Chapter 10.

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ROADS, AND THOSE IN TRING.


A BRIEF HISTORY OF ROAD BUILDING.

“The need for surveillance at the peripheries of empire led to the building of 250 miles of new roads in Scotland between 1726 and 1737 ― by the early 19th century, 900 miles of military roads had been built and were maintained by the British state in Scotland ― the first large-scale state road-building programme in Britain . . . . Modern road construction emerged in the military laboratory of Scotland between 1726 and 1773 as a craft known to soldiers and surveyors.”

Roads to Power: Britain Invents the Infrastructure State, Jo Guldi (2012).


EARLY ROAD BUILDING IN BRITAIN.


Origins.

 

Corduroy road.

The earliest of our roads might be described as ‘improved’ tracks.  Some improvement of the natural landscape would have been desirable at fords, and through mountain passes and swamps.  They would have consisted largely of clearing the track of trees and boulders, but as commerce increased the track might be flattened or widened to better accommodate human and animal traffic or, perhaps, sledges. [1]  As a result, by about 5,000 BC tracks developed along ridges in England that avoided the need to cross rivers and marshland.  Where marshland did need to be negotiated, an improvement could be obtained by placing logs perpendicularly across the line of track, perhaps with longitudinal bracing, a type known as a ‘corduroy’ or ‘log’ road. However, while aiding the passage of human traffic, movement in the logs could prove hazardous to horses.


Roman roads.


As discussed in chapter 1, our first roads — that we would recognise as such today — were built by the Romans who required direct all-weather communications to meet the demands of their centralised administration (a form of government not seen again until the late Anglo-Saxon era). Their requirement was to move large masses of troops, supplies and government officials quickly around the country, and to meet this demand they built a network of well engineered roads:

 

“Considering the fact that such works of engineering skill had all to be done by patient manual labour, through a wild and meagrely cultivated island, we can easily see what a vast expenditure of time and effort must have been involved in it.  In some places, great quantities of timber had to be cut down; in others, the ground had to be embanked and drained before it was firm enough to advance upon.  The shallower streams were crossed by paved fords, whose courses were marked by large wooden posts.  The enduring quality of the works, as well as their great extent, left its impress upon the face of England to such a degree, that these roads are the wonder of the engineering world today.”

The Development of Transportation in Modern England, W. T. Jackman (1916).


Generally speaking ― for there was no hard-and-fast rule ― road construction commenced by removing loose earth and excavating a wide trench to a depth at which a foundation was reached that was sufficiently solid to support the road. [2]  Stones were then laid onto the base in strata, each stratum having slaked lime poured onto it to produce a crude form of concrete.  Where stone was plentiful the road surface might be paved with slabs, otherwise crushed stone was used.


Cross-sectional diagram of an idealized Roman road as found in Britain.


The road thus formed, several feet thick, was raised slightly above ground level, its hardened surface being laid with a camber to allow rain water to run off into the drainage ditches.  A kerb prevented the edges breaking up.  In some locations the road was further embanked above the surrounding land to prevent the road bed becoming saturated in wet areas, to maintain the gradient, and to help guard against ambush in violent times. [3]  On wider roads, the strips of ground between the road and the boundary ditches were used by pedestrians.  If shallow, streams and rivers were crossed by paved fords marked out by stakes or, if not, by timber bridges, sometimes laid on masonry piers, but the Romans appear not to have built stone bridges in Britain.  Ferries were used to cross major rivers.


The medieval period.


The road-building principles used by the Romans were not seen again in Britain until the 18th century.  In the meantime our population increased as did the number of settlements and new roads linking them, but as they were not constructed according to civil engineering principles, such as those of the Romans, there is little archaeological evidence of medieval roads outside of towns.

Under Henry VIII, law was enacted for road maintenance.  But the standard at that time and for many years thereafter, was limited to filling in ruts and holes with whatever material came to hand, clearing drains and cutting back overhanging foliage.  All these tasks were performed by parishioners under the supervision of an unskilled member of the parish who had had the misfortune to be appointed ‘surveyor’.
 

By the 17th century, the use of wheeled vehicles was becoming much more common.  In order to reduce the incidence of their wheels cutting ruts into what road surface there was, James I. introduced law that limited the minimum width of vehicle wheels (to lessen wheel pressure); required axletrees to be of different lengths (to ensure the rear wheels passed over a different surface to those at the front); required horses to be tethered abreast, rather than in line (to spread wear from the horses’ hooves); and limited vehicle weight.  Other restrictions were more intricate; for example . . . .
 

“. . . . the several Nails of the Tire or Tires of the Wheels of every Waggon, Wain, Cart, or other such Carriage used or drawn on any Turnpike Road, shall be so countersunk as not to project beyond One Quarter of an Inch above any Part of the Surface of such Tire or Tires;”

Geo. IV., cap 95, RA 19th July 1823.


. . . . transgressors could be fined forty shillings, if the vehicle owner, and twenty shillings if the driver, for every incident.  But the law could have had little effect, for even as late as the 18th century the seasoned traveller Arthur Young (1741-1820) had this to say about the state of a road in Lancashire over which he was obliged to pass:
 

“I know not, in the whole range of language, terms sufficiently expressive to describe this infernal road.  Let me most seriously caution all travellers who may accidentally propose to travel this terrible country, to avoid it as they would the devil; for a thousand to one they break their necks or their limbs by overthrows or breakings down.  They will meet with ruts, which I actually measured, four feet deep, and floating with mud, only from a wet summer; what, therefore, must it be after winter?”


And similar stories abound. However, the 18th Century was to produce four civil engineers ― each of whom arrived in that embryonic profession rather by accident ― who between them returned road-engineering to a standard last attained by the Romans.


――――♦――――


THE BEGINNING OF MODERN ROAD CONSTRUCTION.

 

High pattens.

So far as we are aware, there is no account of the condition of the roads in Tring before the era of modern road building, but an account of conditions in nearby Aylesbury does exist.  Writing in 1842, Mr. John Gibbs of Aylesbury had this to say:
 

“I recollect the year 1800.  At that date the general state of Aylesbury was wretched as compared with its present condition.  The footways with few exceptions were bad, neglected, and impassable; allowed to go to decay, they were repaired in a very rough and ready manner.  Kingsbury in wet weather was a morass, not ankle deep, but knee deep, in mud.  Walton Street was no bettor.  The outskirts of the town abounded in filthy ditches.  A wide gaping ditch was open all down the west side of Walton Street, and on the east side so had was the construction of the footway that a rail was requisite to keep foot passengers from tumbling into the road . . . . No one thought of entering the town by way of the Oxford Road, in fact from its miserable state it was impassable; the traffic then passed up Castle Street.  White Hill was in a like state; the street leading from the Nag’s Head Inn to the Buckingham Road was not considered public; it was with the greatest difficulty that foot passengers could make a way through it, from its bad state.  Dropshort was a slough; I have frequently trespassed on the adjoining meadow by crossing it, to avoid being stuck in the mud there.  In my young days, before the principal streets in the town were pitched [i.e. sealed with coal tar] by the Trustees of the Turnpike Roads, they were often ankle deep in mud; females without the aid of a pair of high pattens [see illustration] would not venture across them.”

Buckinghamshire: A History of Aylesbury with Its Borough and Hundreds, Robert Gibbs (1885).


The seeds of modern road construction in England were first sewn in Scotland, in difficult times.

 
General Wade (1673-1748) and the military roads of Scotland.

 

“Had you seen these roads before they were made,
 You would lift up your hands and bless General Wade.”

 

George Wade, soldier and military engineer.
His road builders are just discernable in the background.

So says doggerel engraved on an obelisk near Inverness.

The first new road network in any way comparable to that of the Romans was built for exactly the same purpose, to suppress a hostile population, a requirement that arose from the Jacobite uprisings. [4]  The road builder in question, General (later Field Marshall) George Wade (1673-1748), is not only remembered for his road-building achievement, but for appearing in the sixth verse of our National Anthem:
 

Lord, grant that Marshal Wade,
May by thy mighty aid,
Victory bring.
May he sedition hush,
And like a torrent rush,
Rebellious Scots to crush,
God save The King.


Wade was sent to Scotland in 1724 to “inspect the present situation of the Highlanders” and to “make strict inquiry into the last law for disarming the Highlanders”.  He reported that most Highlanders able to bear arms against the Crown were ready to do so — as later proved the case — and he recommended the construction of barracks, bridges and roads to help control the Highlands.  Having received and approved Wade’s report, King George I. then gave to Wade the task of implementing his recommendations ― and Wade built his military roads to last:
 

“The construction of these roads was not dissimilar to Thomas Telford’s practice eighty years later, in that a foundation of larger stones were laid to a depth of 18 inches, covered by a layer of gravel ideally as much as 3 feet deep, but sometimes only half that.  Facines [5] were used in lieu of the base course where roads crossed boggy ground, anticipating John Metcalf’s famous use of them after he returned home from the ‘Fortytfive’.  Banks, side-drains and cross drains served to remove the copious rainfall from the road.  The standard width was 16 feet, but 10 feet was not unknown.  About 40 bridges were built to 1736, a few each year, under contract by masons, some of whom came from the Lowlands for the work”

Biographical Dictionary of Civil Engineers, Prof. Sir Alec Skempton (2002).


A well-preserved section of General Wade’s Military Road near Melgarve,
leading to the Corrieyairack Pass. Only the foundation stones remain.

 

Wade’s bridge at Aberfeldy.

Construction took place between April/May and October of each year, the winter months being too harsh for work.  Work in the summer could be arduous too with uncertain weather and the presence of the ubiquitous midge.  The construction parties consisted of 100 men overseen by 2 corporals, 2 sergeants, 2 subalterns and a captain.  A soldier was expected to complete 1½ yards of road per day on reasonable ground, and was paid an additional allowance while so employed.

When Wade retired in 1745, work continued under Major (later Lieut-Colonel) William Caulfeild until his death in 1767, when the highland road-building programme ended.  By then, some 1,100 miles of road had been constructed, Wade being responsible for 300 and Caulfeild the remainder.  Many sections of these roads remain in use today in a modified form.  But perhaps the best known monument to Wade’s work is the bridge designed by William Adam over the Tay at Aberfeldy.


John Metcalf (1717-1810).

 

Blind Jack of Knaresborough.
Drawn by J R Smith in the Life of John Metcalf, published 1801.

In 1745, Wade was given command of an English army, his task being to confront the Jacobite army of Charles Edward Stuart (a.k.a. Bonny Prince Charlie) then invading England.  Among his contingent was John Metcalf [6], a musician and performer on the oboe and violin, who had a remarkably varied and successful career despite being blind from the age of six.  Although not a member of Wade’s road-building team, ‘Blind Jack’ was present at the English defeat by the Scots at Falkirk Muir (1746) — where, as a military musician, he played his company onto the field — and at the Duke of Cumberland’s defeat of the Jacobites at Culloden three months later.

Following his term in the Army, Metcalf had a spell at horse trading and then running a stage wagon business between York and Knaresborough.  While engaged in this latter occupation he took up a contract to build a 3-mile section of turnpike road between Harrogate and Boroughbridge, including a small bridge at the latter.  So commenced Metcalf’s career as a road-builder, during which he built some 180 miles of roads in Yorkshire, Lancashire, Derbyshire, and Cheshire.

Metcalf returned to Roman road-building principles.  He built on a firm foundation created by excavating any soft surface material until a firm footing was reached on which the bottom layer of stones could be placed.  He found that angular broken stones made a better foundation than smooth round ones, which were pushed aside when placed under load.  In order to deal with marshy areas Metcalf used fascines (as Wade had done before him) for the foundation, and built his road on top; this ‘floating roadway’ proved very successful, in many places enabling a more direct route to be taken (years later, George Stephenson used the same method to carry the Liverpool and Manchester Railway over the bog known as ‘Chat Moss’).  Atop the foundation, Metcalf created an elevated road surface, which he built smooth and convex to allow rainwater to drain quickly into roadside ditches.

The extent to which the methods of Wade and Metcalf influenced later road builders is unclear.  The great civil engineer Thomas Telford knew of Wade’s military roads, which he condemned as poorly aligned, steep, rough and badly drained — overall, “as to be unfit for the purposes of civil life”.  But this is unfair criticism, for Telford’s road-building brief was very different from that given to Wade and Caulfeild.  The fact remains that the Highland military roads were suitably engineered for their purpose, while there is every reason to believe that if the pair had been required to deliver roads for civil use — e.g. by mail coaches — they would not have lacked the necessary skills to build them.  Nevertheless there can be no doubt that the road works of the next two civil engineers were to have widespread influence.

 
Thomas Telford (1757–1834).

 

“Every valley shall be exalted, and every mountain and hill shall be made low; and the crooked shall be made straight, and the rough places plain.”

Isaiah xl. 4

 

Thomas Telford FRS, FRSE, civil engineer.

Commencing in about 1804, Thomas Telford began to deliver this biblical vision.  A stonemason by trade, Telford became a prolific civil engineer.  During his long career he was responsible for building a number of significant roads, canals and bridges, but not railways, which came to prominence at the end of his life.  Among his major achievements is the London to Holyhead road, the A5, which crosses the Menai Straits on the 579 ft span stone and wrought-iron Menai Suspension Bridge (begun in 1819 and completed seven years later).  But arguably his best known work is the 18-span, 126ft high iron trunk Pontcysyllte Aqueduct, which carries the Llangollen Canal over the valley of the River Dee at a point between Llangollen and Ruabon.

In 1815, Telford was appointed Engineer to the Holyhead Road Commissioners with responsibility for estimating the cost of a new road to link Holyhead with the Capital.  His estimates and designs having been accepted, an Act of Parliament was passed authorising the work (today one marvels at its trivial cost!):


“An Act to amend an Act passed in the Fifty fifth Year of His present Majesty, for granting to His Majesty the Sum of Twenty thousand Pounds towards repairing Roads between London and Holyhead by Chester, and between London and Bangor by Shrewsbury; and for giving additional Powers to the Commissioners therein named, to build a Bridge over the Menai Straits, and to make a new Road from Bangor Ferry to Holyhead, in the County of Anglesea”.

Public Act 1819, 59 George III., c. 48.


Telford’s method for road building required digging a trench, installing a foundation of heavy rock, and then surfacing with layers of smaller stones topped with gravel.  During construction, the centre of the road was raised, producing a crown that allowed water to drain off:
 

“In terms of construction his major roads were commodious, well drained and incorporated a hand-pitched stone foundation.  Unlike McAdam’s roads, they were properly engineered to improved lines and gentle gradients, and although more expensive initially, facilitated traction and reduced maintenance costs.  On its completion the Holyhead Road was described as ‘a model of the most perfect road making that has ever been attempted in any country’ (Sir Henry Parnell)”.

Biographical Dictionary of Civil Engineers, Prof. Sir Alec Skempton (2002).


 
John Loudon McAdam (1756-1836).

 

John Loudon McAdam, road builder.

By 1823, McAdam was advising 32 turnpike trusts and his three sons were responsible for 85 more, including the Sparrows Herne.  His road system became widely used both at home and abroad.

Although Telford’s method was faster and less expensive than that employed by the Romans, it was much more expensive than that of McAdam.

In 1783, McAdam became a trustee of the Ayrshire Turnpike and from then on he became increasingly involved with road construction.  In the 15 years from 1798, he claimed to have travelled 30,000 miles gathering information about road making and, of equal importance, road administration.  He was encouraged to present his ideas in evidence to Parliamentary enquiries, before which he argued that roads needed to be raised above the surrounding ground and constructed from layered rocks and gravel in a systematic manner.

Although both engineers were adamant on one point, the provision of adequate drainage, McAdam’s view — contrary to that of Telford — was that a well-drained roadbed did not require a foundation of large stones, carefully laid and infilled.  Instead, McAdam specified two layers of broken stones laid directly onto the subsoil.  First came a closely compacted 10 to 12-inch layer of stone that had been broken to an inch in diameter and which was raised in the centre by three inches to facilitate drainage.  This was followed by a carpet of finer-grained stone that was hand-rammed into place, the better the ramming the harder and smoother the running surface, which was further improved by filling the small surface gaps with sand and stone sweepings from the stone-breaking operation.[7]

Both engineers also provided a camber to get the surface water off the road, and outlets and ditches to ensure that the soil beneath the road did not become waterlogged.  However, not all stone is suitable for forming a good McAdam surface, a point taken up by an American journal on road engineering:
 

“An important item in the making of a Macadam road is the obtaining of broken stone of suitable quality and size.  It should have careful consideration, since it relates to the wearing surface of the roadway, and upon the quality of the stone used will largely depend the life of the Macadam crust and its smoothness.  A hard stone should be used; not hard in the sense that it is brittle, for many brittle stones are quite unfit for use as road metal, but rather stone of a tough texture such as will resist the abrasion of wheel tires and the crushing force of heavy loads.”



The writer then goes on to discuss the properties of several types of stone, among which is limestone:
 

“Limestones are both good and bad.  The softer limestones wear rapidly, form a road on which mud quickly collects, and roads of softer limestone yield readily to the action of the weather.  The upland or mountain limestones, on the other hand, are frequently well adapted for use as road metal.  They bind quickly and make a smooth and durable roadway.  The rubbing and wearing of limestones form a dust which, when wet, becomes a sort of mortar, filling the little spaces between the pieces of stone and consolidating the entire roadway into a solid and sometimes into a durable crust. Some of the best limestones are found in the Devonian and the older Silurian rocks.”

Good Roads, Vol. 4 No. 1, July 1893.


It was later found that compacting the road material was quickened using a heavy cast-iron roller, instead of allowing for compaction by traffic, and to answer this need the steamroller was developed.


Before the steamroller.


Generally speaking ― particularly where large stones were available ― Telford’s method of construction was preferred for many years.  However, the method of road construction has now reverted to that proposed by McAdam, i.e. a series of layers of relatively small aggregates with appropriate modifications to meet to requirements of present day traffic.

The steamroller.


As road making in Britain improved, heavy rollers hauled by men or by horses were used to compact the surface. [8]  Steam was first used to propel road rollers in the 1860s, and the ‘steamroller’ went on to give most of our roads their first compacted foundations and good running surfaces.  Steamrollers, their caravan (in which the driver sometimes lived with his wife and family) and water cart were once a familiar train on our roads as they progressed from job to job.

An Aveling & Porter steamroller. This firm built more steam rollers than all the
other manufacturers combined. They also built steam traction engines.


Steamrollers usually weighed between 10 and 15 tons, 10 tons being the most desirable for general use, as machines of this weight compacted well while not being so liable to damage drains, water pipes, and other utilities buried beneath the road.  Operating a steamroller was a two-man job, one man being responsible for maintaining steam pressure while the other steered and operated the gearing.  In a day’s work, a 10-ton steamroller could be expected to consolidate 1,500 yards of road material 4-inches thick, the rolling being done slowly to avoid crushing the stone.

The steamroller was to remain in use until the 1960s, one of its last major tasks being the construction of sections of the M1.

 

Laying a tar and chippings pavement.

The surface was first coated with tar. While the tar was still hot, the surface was covered with stone chippings evenly spread. A steamroller then rolled the surface to embed the chippings in the hot tar and complete the job.

 

‘Tarring’
(With apologies to Road Metalling)


The first to need was a hot sunny day
    And the whole of the Council ‘gang’,
With the tar barrels ready and waiting,
    We were off with ‘a clankity clang’!
The noise was the sound of ‘the boiler’,
    A large drum which was fixed to four wheels,
Tucked underneath was the fireplace
    To hot up the treacly black meals.

The road had been swept and well mended
    And all potholes were levelled as best,
The sweat and the toil just to follow
    And most of ‘the gang’ down to vest.
The foreman had name such as ‘Bullet’
    And his second in command was ‘Splash’,
When they gave the orders to action
    Then everything started to dash.

A tarry extension stuck out of the bin
    Where the hot thinning tar spurted out,
With a handle to turn it to on or off
    It was wielded and splashed all about.
Close on behind some of the gang
    With long handles and flaps like a rake,
All pushing and pulling ‘sploshing’ it out
    ‘The tar-bin-man’ put on the brake.


Standing at ready still further behind
    Were hoppers all running on wheels,
Two of gang to push-pull by hand
    Spreading shingle on tar to conceal.
You would think of time study in motion
    But these ‘blokes’ weren’t hanging about,
It was in and then out covered up quick
    Time to work ― not for mucking about.

Down with the tar and covered all up
    As ‘shovellers’ touched up the bare,
Then to sight of the action ‘a roller’
    A steam one the duty to share.
Backwards and forwards, water on wheels
    As it crunched and ‘metalled’ the lot,
Smooth as a baby’s ‘bot’ ’twas said
    As it rolled out all over the plot.

It was kind of a Stephenson’s ‘Rocket’
    On the road and a sight to behold,
When the word came to ear “they’re tarring”
    Such excitement for all could unfold.
Not least of course for the children
    An excuse for the elder to see,
It’s another repeat and repeating
    Just one more thing “you aren’t gonna see”!

Ron Kitchener,
from JUST “RAMBLING ON WITH ME.


――――♦――――

 
MODERN ROAD BUILDING.


The problem with unsealed roads.


An early motorist (1904) with accompanying dust cloud.


Telford’s and Macadam’s roads were a great improvement on their predecessors; nevertheless they suffered the disadvantage of having unsealed surfaces, which gave rise to dust in dry weather (and the need in towns for suppression by water-spraying) and mud when wet.  With the arrival of faster-moving motor traffic, the dust and mud it raised became even more of a problem.  McAdam’s roads were also subject to erosion by heavy rain and they proved to have insufficient strength to accommodate motor traffic; in this respect Telford’s system of a heavy foundation had the advantage, particularly when mechanised road building equipment became available making it much easier to obtain, place and compact large thicknesses of crushed rock.  Added to these problems, the loose chippings from unsealed road surfaces thrown up by faster moving motor vehicles were a danger to other road users and pedestrians, while exposed sharp edges from the road’s sub-layer risked puncturing their pneumatic tyres.

Before moving on to outline today’s approach to road construction, it is necessary to distinguish between three road building materials that were to come into widespread use in countering the above-mentioned problems, the names of which are often used interchangeably although the materials are quite different.
 

Tar (also called pitch): a sticky, black, highly viscous thermoplastic [9] liquid obtained by the destructive distillation of a variety of organic materials including wood and coal.  Originally used to seal the gaps in the planking of wooden ships (‘caulking’), tar was later used to bind the aggregates used in road construction due to its good adhesive and waterproofing properties.  Tar used for this purpose was produced as a by-product from heating coal to extremely high temperatures in the manufacture of town gas and coke.

Bitumen: a sticky, black and highly viscous thermoplastic liquid or semi-solid form of petroleum.  It is found in natural deposits [10] or obtained as a refined product of crude oil.  Bitumen has now replaced tar as a binding agent, tar being more sensitive to temperature change than bitumen, less readily available (since the demise of town gas), and subject to health concerns in its use.

Asphalt: a mixture of aggregates, binder and filler, which forms a strong, waterproof surface when it sets.  The aggregates used for asphalt include crushed rock, sand, gravel or slag.  A binder, generally bitumen, is used to bind the aggregates into a cohesive mass.  In its manufacture, bitumen is heated to around 150°C and mixed with a flux (kerosene); water and other chemicals may also be added.  The aggregates are then added and mixed in.


Methods to stabilise unsealed surfaces with tar date back to at least 1834 when John Henry Cassell patented ‘pitch macadam’.  This method involved spreading tar on the ground (the ‘subgrade’), building a macadam road on top, and finally sealing the surface with a mixture of tar and sand.  Another process, ‘tar-grouted macadam’, involved scaring an existing macadam surface, spreading tar, and re-compacting.  However, little use was made of tar until the arrival of the motor vehicle at the start of the 20th century and the invention of Tarmac.

 
Tarmac —Edgar Purnell Hooley (1860–1942).


The story has it that, in 1901, Edgar Hooley, County Surveyor to Nottinghamshire County Council, was passing a tarworks when he noticed that a barrel of tar had been spilled on the road.  In an attempt to reduce the mess, gravel had been dumped on top of it, the result being that the area was remarkably free from dust compared to the surrounding road.  From this observation Hooley went on to develop and patent ‘Tarmac’ (short for ‘Tarmacadam’).  Hooley’s invention was to change the way we live by, quite literally, paving the way for the motorised world we now inhabit.

The production of Tarmac originally involved mechanically mixing tar — which had been modified by adding small amounts of Portland cement, resin, and pitch — and aggregate (slag) prior to road surfacing.  As petroleum production increased, bitumen became available as a by-product and supplanted tar.

Tarmac is a registered trade mark for a specific product, whereas ‘asphalt’ is a generic term for a similar group of road surfacing materials.  The basic premise of a Tarmac or asphalt surface is that the material is prepared, transported to site in insulated wagons, laid while hot and viscous, and levelled and compacted by rolling as quickly as possible.  It is then allowed to cool so that it sets, and each particle becomes firmly bound to its neighbours.  Two courses are usually laid.


Structural layers in a modern road.


Wearing course: designed to withstand the direct tractive forces from traffic and the effects of weather, and also to provide an even-running, skid-resistant and durable finish.

Basecourse: its purpose is to provide a good shaped surface on which to lay the wearing course and also to distribute the traffic loads over the roadbase.


The wearing course and basecourse are collectively called the
surfacing and are the two layers commonly used in the regulating, strengthening and maintenance of flexible roads when levels permit the superimposition of additional material.

Roadbase: is the main load-bearing or distributing layer in the road structure and will be 4 inches (102mm) or more thick, depending on the intensity of the traffic for which the road is designed.

Sub-base: the layer of relatively weak material between the roadbase and the formation. Its thickness depends on the intensity of traffic and also the nature of the subgrade.  The main objects of the sub-base are to:

  •     give a further and final distribution of loads on to the subgrade;

  •     provide an adequate thickness of frost-resistant material;

  •     provide a working platform on which to lay the main layers of construction.

From Modern Flexible Road Construction


Building a new road.


As previously mentioned, our earliest roads were tracks beaten out by travellers making their way as best they could from place to place, taking lengthy detours en route to cross rivers at fords, choosing high ground to avoid the bogs of the valleys, and deviating from a straight course wherever they encountered an obstacle — it might even be said that these early roads made and maintained themselves.  Road construction today could not be more different, for this branch of civil engineering involves — sometimes on a large scale — planning, design and construction, each of which is a major discipline that can involve many skilled people.

The first step is planning.  The aim is to decide what type of road is required; this will depend on the type and volume of traffic it is to carry.  Estimating traffic volumes and their impact involves looking further afield, for a new road is likely to suck in traffic from elsewhere.  For instance, drivers might find it worthwhile to make a detour to a new road in order to use it in preference to one that is older and more congested; this will increase traffic congestion on connecting roads.  People might find a new road makes travel to new destinations much more convenient and attractive, which will increase traffic flows, both to and at those locations.  A new road might require many different structural elements in the form of cuttings, embankments, tunnels and bridges; these also need to be planned.  Thus, while a simple road might take months to plan, it can be years before the construction of a major road can begin.

Other factors that road planners must consider include cost, the availability of materials, and road safety, while the potentially damaging environmental impacts of a new road must be analysed and managed where necessary.  These include impact on habitat and bio-diversity; the creation of air, water, noise/vibration pollution; damage to the natural landscape; the need to demolish existing buildings (that might be of historic interest); and damage to a community’s social and cultural structure (e.g. from large-scale housing demolition).

Toward the end of the planning phase, surveyors and construction experts produce their plans for the new road.  At this stage public enquiries are sometimes held so that people directly affected by the scheme can voice their opinions/protests; some, including pressure groups, might object to the choice of route and its impact on communities, existing buildings and the landscape/natural environment.  Such enquiries can run over years before a final decision on the route of a new road is given. [11]  When approval is obtained, that part of the road that lies over privately owned land will be subject to land purchase negotiations involving compulsory purchase. [12]

The Highways Agency is the government body tasked with building new roads. It solicits bids from road building contractors, the aim being to ensure that the taxpayer receives optimum value for money from the construction project.

Once bids are compared and a contractor selected, work on the new road can begin.  Depending upon the type of road project, this can take from several months to several years.  The first stage is one of the most important — earthwork.  Huge earth-moving machines are used to create a solid foundation for the road, without which the road will fail long before its expected lifespan.  Bulldozers and graders move around dirt delivered by dump trucks to create a compacted, level surface that will support the road for years to come.  Aggregates are then added in layers and machines roll the surface to compact and flatten it further.  Drains and storm sewers [13] are also installed at this early stage, so that rain will drain away from the road surface and make it easier for vehicles to travel in stormy weather.


Earth moving equipment: bulldozer, grader and dump truck.


When the foundation is complete and has been inspected, the pavement can be laid.  The most common material used for paving roads is asphalt.  This is heated to about 150°C and transported to site in insulated trucks, where it is spread and compacted onto the road foundation in several courses.  The final tasks include painting road marking and installing crash barriers, road signs, lighting, emergency telephones and landscaping.

Road maintenance.

Most road surfaces are made of asphalt, still colloquially called tarmac although tar is no longer used as a binder.  When new, asphalt is able to flex and stretch a little, but as it gets older the bitumen binder becomes brittle, and cracks can then open in the road surface.  Water then penetrates, freezes and in so doing widen the cracks.  This ‘freeze-thaw’ effect can lead to a rapid deterioration of the road surface and the formation of potholes, which is why they are more common in cold, wet weather.  If this deterioration continues, water can seep into the lower layers of the road, damaging them too.  For this reason, keeping the surface sealed is key to getting the most life out of a road.

Road rebuilding is very expensive, so the practice is to concentrate resources (always in short supply) on keeping the existing road surface watertight.  For this reason surface treatment is considered before more drastic measures, such resurfacing or reconstruction:


Surface treatment: involves extending the life of the road by laying a thin layer of asphalt over the existing surface to seal it and restore grip.  Cracks and potholes are also filled as part of the process or through pre-patching work done in advance of the surface treatment;

Resurfacing: usually involves removing and replacing the existing road surface, although it is sometimes possible to lay the new surface on top of the old.  Resurfacing differs from surface treatment in that a thicker layer of material is applied, from 30mm to 100mm or more if several layers of the road are replaced.  Resurfacing restores the road surface to a new condition, removing surface problems and most unevenness.


The process of road building has changed dramatically over the past century, moving from large gangs of workers with picks and shovels to enormous specialised machinery.  Today, an old road surface is removed by a process called ‘planing’ where a large machine with a toothed rotating drum chews off the old surface.  While noisy and dusty, the process is quick.  Sometimes only the surface layer is removed (30-40mm) but if the damage to the surface is deeper then more of the existing road will be removed in this way.  The ground up surface is dumped directly into trucks for recycling.  The planed surface is then cleaned and sprayed with bitumen to help the new asphalt stick to it.


Planing.


New asphalt is brought to site from the asphalt manufacturing plant in insulated lorries and laid at a high temperature by a paving machine, which lays a controlled thickness that is then rolled to compact it and form an even surface.


A paving machine. Hot asphalt is being loaded into its hopper by
the insulated truck at the rear.


The sheer weight of traffic on busy main roads eventually causes damage that requires deep structural work to correct.  This involves digging down to repair or replace some or all of the foundation layers of the road, and then laying a new surface on top.  The process varies considerably depending on the structure of the road and the nature of the problems, but it usually involves removing the old road and replacing or repairing the structural foundation layers.  This typically means removing the surface layers as if resurfacing the road, and then digging out the layers below using excavators.  These layers can then be replaced with new ones and new surface layers laid on top.


Who maintains our roads?


In England, the maintenance of motorways and trunk roads are the responsibility of the Highways Agency, an executive agency of the Department of Transport responsible for operating and maintaining our strategic road network.  Other public highways are the responsibility of county and city councils.


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FOOTNOTES.

 
1. From the beginning of human history, people have dragged loads too heavy to be carried.  But large objects are often of awkward shape and texture, liable to snag on any roughness in the ground.  The natural solution is to move them on a platform with smooth runners, a sledge.  Sledges are not only useful in winter, but can be drawn over wet fields, muddy roads, and even hard ground.
 
2. If a firm foundation could not be readily attained due the swampy nature of the ground or from any peculiarity in the soil, a corduroy road foundation was formed artificially using logs; conversely, if the route led over a rocky surface, excavation might be dispensed as the terrain formed a sufficiently load-bearing foundation.
 
3.

“In Britain we find considerable variation in the Roman method of construction.  An embankment is a very usual feature, and, constructed with the utmost care on a solid foundation with suitable materials, it constitutes the ridge of the road, which often remains almost unchanged by time when man has not disturbed it.  The height of the embankment or ridge was sometimes considerable, not only where a low place had to be crossed, but on high ground.  Perhaps the most striking example remaining is the embankment called Atchling Ditch or Dyke to the south-west of Salisbury, which for four miles runs across the high open down almost unchanged in profile, five yards across the top and five to six feet high.  Another example may be seen between Doncaster and Pontefract, where for several miles there is an embankment four, six, and eight feet high, and six yards wide, on high ground with a rock subsoil.”

Roman Roads in Britain, Thomas Codrington (3rd edition, 1918).

 
4. The Jacobite risings were a series of uprisings, rebellions and wars in Great Britain and Ireland that occurred between 1688 and 1746.  Their aim was to restore the Stuart kings, the last of whom, James II (Jacobite is derived from Jacobus, the Latin form of James), had been deposed and exiled in 1688.  Although each Jacobite rising had unique features, they were part of a larger series of military campaigns by Jacobites, culminating in the Battle of Culloden in 1746.
 
5. Fascine: a cylindrical bundle of small sticks of wood, bound together, used in raising batteries, filling ditches, strengthening ramparts, and making parapets; also in revetments for river banks, and in mats for dams, jetties, etc.
 
6. Metcalf was born at Knaresborough in 1717 and died at Spofforth near Knaresborough in 1810, aged 92.  His fascinating life is recorded in a biography, The life of John Metcalf, commonly called Blind Jack of Knaresborough (1795).
 
7. Remarks on the Present System of Road-Making and Practical Essay on the Scientific Repair and Preservation of Roads, by John Loudon McAdam, published in nine editions between 1816 and 1827.
 
8. It is sometimes believed that rolling levels the ground; it does not. Rolling compacts (or consolidates) the road materials.  If these have been laid on an unlevelled surface, it will remain so after rolling.
 
9. A material that softens when heated and hardens again when cooled.
 
10. The World’s largest natural deposit of bitumen is claimed to be the Pitch Lake (a.k.a. Lake Asphalt) in Trinidad, which covers about 40 hectares and is believed to be 75m deep.
 
11. Some examples are the Newberry bypass and the Stonehenge road tunnel schemes.  The Stonehenge scheme was first proposed in 1995.  After protests and public enquiries in 2004 and 2011, work finally commenced on an alternative scheme in 2012.  Between January 1996 and April 1996 the clearance of approximately 360 acres of land including 120 acres of woodland, and the felling of nearly 10,000 mature trees to make way for the construction of the Newberry bypass, led to some of the largest anti-road protests in European history.  Around 7,000 people demonstrated on the site of the bypass route in some way and over 800 arrests being made.  By December 1996, the cost of policing the protest had reached approximately £5 million.  An additional £30 million was spent on private security guards, security fencing, and security lighting while the works were in progress, of which only £7 million was budgeted for in the original contract.  The road was eventually finished in November 1998 at a cost £104 million, against the original contract price of £74 million.
 
12. Compulsory purchase is the power to acquire rights over an estate in English land law, or to buy that estate outright, without the current owner’s consent — but in return for compensation.  In England and Wales Parliament has granted several different kinds of compulsory purchase power, which are exercisable by various bodies in various situations.  Such powers are for the public benefit, but this expression is interpreted very broadly.  Compulsory purchase orders can be issued by local authorities, highways authorities, Regional Development Agencies, English Partnerships, and, in the case of Greater London, English Heritage. In all cases, public bodies are expected to exhaust other options before issuing a compulsory purchase order.
 
13. Storm sewer (or storm drain): a system designed to carry rainfall runoff and other drainage, but not sewage or hazardous wastes.  The runoff is carried in underground pipes or open ditches and discharges untreated into local streams, rivers and other bodies of surface water.


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