not design and construction of new ones. If highways are to be designed scientifically, someone will need to create the appropriate educational institutions. These can be specialized (in OTL, the world's first institute for road and bridge design was established in France, in 1747, see Hindley 75), or a part of a larger university.

According to the Grid, several individuals hold a bachelor's degree in Civil Engineering: Jere Haygood, Kimberly Jane (Collins) Glazer, Mason Chaffin, Derek Modi, Allen Lydick , Edward Monroe, Garland Franklin, Jacob Bruner, Ronaldus "Ron" Koch, and Farris Clinter; Mason Chaffin is the Grantville surveyor, in fact. While these individuals are going to be devoting quite a bit of their time to military projects, we can hope that on a rotating basis, they can teach civil engineering students in Magdeburg, Jena or Grantville.

West Virginia University's undergraduate civil engineering curriculum requires students to take courses in Engineering Design, Engineering Economics, Thermodynamics, Surveying and Computer-Aided Design, Statics, Dynamics, Mechanics of Materials, Fluid Mechanics, Materials, Structural Analysis, Foundations Engineering or Earthwork Design, Concrete, Steel or Timber Design, Hydrotechnical Engineering, Soil Mechanics, and Transportation Engineering. The latter is described as "Integrated transportation systems from the standpoint of assembly, haul, and distribution means. Analysis of transport equipment and traveled way. Power requirements, speed, stopping, capacity, economics, route location. Future technological developments and innovations."

The students are also required to take two 400-level civil engineering electives. It is possible that one of them has taken CE 431, Highway Engineering, as an elective: "Highway administration, economics, and finance; planning and design; subgrade soils and drainage; construction and maintenance. Design of a highway. Center line and grade line projections, earthwork, and cost estimates."

We can assume that all of these individuals have kept their course textbooks. (I still have my chemistry books from the early seventies.)

Common Knowledge: Roman Roads

For the seventeenth-century European, the "gold standard" for highways were certainly the Via Appia, Via Flamina, and other Roman roads. According to Nicholas Bergier (1567–1623), European peasants thought they were "the work of demons, giants, and fairies using magic arts."

Bergier was a French lawyer, living in the ancient town of Rheims (Roman Durocortorum). He pioneered the study of the Roman roads, eventually writing the influential treatise Histoire des Grands Chemins de l'Empire Romain (1622) at the command of Louis XIII. (Von Hagen, 14–15). It went through many editions, and copies are certainly available in down-time private libraries in the USE.

USE engineers can see the Roman roads for themselves, but only if they are willing to travel a bit. Thanks to the Teutonic victory at Teutobergerwald ("Varus, give back my legions!"), the Romans did not penetrate deeply into Germany. The Romans fortified the Rhine River, and Roman roads connected the garrisons along the west bank. Another Roman road ran along the Danube from Switzerland to the Danube delta, first along the north bank and then (crossing the river north of Munich) along the south one. (Von Hagen, 18–19) This is shown clearly on a map in the modern Encyclopedia Britannica.

The most elaborate form of the Roman road was the via munita, distinguished by a convex surface (dorsum) of rectangular or polygonal blocks of hard stone (such as lava). The via glareata had a graveled surface, and the via terrena, one merely of leveled earth. The surface used depended on both the importance of the road, and on the availability of suitable local materials.

While the via munita structure may sound ideal, it actually requires a great deal of maintenance to handle wagons. Once one block sinks a little more than the others, perhaps as a result of settlement of the underlying soil, it will tend to be driven deeper by the shock of each passing wagon falling onto it. Hence, wheeled traffic demanded a softer pavement, such as one of earth or broken stone, which could be smoothed out readily. (Gregory 123–4).

The early imperial poet Publius Papinius Statius described the construction of the Via Domitiana in his poem "Silvae." (The first medieval edition was published in 1472.) According to Statius, the workers dug two parallel, widely separated, drainage ditches (sulci) and heaped the excavated material in-between (forming the gremium or agger). Curbstones were laid between the ditches and the elevated roadbed, and the latter was flattened. The other road layers were then laid on top of the soil.

There is some dispute as to the exact nature of those layers. Based, for example, on Vitruvius' description of pavement construction in De Architectura, Bergier believed that beneath the road surface were three other layers. (Ramsay; Gregory 66). The modern Encyclopedia Britannica accepts (without proper credit) Bergier's analysis, and describes the four courses, from top to bottom, as follows:

summa dorsum: large stone slabs at least six inches deep.

nucleus: about twelve inches thick, concrete made from small gravel and coarse sand (other sources say that this was made from broken pottery or bricks, cemented with lime).

rudus: about nine inches thick, concrete made from stones under two inches in size (other sources say that these stones were larger than those of the nucleus).

statumen: ten to twenty-four inches thick, stones at least two inches in size (other sources say hand size or larger).

However, some later writers have questioned whether the road structure was usually so elaborate (Von Hagen, 35; Chevalier, 86). In Britain, at least, stone surfacing was rare, and roads were made of gravel, flint, chalk, loam, and occasionally, as an underlayer, sandstone, limestone or iron slag. (Margary, 500–1).

Roman roads were elevated, sometimes as much as four or five feet over the native ground level. (Margary 20) This seems higher than necessary for drainage, and it has been speculated that it rendered marching troops less liable to attack—enemy forces could be seen at a distance, and would also have to attack uphill. The imperial highways were also more direct than what economics alone would dictate, and this too, was probably for military reasons, as again it reduced the risk of ambush. (Belloc, 134–7; Hindley, 41).

Down-Time Knowledge: Medieval and Renaissance Treatises

The modern Encyclopedia 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) authored the first English language text on highway construction. EB doesn't state the title, 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 (1518–1580), Vincenzo Scamozzi (1552–1616), and Castelli (1577–1644). 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 1750–1850

In 1632, 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 1750–1850, 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 (1716–1794), Thomas Telford (1757–1834), and John McAdam (1756–1836). The overview which follows is based closely on that provided by EB, and leaves out some important details which are covered later.

Tresaguet's and Telford'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 "Telford base," 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 the Telford 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, 44–45).

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 by Telford, 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).

In Belgium, Holland, and Lower 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 48–51, Luedtke)

The 1911 Encyclopedia Britannica comments 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, 11–12; 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.)

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In the 1632 Universe, corduroy roads may be laid as access roads for logging operations in heavily forested regions, such as the Thüringerwald . 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 of Richmond, 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 of Russia had they not been made accessible by improvised corduroy roads." (CMH)

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There are other ways of crossing swamps. Blind Jack Metcalf built roads over bogs by laying down gorse and heather in a criss-cross fashion, 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 in Belgium was structured, from bottom to top, as follows: pilings with crossbeams, longitudinal joists, transverse logs, limestone paving cemented with clay, and finally gravel. (Chevallier 89–90).

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."

The necessary width depends on what traffic the road will bear. The Roman roads were ten to thirty feet wide, with the norm being in the fifteen to eighteen feet range. (Hindley 42) Tresaguet and Telford both favored an eighteen foot wide carriage way, but the Cumberland Road in the USA had a twenty foot breadth. (EB)

The 1911 Encyclopedia states that fifteen feet is wide enough to allow the "easy passage of two vehicles;" plainly they are thinking of wagons rather than motor cars. According to the AASHTO "Green Book," the standard lane width for modern automotive traffic is 3.6 meters (twelve feet). However, rural roads can have widths as small as 2.7 meters (nine feet).

"Plank roads" (see below) were often constructed with a single lane, eight feet wide. One lane roads will need to have occasional turn outs to allow vehicles to pass each other.

The USE's roads need to be wide enough to allow the passage of its armored personnel carriers (APCs), which are converted coal trucks.

Road Design: The Ruling Gradient

The ruling gradient is the average vertical grade as one travels along the centerline of the road. The grade is usually expressed, not as so many degrees of slope, but as a ratio of the vertical change to the horizontal one. For example, a grade of 1 in 40, which corresponds to a slope of 1.4 degrees, means that there is a change of one vertical foot as you travel 40 horizontal feet. Prior to 1800, steep grades of 1 in 12 were common on English turnpikes (Reader, 17).

Keeping gradients small makes it easier for draft animals to haul a load, and hence reduces the fuel consumption by automobiles and trucks. It also minimizes brake and tire wear.

If the traffic is moving uphill, then the steeper the gradient, the greater the degree to which the force of gravity is directed in opposition to the uphill movement. In other words, the horse or motor vehicle must lift more of its own weight in order to proceed. If the load is one long ton (2240 pounds), then the "grade resistance" is 22 pounds for a gradient of 1 in 100, 45 for 1 in 50, and 112 for 1 in 20 (Gregory 127).

Downhill movement is of course easier, since gravity is then on your side, but only if the gradient is not so great that a braking force must be exerted to keep control. And, of course, if you are zipping downhill in one direction, that means you will be trudging uphill when you return.

Gradient is an issue for motor traffic, not just horse-drawn wagons. Steep uphill grades reduce speeds, while precipitous downhill ones increase brake wear. Grades also affect tire wear and fuel consumption.

The effect is dependent to some degree on the weight of the vehicle. The Encyclopedia Americana says that "a grade of 6% or 7% has little effect on passenger-car speeds but greatly slows truck traffic."

It may seem as though the road, ideally, should be perfectly level, but this is not the case. A level road doesn't drain well. The 1911 Encyclopedia says that the minimum ruling gradient should be 1 in 150, and the master road builders of the nineteenth century typically preferred gradients of 1 in 30 or 1 in 40. Their roads rise and fall gradually, rather than remaining level.

The Encyclopedia Americana notes that the crests of hills should be flattened to increase visibility.

Road Design: Elevation and Camber

Elevating the road bed above the ambient ground level helps to reduce the influx of groundwater. This tactic, which dates back to ancient times, is why major roads are called highways.

Again to ease drainage, roads have a convex cross-section, known as "camber." While used by Roman engineers, it was not a universal practice in the seventeenth century.

In 1607, Thomas Procter pointed out that standing water was the bane of roads, and urged general adoption of a convex road surface. Nonetheless, until the mid-nineteenth century, there were experiments with other approaches. The "Ploughman's Road" was horizontal, but elevated and flanked with deep ditches. The "Angular Road" was slanted to one side only. In 1736, R. Phillips urged the merits of a concave road. His theory was that the water would run down the center and carry away loose material. (Albert, 135–8). In 1810, McAdam warned against a road which was "hollow in the middle," but seemed to think that a level road was just fine since "water cannot stand on a level surface." (Reader, 37). Unfortunately, it can.

On the other hand, a steep camber is also undesirable. It makes fast-moving vehicles prone to overturn (Gregory, 131; Forbes, 528, 531), especially as they negotiate curves, and the traffic tends to crowd onto the central portion of the road, causing it to form ruts. (U. Texas, I:6; 1911 EB).

1911 EB generalizes that the usual rise in the center is one-fortieth to one-sixtieth of the width. It can be shallower if the surface is waterproof; Gregory (131) teaches 1 in 48 for macadam, 1 in 60 for tar macadam, 1 in 72 to 1 in 96 for asphalt, and 1 in 80 to 1 in 132 for concrete.

Road Design: Friction

Friction is both bane and boon for traffic. Up to a point, the lower the friction the better; the greater a load that a draft horse can pull, the less fuel an automobile must consume to cover a particular distance. However, on a frictionless surface, an object at rest would remain so, its wheels spinning uselessly, and one in motion could not stop.

Table 2.2.3 in the Transportation Cost FAQ on www.1632.org sets forth the load which a single draft animal can haul, in a vehicle with a particular type of tire, on a level road of a particular surface type, as a multiple of the pull exerted by the animal.

Road Design: Unsurfaced Roads

Construction of a primitive road (WVDOT type A) just means clearing a path: cutting back bushes; felling trees and removing their stumps; taking out boulders which block the way.

The next step up (WVDOT type B) is to grade and drain the road.

What the WVDOT calls a type C "soil-surfaced road" is more aptly termed a "stabilized soil road." The native earth can be strong or weak, and more or less susceptible to rainfall and temperature changes. In a stabilized road, this is altered by chemical or physical means.

The 1911 EB says that "in carrying traffic over a clay soil a covering of 3 or 4 in. of coarse sand will entirely prevent the formation of the ruts which would otherwise be cut by the wheels; and if the ground has, already been deeply cut up, a dressing of sand will so alter the condition of the clay that the ridges will be reduced by the traffic, and the ruts filled in." Collier's Encyclopedia notes, more generally, that sand can be added to clay, clay to sand, cement to soil, and oil to soil, all to create a more weather-tolerant road surface. Such hybrid soil roads are very cheap to construct (Oglesby 633; Gillette).

The civil engineers of Grantville may be aware of other stabilization techniques. For example, calcium, magnesium and sodium chloride can be added to soil to make the particles adhere better. (Id.). The modern EB suggests addition of small amounts of lime, portland cement, pozzolana, or bitumen to the top eight to twenty inches of the ground.

Road Design: Surfaced Roads, Generally

Surfaced roads provide a "wearing surface" (also known as the "pavement," the "road metal," the "carpet," and the "surface course") which is in actual contact with the traffic, and provides enough friction for the vehicles to make headway, but not so much as to unduly slow movement.

Pavements are usually classified as rigid (like concrete, mortared brick or fitted stone), flexible (like asphalt, wood, and compacted stone) or granular (like gravel and sand).

Each surface has its unique characteristics in terms of strength, water resistance, friction, and so forth. For example, the modulus of elasticity, a measure of the extent to which a material deflects in response to stress, ranges from 280–300 for asphaltic concrete, to 30–40 for coarse sand. (Kezdi, 255)

The combined rolling and air resistance (the two are hard to separate) experienced by a one ton vehicle traveling 25 mph on pneumatic tires is, on average, 32 pounds for concrete, 35 for sheet asphalt, 38 for grout filled bricks, 34 for wood blocks, 40 for graded and maintained soil, 50 for gravel or firm natural soil, 70 for well packed snow, and 75 for soft natural soil. (Agg, 13).

Road Design: Lanes, Trackways and Road Rails

Sometimes, a road carries both heavy and light traffic. The former may need a pavement which is "overkill" for the latter. One expedient is to have lanes with different road surfaces. For example, American plank roads were sometimes built with just one eight foot wide lane of planks, flanked by a dirt lane. If the traffic justified it, the company built a second plank lane.

It is conceivable that we will build hybrid roads, with both a hard concrete lane for military vehicles, and an asphalt, wood, macadam or stabilized earth lane for horses. Napoleon reportedly favored a "tripartite road" with cobbles for the artillery, a macadam-like surface for the infantry, and an earth road for the cavalry. (Forbes, 536).

The second approach is the trackway; that is, two longitudinal bands of stone, or even steel plate, separated so as to match the wheel spacing on the heavy vehicles intended to use it. Creating the trackway was less expensive than covering the entire width of the road with metal. A double wheel trackway, on which four horses could pull a load of seventeen tons, was in use on the Albany-Schenectady road from 1834 to 1901. (Gregory, 141–2).

The most extreme form of the trackway is the road rail, used typically in mines, which evolved eventually into the modern rail track.

Road Design: Pavement Structure

The native soil and rock underlying a roadbed were once called the "foundation" or "basement," but it is now customary to refer to them as the "subgrade." The term "subgrade" is also used to refer to imported soil (you might use this in building a road across a swamp).

The subgrade needs to be able to support the load. Peat bears a mere 56 pounds per square foot. You can put one to four tons on a square foot of chalk, two to five on one of fine sand, three to seven on clay, four to eight on gravel, and up to eighteen tons on ordinary rock. Clay and chalk are better when dry than when wet, and rock is unpredictable because it can have soft spots and even cracks. (Gregory 129–30). A native foundation which is unreliable will be removed and replaced with an alternative subgrade.

For drainage purposes, the subgrade is usually raised above the original ground level. Before one can build the pavement structure over it, one must be sure that it is stable. Early builders simply allowed the material to settle. However, in modern times, the subgrade is compacted by rollers.

There may be one or more layers separating the surface from the subgrade. These may be called, simply, the "base course" or "the sole." When there are two distinct layers, these may be identified as an upper "base course" and a lower "subbase course," and there can actually be more than two distinct layers. Also, with asphalt surfaces, there can be a thin "binder course" between the asphalt and the base course.

Road Design: Gravel- and Loose Stone-Surfaced Roads

A simple improvement on the basic dirt road is to cover it with gravel. The 1911 EB says, "Smooth rounded gravel is unsuitable for roads unless a large proportion of it is broken, and about an eighth part of ferruginous clay added for binding. Rough pit gravel that will consolidate under the roller may be applied in two or more layers, but each must be of similar composition, or the smaller stuff will work downwards." The recommended foundation is "rough chalk sufficiently rolled to stop the gravel while draining off the surface water."

The Lancaster (Pennsylvania) Turnpike (1794) was hard-surfaced with gravel and broken stone. (WBE)

Road Design: Macadam Roads

Macadam roads ...