1. Highway Engineering-I

2. History of Highway Engineering
Road transport is one of the most common modes of transport.
Roads in the form of track ways, human pathways etc. were used even from the pre-historic times. Since then many experiments were going on to make the riding safe and comfort. Thus road construction became an inseparable part of many civilizations and empires.
The history of highway engineering gives us an idea about the roads of ancient times.
Roads in Rome were constructed in a large scale and it radiated in many directions helping them in military operations. Thus they are considered to be pioneers in road construction.

5. Ancient Roads
The first mode of transport was by foot.
The next major mode of transport was the use of animals for transporting both men and materials.
Since these loaded animals required more horizontal and vertical clearances than the walking man, track ways emerged.
The invention of wheel in Mesopotamian civilization led to the development of animal drawn vehicles.
Then it became necessary that the road surface should be capable of carrying greater loads. Thus roads with harder surfaces emerged.
Traces of such hard roads were obtained from various ancient civilization dated as old as 3500 BC.
The earliest authentic record of road was found from Assyrian empire constructed about 1900 BC.

7. Roman roads
The earliest large scale road construction is attributed to Romans who constructed an extensive system of roads radiating in many directions from Rome.
Romans recognized that the fundamentals of good road construction were to provide good drainage, good material and good workmanship. Their roads were very durable, and some still exist.
Roman roads were always constructed on a firm - formed sub grade strengthened where necessary with wooden piles.
The roads were bordered on both sides by longitudinal drains.
In the case of heavy traffic, a surface course of large 250 mm thick hexagonal flag stones were provided. A typical cross section of roman road is given in Figure.1

8. Figure.1 Roman roads

9. British roads
The British government also gave importance to road construction.
The British engineer John Macadam introduced what can be considered as the first scientific road construction method.
Stone size was an important element of Macadam recipe.
By empirical observation of many roads, he came to realize that 250 mm layers of well compacted broken angular stone would provide the same strength and stiffness and a better running surface than an expensive pavement founded on large stone blocks. Thus he introduced an economical method of road construction.
The mechanical interlock between the individual stone pieces provided strength and stiffness to the course.

12. Modern roads
The modern roads by and large follow Macadam's construction method. Use of bituminous concrete and cement concrete are the most important developments. Various advanced and cost-effective construction technologies are used.
Development of new equipments helps in the faster construction of roads.
Many easily and locally available materials are tested in the laboratories and then implemented on roads for making economical and durable pavements.

13. Highway Functional Classification
Highways are classified according to their functions in terms of the service they provide. Highways and streets are categorized as rural or urban roads, depending on the area in
which they are located.
This initial classification is necessary because urban and rural areas have significantly different characteristics with respect to the type of land use and population density, which in turn influences travel patterns. Within the classification of urban and rural, highways are categorized into the following groups:

16. Urban Principal Arterial System:
This system of highways serves the major activity centers of the urban area and consists mainly of the highest-traffic-volume corridors.
It carries a high proportion of the total vehicle-miles of travel within the urban area including most trips with an origin or destination within the urban area. The system also serves trips that bypass the central business districts (CBDs) of urbanized areas.

17. (3) Other principal arterials (with partial or no controlled access).
Highways within this system are further divided into three subclasses based mainly on the type of access to the facility:
Interstate, with fully-controlled access and grade-separated interchanges;
Expressways, which have controlled access but may also include at-grade intersections; and
(3) Other principal arterials (with partial or no controlled access).

18. A rural stretch of Interstate 5 in California, with two lanes in each direction separated by a large grassy median, and with cross-traffic limited to overpasses and underpasses

19. Expressways, which have controlled access but may also include at-grade intersections

20. Urban Minor Arterial System
Streets and highways that interconnect with and augment the urban primary arterials are classified as urban minor arterials.
The spacing of minor arterial streets in fully developed areas is usually not less than 1 mile, but the spacing can be 2 to 3 miles in suburban fringes.

22. Road and Highway Types The roads can be classified in many ways.
The classification based on speed and accessibility is the most generic one.
The accessibility of road increases, the speed reduces.
Accordingly, the roads can be classified as follows in the order of increased accessibility and reduced speeds.

23. Freeways Expressways Freeways are access-controlled divided highways.
Most freeways are four lanes, two lanes each direction, but many freeways widen to incorporate more lanes as they enter urban areas.
Access is controlled through the use of interchanges, and the type of interchange depends upon the kind of intersecting road way (rural roads, another freeway etc.)
Expressways
They are superior type of highways and are designed for high speeds (120 km/hr is common), high traffic volume and safety.
They are generally provided with grade separations at intersections.
Parking, loading and unloading of goods and pedestrian traffic is not allowed on expressways.

24. Freeway
In the field of road transport, an interchange is a road junction that typically uses grade separation, and one or more ramps, to permit traffic on at least one highway to pass through the junction without directly crossing any other traffic stream.
A Ramp is a segment (or set of segments) that connects two roads that don't physically intersect.

25. What is the difference between FREEWAY and EXPRESSWAY
Freeway is the equivalent of what used to be called "Controlled Access Roads". These are roads that can only be accessed by ramps (no traffic lights), and are free from slow-moving traffic.
Expressway is the equivalent of what used to be called "Limited Access Roads". These roads may have some interchanges or stop signs where local roads connect to it.

26. Highways
They represent the superior type of roads in the country.
Highways are of two types – rural highways and urban highways.
Rural highways are those passing through rural areas (villages) and
urban highways are those passing through large cities and towns, ie. urban areas.
Arterials
It is a general term denoting a street primarily meant for through traffic usually on a continuous route.
They are generally divided highways with fully or partially controlled access. Parking, loading and unloading activities are usually restricted and regulated.
Pedestrians are allowed to cross only at intersections/designated pedestrian crossings.

27. Local streets Collector streets
A local street is the one which is primarily intended for access to residence, business or abutting property.
It does not normally carry large volume of traffic and also it allows unrestricted parking and pedestrian movements.
Collector streets
These are streets intended for collecting and distributing traffic to and from local streets and also for providing access to arterial streets.
Normally full access is provided on these streets. There are few parking restrictions except during peak hours.

29. Road Classification Criteria
Based on usage
This classification is based on whether the roads can be used during different seasons of the year.
All-weather roads
Those roads which are negotiable during all weathers, except at major river crossings where interruption of traffic is permissible up to a certain extent are called all weather roads.
Fair-weather roads
Roads which are negotiable only during fair weather are called fair weather roads.

30. Based on carriage way
This classification is based on the type of the carriage way or the road pavement.
Paved roads with hard surface: If they are provided with a hard pavement course such roads are called paved roads. (eg: stones, Water bound macadam (WBM), Bituminous macadam (BM), concrete roads)
Unpaved roads: Roads which are not provided with a hard course of at least a WBM layer they are called unpaved roads. Thus earth and gravel roads come under this category.

31. Other criteria
Roads may also be classified based on the traffic volume in that road, load transported through that road, or location and function of that road.
Traffic volume: Based on the traffic volume, they are classified as heavy, medium and light traffic roads. These terms are relative and so the limits under each class may be expressed as vehicles per day.
Load transported: Based on the load carried by these roads, they can be classified as class I, class II, etc. or class A, class B etc. and the limits may be expressed as tonnes per day.
Location and function: The classification based on location and function should be a more acceptable classification since they may be defined clearly. ( Ex: National highways, state highways, major district roads and other district roads)

32. Road Classification Criteria
Based on usage
This classification is based on whether the roads can be used during different seasons of the year.
All-weather roads
Those roads which are negotiable during all weathers, except at major river crossings where interruption of traffic is permissible up to a certain extent are called all weather roads.
Fair-weather roads
Roads which are negotiable only during fair weather are called fair weather roads.

33. Based on carriage way
This classification is based on the type of the carriage way or the road pavement.
Paved roads with hard surface: If they are provided with a hard pavement course such roads are called paved roads. (eg: stones, Water bound macadam (WBM), Bituminous macadam (BM), concrete roads)
Unpaved roads: Roads which are not provided with a hard course of at least a WBM layer they are called unpaved roads. Thus earth and gravel roads come under this category.

34. Based on pavement surface
Based on the type of pavement surfacing provided, they are classified as surfaced and unsurfaced roads.
Surfaced roads (BM, concrete): Roads which are provided with a bituminous or cement concreting surface are called surfaced roads.
Unsurfaced roads (soil/gravel): Roads which are not provided with a bituminous or cement concreting surface are called unsurfaced roads.

35. Highway Administration in Oman
In Sultanate of Oman roads and highways comes under Ministry of Transport and Communications, Muscat ( ).

46. Traffic Characteristics

47. Introduction Inventories
Traffic studies may be grouped into three main categories:
Inventories
Inventories provide a list or graphic display of existing information, such as street widths, parking spaces, transit routes, traffic regulations, and so forth. Some inventories—for example, available parking spaces and traffic regulations—change frequently and therefore require periodic updating; others, such as street widths, do not.

48. 2) Administrative studies
Administrative studies use existing engineering records, available in government agencies and departments. This information is used to prepare an inventory of the relevant data. Administrative studies include the results of surveys, which may involve field measurements and/or aerial photography.
(3) Dynamic studies
Dynamic traffic studies involve the collection of data under operational conditions and include studies of speed, traffic volume, travel time and delay, parking, and crashes.

49. Spot speed studies are conducted to estimate the distribution of speeds of vehicles in a stream of traffic at a particular location on a highway.
The speed of a vehicle is defined as the rate of movement of the vehicle; it is usually expressed in miles per hour (mi/h) or kilometers per hour (km/h).
A spot speed study is carried out by recording the speeds of a sample of vehicles at a specified location.
Speed characteristics determined from a spot speed study may be used to:
Establish parameters for traffic operation and control, such as speed zones, speed limits and passing restrictions.

54. The "mean" is the "average" you're used to, where you add up all the numbers and then divide by the number of numbers.
The "median" is the "middle" value in the list of numbers. To find the median, your numbers have to be listed in numerical order, so you may have to rewrite your list first.
The "mode" is the value that occurs most often. If no number is repeated, then there is no mode for the list.

62. Traffic volume studies are conducted to collect data on the number of vehicles and/or pedestrians that pass a point on a highway facility during a specified time period.
Time period varies from as little as 15 minutes to as much as a year depending on the anticipated use of the data.
Traffic volume studies are usually conducted when certain volume characteristics are needed, some of which follow: