PAVEMENT
ROAD
HIGHWAY

COMMON ACRONYMS
HWY, RD, ST

SOURCES OF INFORMATION/ COMMON STANDARDS OF PRACTICE

1. American Association of State Highway and Transportation Officials
2. The Design Manual for Roads and Bridges (DMRB)
3. Manual of Contract Documents for Highway Works (MCHW)
4. Routine and Winter Service Code
5. Technology Management and Maintenance Manual (TMMM)
6. Traffic Systems and Signing Plans Registry (TSS)
7. American Society for Testing and Materials (ASTM)
8. ISO 22242:2005(en): Road construction and road maintenance machinery and equipment — Basic types — Identification and description
9. Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14, UNITED STATES DEPARTMENT OF TRANSPORTATION, Federal Highway Administration
10. Permanent International Association of Road Congresses (PIARC), Road Safety Manual (RSM)
11. Ministry of Transportation/ Department of Transportation
12. US Department of Transportation (DOT), 23 CFR PART 625, Design Standards for Highways
13. US Department of Transportation (DOT), Highway Design Manual
14. US Department of Transportation (DOT), FAA AC 150/5300-13, Airport Design
15. US Department of Transportation (DOT), FAA AC 150/5390-2, Heliport Design
16. US Department of Transportation (DOT), Highway Functional Classification Concepts, Criteria and Procedures
17. US Department of Transportation (DOT), Federal Highway Administration (FHWA), Gravel Roads, Construction and Maintenance Guide
18. National Highway Authority
19. Asphalt Institute, MS-2, Asphalt Mix Design Methods
20. National Environmental Policy Act
21. Noise Control Act
22. Oglesby Clarkson H., “Highway Engineering”, John Wiley & Sons Inc., U.S.A., 1975.
23. Zhang, Y., Wu, D.Q. General applications of the semi-rigid pavement in South East Asia. Int. J. Pavement Res. Technol. 13, 296–302 (2020). https://doi.org/10.1007/s42947-020-0114-1
24. Perpetual Pavement A Boon for the Indian Roads, Chandan Basu, Atasi Das, Pavanaram Thirumalasetty, Tanmay Das
25. AASHTO Guide for Design of Pavement Structures, 1993

DEFINITION
A pavement (paved way) is an artificially covered/ paved durable surface. The primary purpose of a pavement is to provide a smooth surface, to prevent/ minimise moisture penetration and to transfer loads from pedestrian or vehicluar movements to underlying ground, which could be made of natural soil, stabilised soil, or compacted layers of soil, compacted layers of engineered fills, or compacted layers of aggregates. A side walk, bike track or a footpath for pedestrians or bikes can also be called a pavement.

An unpaved road or unpaved path, or gravel road is a low volume road with no artificially paved surface. In order to maintain a gravel road properly, three basic elements must be considered, such as a crowned driving surface, a shoulder area that slopes directly away from the edge of the driving surface, and swales or ditches on both sides. Gravel roads pose an uncomfortable driving experience, because of the distortion in the road surface, which can be avoided by operating a motorgrader not too fast, and using the moldboard of the motorgrader at the appropriate angle.

A Highway is a busy road with many lanes. It is a public road that could have limited/ restricted access (thru ramps only) and it also could have tolls. They do not serve adjacent lands/ properties. Interstate, Freeway, Motorway, Expressway are all highways. They're wide and have high speed limits, and thus decreased the travel time. They prohibit some slower modes of transport such as bicycles or horses. Highways are usually the quickest route for driving between one city and another.

A Roadway is a way, long but very narrow as compared to the length, with a smoothed, or compacted or paved surface, made for traveling by motor vehicle, carriage, providing passage from one place to another. A Roadway can be a Arterial or a Collector or a Local Road or a Street.

CLASSIFICATION
A. Classification by Functionality: There are different names given to pavements, in different countries, based on their functionality, speeds, volume of traffic or trips they accomodate, the most common being as follows;

1. Interstate: It is a highway or a series of highways which connect states or provinces. The interstate system is composed of highways, but not all highways are a part of the interstate.
2. Freeway/ Expressway: It is a highway with no toll. Other names can be Motorway, Autoroutes, Autobahnen etc.They have directional travel lanes are usually separated by some type of physical barrier. They connect major cities and urban centers. Motorways can be used and have been used as aircraft landing strips in emergencies by removing some previously planned removable medians.
3. Tollway/ Turnpike/ Tollway: It is a highway for the use of which a charge is made.
4. Arterial: It is not a highway. It is a roadway to serve major centers of metropolitan areas, providing a high degree of mobility in urban areas, and can also provide mobility through rural areas. They serve demand for intra-area travel between the central business district and outlying residential areas. They carry high proportion of total urban travel on minimum of mileage. They are not completely access controlled and may have at grade intersections. Arterials can be Principal Arterials or Minor Arterials. Minor Arterials provide service for trips of moderate length, serve geographic areas that are smaller than their higher Arterial counterparts and offer connectivity to the higher Arterial system. Major and Minor Arterials can also be Urban Arterials or Rural Arterials. Major Arterials maybe divided or not, but Minor Arterials are always not divided.
5. Collector: It is not a highway but a roadway. Collectors serve a critical role in the roadway network by gathering traffic from Local Roads and funneling them to the Arterial network. Collectors can be Major and Minor also. Major Collectors offer more mobility and Minor Collectors offer more access. They are also known as collector or feeder roads.
6. Local Road: They are not intended for use in long distance travel. They provide direct access to abutting land. Bus routes generally do not run on Local Roads. They are often designed to discourage through traffic.
7. Street: It is a roadway in the built environmemt with dwellings on both sides, on which people may freely assemble, interact, and move about.

B. Classification by Composition: The fundamental difference between types of pavements (flexible or rigid pavement) is due to the the design basis used for load distribution over the subgrade. A comparison between different types of pavements can be seen in the downloads section at the bottom. Pavements can be categorized into the following groups.

1. FLEXIBLE PAVEMENTS: Flexible pavement is surfaced with bituminous (or asphalt) materials, also called Hot Mix Asphalt (HMA) pavement. It has a layered system where better materials are used in the top most layer, where surface stress conditions are caused by traffic wheel loads. Load-distributing characteristics of a layered system protect each underlying layer. Each progressive layer is better than the lower layer. All the layers are meant to ultimately protect the subgrade from compressive shear failure. Pavement design is greatly influenced by the subgrade strength. It reflects the deformations of subgrade and subsequent layers on the surface. Various types are explained below;
1. Conventional Layered Pavement: While some layers can be omitted, the typical Layers are as follows;
   1. Seal Coat/ Chip Seal (optional) - It is a thin asphalt surface treatment, made of crushed aggregates (chips) embedded in asphalt binders.
   2. Asphaltic Wearing Course (HMA) - It resist distortion under traffic. Provides smooth, uniform, and skid resistant riding surface. Waterproof to protect the entire pavement from the weakening effects of water.
   3. Tack Coat
   4. Asphaltic Binder Course (HMA) - HMA is too thick to be compacted in one layer (if the binder course is more than 3” it is placed in two layers). Provides more economical design, since binder course generally consist of larger aggregates and less asphalt and doesn’t require high quality.
   5. Prime Coat - Minimizes flow of asphalt cement from the asphalt concrete to the aggregate base. Fills the surface voids and protect the subbase from weather. Stabilizes the fines and preserve the subbase material. Promote bonding to the subsequent pavement layer.
   6. Base Course - It usually consists of high-quality aggregates, such as crushed stone, crushed slag, gravel and sand, or combinations of these materials. The specifications and compaction requirements for base materials are usually more stringent than those for the lower-quality subbase materials.
   7. Sub-base Course (optional - A subbase layer is typically included when the subgrade soils are of very poor quality and/or Suitable material for the base layer is not available locally, and is, therefore, expensive .)
   8. Compacted Subgrade
   9. Leveled Natural Subgrade
2. Full Depth Asphalt Pavement: This type is normally used when local rock materials (aggregates) are scarce. They have no permeable granular layers to entrap water and impair performance. moisture contents do not build up in subgrades under full-depth asphalt pavement structures as they do under pavements with granular bases. Time required for construction is reduced. They are less affected by moisture or frost. Typical layers are as follows;
   1. Asphaltic Wearing Course
   2. Tack Coat
   3. Asphaltic Binder Course
   4. Compacted Subgrade
   5. Leveled Natural Subgrade
3. Contained Rock Asphalt Mat (CRAM): This type reduces vertical compression strain on the on the subgrade. Horizontal tensile stresses on the aggrgate is also reduced. Ultimately there are lesser stresses and strains on the wearing course. An additional asphalt layer is placed below the untreated granular materials but above the subgrade. Typical layers are as follows;
   1. Dense Graded Asphalt Wearing Course
   2. Dense Graded Aggregate layer
   3. Open Graded Aggregate layer
   4. Modified Dense Graded Asphalt layer
   5. Compacted Subgrade
   6. Leveled Natural Subgrade
4. Perpetual Pavement: It is a also a full depth asphalt pavement but uses many layers of deep-strength HMA. Traditionally, conventional flexible pavements are designed for a 20-year life, whereas perpetual pavements (PP) are expected to perform for 50 years or more, without requiring major structural rehabilitation or reconstruction. Two PP sections of Interstate 40 in Oklahoma City are more than 33 years old (built in 1967) and are still in excellent condition. These sections, which support 3 to 3.5 million ESALs per year, have been overlaid but the base and intermediate courses have lasted since construction without any additional work. Typical layers are as follows;
   1. Top HMA layer - This is the top layer is rut resistant designed specifically to resist surface-initiated distresses such as top-down cracking and rutting.
   2. Intermediate HMA layer - Dense Graded Aggregate layer carries most of the traffic load. It must be stable as well as durable. Stability can best be provided by using stone-on-stone contact in the coarse aggregate and using a binder with the appropriate high-temperature grading.
   3. Bottom HMA layer/ Base layer - It is designed specifically to resist fatigue cracking in the following ways.
      1. The total pavement thickness can be made great enough such that the tensile strain at the bottom of the base layer is insignificant.
      2. the HMA base layer could be made using an extra-flexible HMA. This can be most easily accomplished by increasing the asphalt content.
   4. Compacted Subgrade
   5. Leveled Natural Subgrade
2. SEMI-RIGID PAVEMENTS (SRP): It uses bonded materials like the pozzolanic concrete, lean cement concrete, or soil cement in the base course or sub-base course layer. The pavement layer has considerably higher flexural strength than the common flexible pavements, combining the flexibility from asphalt component and the rigidity from cement constituent. Commonly used in road junctions, airport aprons, bus depots and heavy loading yards.
3. RIGID PAVEMETNS: Rigid pavements are composed of a Plain or Reinforced Concrete surface course. Its structural strength is provided by the pavement slab itself by its beam action. Concrete is placed directly on the prepared subgrade, or a single layer of aggregate material (or stabilised earth material) on the subgrade. While horizontal control joints can be minimised by using reinforced concrete, longituninal control joints must be provided between driving lanes. Typical layers are as follows;
1. Concrete Surface
2. Granular Base Course or stabilised earth (optional)
3. Sub-Base Course or stabilised earth (optional)
4. Compacted Subgrade
5. Leveled Natural Subgrade
Various types are explained below;
1. Jointed plain concrete pavement (JPCP): JPCP requires extensive control joints, closely spaced, which contributes a lot to the roadway noise. Dowels or keyed (tongue and groove) joints or combination of both are used for load transfer across joints.
2. Jointed reinforced concrete pavement (JRCP): Steel reinforcement in the form of wire mesh or rebar in combination with dowels are used to minimise the number of control joints. Reinforcements do not contribute a lot to the structural capacity of the pavement, but only reduce the number of control joints, and keep the pavement togather if cracking occurs.
3. Continuous reinforced concrete pavement (CRCP): Under the premise that joints are the weakest links in rigid pavements, this type of construction eliminates the need for transverse control joints. Longitudinal control joints with dovels are still required, but edges of the pavement are still vulnerable to cracking (punch out) due to moisture infiltration leading to erosion of base/subbase support.
4. Pre-stressed concrete pavement (PCP): Pre-application of compressive stress to precast concrete reduces the tensile stresses caused by traffic. This method reduces the thickness, reduces maintenance requirements, reduces cracking, reduces costs, and increases pavement life. It is preferred for airport pavements. Fewer transverse joints may be provided as per design, while longitudinal control joints with dovels are still required.
4. COMPOSITE PAVEMENTS: ...

C. Classification by Design Methods: Pavements perform in response to 3 primary influences:

1. Traffic
2. Environment
3. Pavement (materials and thicknesses)

There are various methods to design the flexible pavement, some of which are given below;

1. Empirical methods: This approach uses the results of experiments and experience to ascertain relationships between input variables (observed/ measurable) and outcomes (pavement performance. Mostly commonly used Empirical equations are as follows
   1. AASHTO 1993 Method: It is the most common empirical design method in use today. The current AASHTO Design Guide is based on methods that evolved from the AASTHO Road Test (1958–1961) in Iowa, USA. Due to the inherently empirical nature, pavement is inherently over-designed for strength. Other performance measures, such as rutting, thermal cracking, and faulting are not addressed.
   2. Group Index Method: It is based on the physical properties of the soil sub-grade. To design the thickness of the pavement Group Index Value (GI) of the soil is established. Use the design charts thickness of the pavement and layers is determined.
   3. CBR Method: Similar to the AASHTO Method, the California method relates pavement structure (in the form of an equivalent thickness of gravel) to applied loads and subgrade support.
2. Mechanistic-empirical (M-E) methods: Since AASTHO Road Test (1958–1961) in Iowa, road speeds have changed, tire pressures have changed and traffic volumes have increased tremendously. It can be used for both existing pavement rehabilitation and new pavement construction. It accommodates changing load types. It can better characterize materials. It accommodates environmental and aging effects on materials. The M-E Pavement Design Guide follows the following steps;
   1. The temperature and moisture profiles are generated for the conditions at time = t (Environment)
   2. The spectrum of traffic loadings in the next time increment (Δt)
   3. Elastic properties and thickness of each layer (E, µ, h) are defined
   4. Structural analysis is performed to estimate critical stresses and strains within the structure
   5. An ancillary analysis is performed to determine the non-load-related stresses and strains
   6. Incremental distresses (for such as rutting, faulting, transverse cracking, roughness) are computed based on the critical stresses and strains. This is done using emperical methods
   7. Changes in initial material parameters (E, µ) resulting from the computed incremental damage are estimated.
   8. The time scale is incremented to t = t0 + Δt, and the cycle repeated
3. Mechanistic method: It simply means that a model is used to calculate the reaction of the pavement to traffic loads, and no empirical methods are used.
4. Analytical or Mathematical methods:

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