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ECross-section of a road

FNecessary and important things

GThe form of a road

19.Look through the text again and give the definitions of the underlined words. Use your dictionary if necessary.

20.Unscramble the words from the text:

21. Work in groups. Draw up the mind maps.

Verbs:

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22.Try to describe highways using the words from your mind map.

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23. In the text (Highway design) find the synonyms to the words in the box.

Do you know any other synonyms to the given words?

24.Work in pairs. Ask each other questions about highway design and answer them.

25.Write a short article for a students’ book about highway design (about 120 – 180 words). Do not forget to draw pictures.

26.Study the following words:

alignment – выравнивание; трасса, разбивка cross section – поперечное сечение, разрез cut – выемка

design – 1) проектирование; разработка; конструирование || проектировать; разрабатывать; конструировать; 2) проект; разработка; конструкция, конструктивное решение; 3) схема; чертёж; план

fill – насыпь

grade – уклон, подъем

maintenance – содержание и техническое обслуживание, эксплуатация slope – склон, откос

soil – почва, грунт

surface – поверхность, покрытие tangent – касательная

urban – городской

27. Translate the sentences containing the words to be remembered into Russian:

1. Good appearance is also intimately integrated in almost every element of highway design. 2. Highways with long tangents, possibly inspired by the railroads, have proved more dangerous to traffic than a curving alignment. 3. The flattening of grades is generally desirable near intersections or wherever a driver will be encouraged to look away from the pave-

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ment.4. The design of the cross section of drainage ways has changed radically in keeping with other streamline cross sections in highway design. 5. The width of shoulders and drainage ways may become standardized, but the slope of cuts and fills should be specially designed to meet the controlling conditions of the site.

28. Arrange the words with the same meaning.

For example: urban, city.

Plan, urban, vehicle, city, slope, design, grade, automobile, hollow, maintenance, cut, fill, upkeep, embankment.

29. Transform the following sentences from Active into Passive Voice:

1.At the early time, the railroad engineering influenced the highway design.

2.Railroad engineers built long tangents and flattened grades.

3.The design of a highway includes, as a rule, two main principles – safety and efficiency.

4.The design of a highway provides also the economy of construction and maintenance of a road.

30. Guess the meaning of the following words, basing on their phonetic and graphic similarity with the Russian words:

Phases, automobile, masses, methods, period, principles, engineering, tangents, natural, maximum, efficiency, logically, economy, location.

31.Find in the text sentences in Present Indefinite, Past Indefinite and Present Perfect. Point out their functions in the text.

32.Have methods of designing highways changed a lot? Read the text and check your answer.

Development of highway design

The last fifty years in the history of highways have seen the effect of the automobile on many phases of highway design. It is probable that the increase of population, changes in the distribution of the masses of people in line with the trend of dispersed urban development, and the accompany-

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ing growth and changes on motor vehicles will cause far greater changes in the manner and methods of designing highways.

During that early period, highway design was influenced by certain principles of railroad engineering. Long tangents and flattened grades were built which meant deep cut and high fills. It also meant, as for the railroads, a rigidly uniform slope on both cuts and fills. The new slopes frequently lay close to the angle of repose of the soil and met the natural surfaces with angular precision.

It is significant to realize that the design of a highway must first and always provide for maximum safety – next, for efficiency. If each of these is properly included, it logically follows that economy of construction and maintenance are also provided.

Highway location, highway alignment, highway profiles and the cross section constitute a highway design.

33. Answer the questions.

1.What is the main trend of developing of highways?

2.What are the main demands for a highway?

3.What constitutes a highway design?

34. Read and study the following words:

centre line – ось полотна дороги circular curve – круговая кривая

curve (curvature) – кривая, изгиб (кривизна) grade line – продольный уклон

horizontal alignment – горизонтальная проекция horse-drawn transport – гужевой транспорт junction – соединение, стык

reverse curve – обратная кривая runoff – отгон виража

skidding – боковое скольжение, занос автомобиля superelevation – подъем виража

thrust – боковое давление, удар, толчок

vertical alignment – проектная линия на продольном профиле дороги

35. Find sentences with modal verbs and infinitives of purpose used to express requirements for the alignment in the texts about alignment.

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The curvature reduces the road quality because the stability of the motorcar and the safety of traffic on the curves become less. While moving on the curve the motor-car undergoes the centrifugal force which results in skidding and side thrust. The comfort of driving also decreases.

The safety of traffic is less not only because of the motor car stability decrease but because of the sight distance decrease as well if the curve is located in a cut, in a forest or in a built-up area particularly in the night time when the head-lights are directed nor along the curve but along a tangential.

To secure the stability of the motor-car against the side thrust on the curves with a small radius the road is superelevated.

Superelevation is a one side slope cross-section.

To ensure a good riding quality of the road the curves are made of a big radius, the transition curves are used, the pavement on curves is widened. The widening is designed depending on the curve radius and the designed traffic speed. The widening should be placed on the inside edge of the pavement, all the obstacles on the inside edge are elimimated.

The superelevation is designed along the whole circular curve. Since it is impossible to insert the superelevation suddenly it must be attained in a convenient distance termed the runoff. The length of the runoff is designed depending on the runoff slope. When the transition curves are used, the superelevation is zero at the beginning of the spiral and increases directly with the distance, as does the degree of curvature, and attains its full amount at the circular curve. In this way the superelevation and curvature are at all times in accord, which results in good appearance and good riding qualities.

Circular curves.

A simple curve is the arc of a circle connecting two tangents. The radius of a circular curve is determined according to the traffic speed, the crosssection, the quality of the pavement.

The circular curve must conform to the topography or to traffic needs. In days of horse-drawn traffic radii were generally quite short. The higher speeds of motor traffic demanded flatter radius curves with the result that the radius for the right-angled turns has been gradually increasing. Local conditions must necessitate shorter radii in which case the curves become points of potential, if not actual, congestion and danger. They should, therefore, be adequately marked and made as safe as possible.

A compound curve is a continuous curve in one direction composed of two or more simple curves placed end to end with a common tangent at the

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junction. A reverse curve adds to the steering difficulties especially if sharp. If the curves are superelevated, the superelevation must change side and this cannot be suddenly.

Vertical Alignment

The position of a highway in the vertical plane is given by its grade line. The grade line is analogous to the centre line in horizontal alignment and, like it, is made up of tangents connected by curves. The tangents are termed straight grades while the curves are known as vertical curves.

Direct grade lines of any considerable length are rarely obtainable, because they are very likely to require prohibitive cuts and fills. Consequently, the indirect grade line which dips into valleys and climbs over ridges is the normal one.

So the vertical curves should be used freely and always of ample length.

To ensure the smoothness of traffic the minimum length is rarely less than 20 m. The length should be chosen which fits the topography the best.

Where two straight grades connect, the grade line is rounded off with a vertical curve, which is exactly analogous to the horizontal curve. Since the intersection angle is always small and gravity constantly holds the vehicle to the roadway, the effect of centrifugal force is imperceptible and the application of vertical curves is less complicated than horizontal curves.

At summits of steep grades the length of the curve may depend on the necessary sight distance. The present tendency is towards the curves with greater radius.

The grade line with long easy vertical curves which fit the topography are much more pleasing in appearance as well as safer and more convenient, than the one with short choppy curves.

1.Why isn’t the ideal alignment always possible?

2.What purpose is central line used for?

3.What is the normal alignment?

4.Why is curvature dangerous?

5.Why is the road superelevation made for?

6.What is done to ensure good riding qualities of a road?

7.What does the length of the curve depend on?

8.What is a grade line made up of?

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40. Read the text and find the difference between alignment and profile.

Alignment and Profile

After a route has been selected, a three-dimensional road alignment and its associated cross-sectional profiles are produced. In order to reduce the amount of earth to be moved, the alignment is adjusted where practical so that the earth to be excavated is in balance with the embankments to be built. Computers allow many options to be explored and realistic views of the future road to be examined.

Design standards help to determine the actual alignment of the road by specifying, for each design speed, the minimum radius of horizontal curves, the maximum vertical gradient, the clearance under bridges, and the distance a driver must be able to see the pavement ahead in order to stop or turn aside.

41. Try to find the picture of road alignment and road profile (Pic. 15 - 16). Why do you think so?

Pic. 15

Pic. 16

42. You are going to read the text about highway structure. Do you know anything about it? Read the text and divide it into several paragraphs supplying each with a title.

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When vertical pressure is exerted locally on the pavement it sends, and hence produces additional pressure on the subgrade. The ability of the subgrade to resist deformation under this pressure depends on its stiffness, and this is measured by the “modulus of subgrade reaction”. The modulus of subgrade reaction, now universally known by the symbol “k”, is the number of pound per square inch of subgrade reaction per inch of slab deflection. It is expressed as pounds per square inch per inch (lb per sq. in per in.) or pounds per cubic inch (lb per cu in.). When a pavement slab is laid directly on the subgrade, the phenomenon knows as “mud pumping” is very apt to occur. It thus is important that a granular nonpumping subbase be used when the subgrade is of the type that will be damaged by mud pumping.

The base course rests directly on top of the roadbed and is often made up of compacted gravel. If the roadbed material itself is suitable, it may be treated, or stabilized, and used as the base. Soil can be stabilized by adding or mixing materials such as calcium chloride, bituminous material, lime, or portland cement to the soil. For very inexpensive, light-traffic roads, stabilized soil alone can suffice as the finished road surface. Drainpipes are usually installed within the base course to control rain and moisture drainage. Without adequate drainage, roads may buckle or collapse as water swells the ground underneath. Some roads include a second base layer, called the top course, for extra support.

Thus, the purposes of the subbase are to prevent mud pumping, reduce frost damage, control moisture in subgrade soils having high volume change, and improve the constancy and effectiveness of pavement support.

A road’s top layer, which directly supports moving vehicles, is called the wearing course. It is made of a solid layer of pavement and is designed to be smooth and to withstand erosion from traffic and weather. Two main types of pavements are used – bituminous, or flexible, pavement and concrete, or rigid, pavement. Bituminous pavement is cheaper and easier to construct, but it requires more maintenance. Concrete pavement lasts for a very long time with minimal upkeep but is much more expensive and timeconsuming to build.

43. Read the definition of the following words and try to find the Russian equivalent. It would be fine if you memorize these words.

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