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.

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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

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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،

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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.