Lecture 01 7
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
In this lecture; --------------------- 1- Definitions and concepts. 2- Trip stages. 3- Accessibility and mobility. 4- Highway functional classification A - Urban and rural areas B – Functional categories 5- Highway classification in Iraq
Functional Classification of Highways -
The information listed in this lecture is mainly taken from the U.S reference entitled A Policy on Geometric Design of Highways and Streets (AASHTO, 2011) and Traffic and Highway Engineering (Garber and Hoel, 2009).
1- Definitions and Concepts.
The classification of highways into different operational systems, functional classes,
or geometric types is necessary for communication among engineers,
administrators, and the general public.
Different classification schemes can be applied for different administrative, planning
and design purposes in both rural and urban regions. Following are typical
examples:
- Classification of highways by design types based on the major geometric features
(e.g., freeways and conventional streets and highways) is the most helpful one for
highway location and design procedures.
- By route numbering (e.g., U.S., State, County) is the most helpful for traffic
operations.
- By administration (e.g., National Highway System or Non-National Highway
System) is used to denote the levels of government responsibility and financing of
highway facilities.
Lecture 01 8
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
A complete functional design system
provides a series of distinct travel
movements. The six recognizable stages in
most trips include:
a- main movement,
b- transition,
c- distribution,
d- collection,
e- access, and
f- termination.
For example, Fig. 1 shows a hypothetical
highway trip using a freeway, where the
main movement of vehicles is
uninterrupted, high-speed flow.
- By paving materials (e.g., asphalt pavement (flexible) and concrete pavement
(rigid)).
- By number of lanes (e.g., two lanes and multi-lanes highways). This is adopted in
the Highway Capacity Manual (HCM) in determining the LOS of highways.
- Finally, functional classification, the grouping of highways by the nature of
service they provide. For example, arterials, collectors and local roads. This
classification was developed for transportation planning purposes.
2- Trip Stages
Lecture 01 9
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
When approaching destinations from the freeway, vehicles reduce speed on
freeway ramps, which act as transition roadways. The vehicles then enter moderate-
speed arterials (distributor facilities) that bring them nearer to the vicinity of their
destination neighborhoods. They next enter collector roads that penetrate
neighborhoods. The vehicles finally enter local access roads that provide direct
approaches to individual residences or other terminations. At their destinations the
vehicles are parked at an appropriate terminal facility.
The conflict between serving through
movement and providing access to trip
origins and destinations necessitates the
differences and gradations in the various
functional types. See the adjacent figure.
Regulated limitation of access is needed
on arterials to enhance their primary
function of mobility. Conversely, the
primary function of local roads and
streets is to provide access, which
causes a limitation of mobility.
The two major considerations in classifying highway and street networks
functionally are access and mobility. Accessibility usually refers to the ability to
reach desired goods, services, activities and destinations, while mobility usually
refers to the movement of people or goods.
3- Accessibility and Mobility
Lecture 01 10
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
Urban and rural areas have fundamentally different characteristics with regard to
density and types of land use, density of street and highway networks, nature of
travel patterns, and the way in which these elements are related. Consequently,
urban and rural functional systems are classified separately.
Urban areas are those places within
boundaries set by the responsible
State and local officials having a
population of 5,000 or more.
4- Functional Classification of Highways
This section contains definitions and characteristics of highway facilities in urban
and rural regions based on their functional classifications.
A- Urban and Rural Areas
Rural areas
are those areas outside the boundaries of urban areas.
Lecture 01 11
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
B- Functional Categories The roads making up the functional systems differ for urban and rural areas. The
hierarchy of the functional systems consists of principal arterials (for main
movement), minor arterials (distributors), collectors (major and minor), and local
roads and streets.
Figure 3 below shows the typical functional classification decision tree.
Lecture 01 12
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
Highways within this system are divided into three subclasses: (a) interstate, with fully-controlled access and grade separated interchanges; (b) freeways and expressways, which have controlled access but may also include at-grade intersections; and (c) other principal arterials (with partial or no controlled access).
In urban regions, this system of highways serves the major activity centers and consists mainly of the highest-traffic-volume corridors. In contrast, in rural areas it serves all highway trips between urbanized areas and a high percentage of trips between small urban areas with populations of 25,000 or more.
There are several travel characteristics that are also key in assigning functional
classifications to roadways. Some of them are shown in Table 1 below.
1) Principal arterials
Lecture 01 13
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
Minor arterials interconnect the principal arterial
system. In an urban context, they provide intra-
community continuity and may carry local bus
routes. They usually provide service for trips of
moderate length.
In rural areas, minor arterials link cities and
larger towns (and other major traffic generator
areas such as major resorts.
The main purpose of collector streets is
to collect traffic from local streets in
residential areas or in CBDs and convey
it to the arterial system. Thus, collector
streets usually go through residential
areas and facilitate traffic circulation
within residential, commercial, and
industrial areas.
Generally, Major Collector routes are
longer in length; have lower connecting
driveway densities; have higher speed
limits; have higher AADT volumes; and
may have more travel lanes.
2) Minor arterials 3) Major & minor collectors
Lecture 01 14
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
This system consists of all other streets
that are not included in the three
systems described earlier.
The primary purposes of these streets
are to provide access to abutting land
and to the collector streets. Through
traffic is discouraged on these streets.
4) Local roads 5- Highway classification in IRAQ
According to the Iraqi Highway Design Manual (SCRB, 2005), the system of highways
in Iraq can be generally classified as follows:
1) Primary system
Highways of international importance (the main highways connecting main cities)
and highways of special importance should form the primary system of national
highways. These highways are to be designed to the highest standard.
2) Secondary system
Highways connecting major cities of economic or other importance and highways
connecting agricultural, commercial, recreational or tourist area should form the
secondary system of highways.
3) Tertiary system
Highways of district and local importance should form the tertiary system.
Lecture 01 15
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
:منقول من الموقع االلكتروني للهيئة العامة للطرق و الجسور العراقية
تطورت شبكة الطرق البرية العامة من طرق القواف�ل الترابي�ة عن�د اول تش�كيل الحكوم�ة العراقي�ة
س�ور الحديث�ة ف�ي كاف�ة انح�اء شبكة م�ن الط�رق المبلط�ة الحديث�ة م�ع انش�اء ع�دد كبي�ر م�ن الجالى
.القطر
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) وطري�ق اب�و غري�ب الس�ريع) 1(طريق المرور السريع رقم ( الطرق السريعةكم تضم 42000
الت�ي ت�ربط ب�ين والط�رق الثانوي�ةالتي تربط مراك�ز المحافظ�ات والمناف�ذ الحدودي�ة شريانيةوال،
الت��ي ت��ربط ب��ين المجمع��ات الس��كنية ف��ي الق��رى واالري��اف والط��رق الريفي��ةاالقض��ية والن��واحي
بالطرق الثانوية والشريانية، والجدول االتي يبين اطوال شبكة الط�رق المبلط�ة باص�نافها المختلف�ة
- :2004ية عام لغا
ان الهيئة العامة للطرق والجسور مستمرة في خطة انشاء الطرق وخاص�ة الريفي�ة منه�ا لالقت�راب
م�ن كثاف�ة 2ك�م/ نس�مة 100لك�ل ( للكثاف�ة الس�كانية " من المعايير الدولية ف�ي اط�وال الط�رق تبع�ا
) .من الطرق 2كم/ كم 1السكان تحتاج الى
على نهري دجل�ة والف�رات وتفرعاتهم�ا والودي�ان وخط�وط " بتاثا" جسرا 1200كما تضم الشبكة
انش��اء الجس��ور الجدي��دة واس��تبدال ، والهيئ��ة مس��تمرة ف��ي" عائم��ا" جس��را 60اض��افة ال��ى الس��كة
. الجسور العائمة باخرة ثابتة
)كم ( الطول صنف الطريق ت
1084 طرق المرور السريع .1 11000 الطرق الشريانية .2 15200 الطرق الثانوية .3 3700 الطرق الريفية .4 11000 الطرق الحدودية .5
Lecture 01 16
Highway Eng. Highway Functions 14 –15
Dr.Firas Asad
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Highway classification is the first step in highway
design process.
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