crosss section 2011

8/3/2019 Crosss Section 2011

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NS 3493 HIGHWAY ENGINEERING Semester 1, 2011/2

epared/Edited by Ron Aldrino

PREPA RED B Y

RO N A L D RIN O C H A N

Cross Sections

Reflection

Being happy with less is what makes a great humanbeing, not a big house with marble f loors, or

everyone knowing who you are.

~ Yanni

You will never be happy if you continue to search forwhat happiness consists of. You will never live if

you are looking for the meaning of life.

~ Albert Camus

Objectives

Identify cross section

components and design criteria.

What is Cross Section??

A cross section is a vertical plane (slice) taken at right

angles to the road control line showing the various

elements that make up the roads structure.

It is normally viewed in the direction of increasing

chainage.

Cross section of a road: main road situated outside towns and cities.Platform: horizontal surface raised above the surrounding ground.

Shoulder: space between the roadway and the ditch.Median strip: separation between two roadway.Carriageway: central part reserved for vehicle traffic.Ditch: channel that carries away water.

Subgrade: upper surface of a road.Base course: middle surface of a road.Subbase: lower surface of a road.

Typical Road Cross Section


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Background

The cross section of a road includes some or all ofthe following elements: Traveled lane (the portion of the roadway provided for the

movement of vehicles, exclusive of shoulders)

Roadway (the portion of a highway, including shoulders, providedfor vehicular use)

Median area (the physical or painted separation provided on dividedhighways between two adjacent roadways)

Bicycle and pedestrian facilities

Utility and landscape areas

Drainage channels and side slopes

Clear zone width (i.e., the distance from the edge of the traveledway to either a fixed obstacle or nontraversable slope)

Background

Considered as a single unit, all these cross section

elements define the highway right of way.

The right of way can be described generally as thepublicly owned parcel of land that encompasses all the

various cross section elements (see Figures 6.1 and 6.2).

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Figure 6.1 Two lane rural highway cross section design features and terms.

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Figure 6.2

Urban highway cross section

design features and terms.

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Existing Layout

(Urban)

Proposed Layout

(Urban)

Proposed Layout

(Pub. Transport

(Urban)

In selecting the appropriate cross section elements anddimensions, designers need to consider a number of

factors, including the following: Volume and composition (percent trucks, buses, and recreational

vehicles) of the vehicular traffic expected to use the facility

The likelihood that bicyclists and pedestrians will use the route

Climatic conditions

The presence of natural or human made obstructions adjacent to theroadway (e.g., rock cliffs, large trees, wetlands, buildings, powerlines)

Type and intensity of development along the section of the highwayfacility that is being designed

Safety of the users


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Cross Section Elements

Travel Lanes

The number of lanes needed for a facility is usuallydetermined during the concept stage of projectdevelopment.

Function: guidance to drivers and vehicle support Pavement types: high (modern standards),

intermediate (surface treatments), and low (unpaved) Selection criteria:

Traffic volume and composition Soil characteristics Past performance in area Availability of materials Initial cost Maintenance cost Overall life cycle cost

Travel Lane Cross Slope

Slopes are important to remove water from the roadway.Inadequate drainage becomes apparent after heavy rain.

The trade-off is draining away water, which suggestssteeper, and keeping vehicles from sliding, whichsuggests flatter.

Two-Lane Highways - Slopes generally fall away fromthe centerline on both directions.

Divided Roadways - Each roadbed is slopedindividually and may be crowned separately as well

(especially on divided highways).

Source:A Policy on Geometric Design of Highways and Streets (The Green Book). Washington, DC.

American Association of State Highway and Transportation Officials, 20 01 4th Ed.

Cross Slope

Drivers barely perceive cross slopes up to 2 %; 1.5 to

2 % are common cross slope values.

Higher values may be unsafe.

AASHTO recommends

High 1.5 to 2%

Intermediate 1.5 to 3%

Low 2 to 6%


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Lane Width

The width of travel lanes is limited by the physicaldimensions of vehicle, average daily traffic volume ofcommercial vehicles and the requirements for

overtaking and passing to a range between 2.7 and3.6 m (9 and 12 ft).

Generally, as the design speed of a highway increases,so must the lane width to allow for the lateral movementof vehicles within the lane.

Although lane widths of 3.6 m are desirable on bothrural and urban facilities, there are circumstances thatnecessitate the use of lanes less than 3.6 m wide.

Lane Width

In urban areas where right of way and existing

development become stringent controls, the use of

3.3 m lanes is acceptable. Lanes 3.0 m wide are acceptable on low speed facilities.

Lanes 2.7 m wide are appropriate on low volume roads

in rural and residential areas.

Median

An important consideration in the design of anymultilane highway is whether to provide a median and,if one is provided, what the dimensions should be.

The primary functions of highway medians are to:

Separate opposing traffic flows

Provide a recovery area for out of control vehicles

Allow space for speed changes and left turning and U-turningvehicles

Provide width for future lanes (particularly in suburban areas)

Provide a space for landscape planting that is in keeping with

safety needs and improves the aesthetics of the facility

Provide a space for barriers.

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A landscaped median.

Two way left turn lanes improve safety

and efficiency for vehicular traffic but

do not afford a safe refuge for pedestrians

Median

Depending on agency practice and specific locationrequirements, medians may be depressed, raised, or

flush with the surface of the traveled way. Medians should have a dimension that is in balance with

the other elements of the total highway cross section.

The general range of median widths is from 1.2 m (4 ft),usually in urban areas, to 24 m (80 ft) or more, in ruralareas.

An offset of at least a 500 mm (1.5 ft) should beprovided between any vertical element located withinthe median, such as a curb or barrier, and the edge of theadjacent traveled lane.

Shoulders

The roadway shoulder lies between the outer edge of thetravel lane and the inside edge of the ditch, curb, slope

or median (in divided roadways). Shoulders are slopedso that water runs off from the travel lane.

Functions: Structural support is given to the pavement

Space is provided to escape potential accidents

Space is provided for emergency stopping free of the trafficlane

Space is provided for pedestrian/bike use

Turning/Passing at intersections

Lateral clearance is provided for signs and guardrails


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Geometry

o Paved (bituminous, concrete)/Unpaved (earth, turf, gravel)

o AASHTO recommends 3.0 m widths as normal on freeways

and minimum of 0.6 m on lowest highways.

o At least 1.2 m should be available from the edge of theroadway to a roadside barrier.

o In general,

asphalt or concrete-paved shoulders are sloped from 2 to 6%,

gravel shoulders from 4 to 6% and

turf shoulders at about 8%.

Shoulder widths are usually determined by the trafficvolume, safety and the percent of heavy vehicles.

Shoulders

(a) Gravel (b) Paved

(c) Concrete (d) Grass with sidewalk

Various shoulder treatments

Road Reserve

Road Reserveis that parcel of land dedicated or

gazetted to the roadrange from 14m wide suburban to

up to 200m or more in rural areas

Batters

cuttings at edge of formation to meet natural surface. Dictated

by

Soil type and stability

Depth of cut/fill

Appearance

Economics

Environmental reasons

If cut/fill 3m slope dictated by material stability and may vary

from 2:1 to 0.25:1.

In deep cuts geological investigation required prior to design.

Batter Benches (Berms)

On high batters >8m consider benches

reduce scouring

provide more stable batter

Reduce rock fall problems

Reduce water into table drain

Assist vegetation re-establishment

Provide maintenance access

Reduce batter maintenance

Allow steeper batter slopes

Benches should be 3-5m wide (5m for machines) and graded to

remove water away from roadmax crossfall 10%


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Verge

between shoulder and the drain

In urban areas it would include the kerb, nature strip and path

If provision for guard railing2m wide required

In cutting 2m wide desirable @ 6:1 grade for safety

Depending on costconcrete kerb may be required for deep

cuttings

In deep cuttings with unstable materia l verge may be widened to

collect fallen material to keep shoulders clear

Verge

Marginal strip

Is a narrow pavement strip attached to both edges of a

carriageway.

It is paved to the same standard as then traffic lanes.

For divided roads, the marginal strips are provided on

both sides of the carriageways.

The marginal strip is included as part of the shoulder

width

Marginal Strip

Curbs

Curbs can serve some or all of the following functions:

Drainage control

Roadway edge delineation

Right of way reduction

Aesthetics

Delineation of pedestrian walkways

Reduction of maintenance operations

Assistance in roadside development.

Two types of curbs: barrier and mountable.

Barrier type curbs are not, however, recommended forprojects with design speeds above 65 km/h (40 mph).

Examples of barrier and mountable curbs.


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Traffic Barriers

Traffic barriers are used to minimize the severity of

potential accident involving vehicles leaving the

traveled way. Because barriers are hazard in themselves, emphasis

should be on minimizing the number of such

installations.

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Sidewalks and Pedestrian Paths

The safe and efficient accommodation of pedestriansalong the traveled way is equally important as theprovisions for vehicles.

Too often, pedestrians are a secondary consideration inthe design of roadways, particularly in suburban areas.

Although sidewalks are an integral part of city streets,they are much more rare in rural areas and providedonly sporadically in suburban areas, despite data thatsuggest that providing sidewalks along highways inrural and suburban areas results in a reduction inpedestrian accidents.

Sidewalks and Pedestrian Paths

Sidewalks can be located next to a planted strip or flush with the roadside edge.

The wider the sidewalk, the more room there is for street furniture,

trees, utilities, and pedestrians. Sidewalks can be built with a variety of shapes and materials.


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Pedestrian barriers can provide safety by separating pedestrian

and vehicular traffic.

Street trees and light fixtures are carefully lined to one side of the sidewalk to

provide the widest possible space for pedestrians

Accommodating Bicycles

Basically, there are five types of bicycle facilities: Shared lane - a "standard width" travel lane that both bicycles

and motor vehicles share Wide outside lane -an outside travel lane with a width of at

least 4.2 m (14 ft) to accommodate both bicyclists andmotorized vehicles

Bicycle lane - a portion of the roadway designated by striping,signing, and/or pavement markings for preferential or exclusiveuse by bicycles and/or other non motorized vehicles

Shoulder - a paved portion of the roadway to the right of thetraveled way designed to serve bicyclists, pedestrians andothers

Multiuse path - a facility that is physically separated from theroadway and intended for use by bicyclists, pedestrians, andothers

A multiuse path

The shoulders were specifically designed to accommodate bicycle traffic

Existing conditions.

Proposed continuous left turn lane design

Proposed continuous left and right turn lane design

Proposed channelized and raised median design

Computer visualization showing proposed design concepts


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Ditch - Developed primarily to collect and

move water. It is adjacent to a highway

and is usually identified as the roadside.

QUESTIONS ???
http://www.car-accidents.com/renault-crash-accidents.html

crosss section 2011

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