Transport Chapt 5_handout

7/30/2019 Transport Chapt 5_handout

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Chapter V

TRAFFIC CONTROLS

Tewodros N.

[email protected]
http://www.tnigatu.wordpress.com/http://www.tnigatu.wordpress.com/


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Lecture Overview Traffic markings

Longitudinal markingsTransverse markings

Object markers and delineator

Traffic signsRegulatory signs.

Warning signs.

Guide signs.

Traffic signals Signal Timing Design- Webster method

Transport Engineering School of Civil andTewodros N. Environmental En ineerin


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Traffic ControlsTraffic control devices are the media by

which traffic engineers communicate withdrivers.

Traffic Control devises broad categorized tothree

Traffic markings

Traffic signsTraffic signals



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Traffic ControlsTraffic control devices are the media by which traffic

engineers communicate with drivers.Traffic Control devises broad categorized to three

Traffic markings

Traffic signsTraffic signals

Traffic engineers design traffic control devices that communicate

uncomplicated messages clearly, in a way that encourages properobservance.



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Traffic Controls ContTraffic control messages are conveyed

through

Color

Shape

Pattern

Legend



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Traffic Markings

Markings are applied to the roadway surface

using a variety of materials, the mostcommon of which are paint andthermoplastic.

Longitudinal markings

Transverse markings

Object markers and delineators



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Traffic Markings Cont

Longitudinal markings

Are those markings placed parallel to the directionof travel.

Provide guidance for the placement of vehicleson the traveled way cross-section and basictrajectory guidance for vehicles traveling alongthe facility.

Centerlines,

Lane lines, andPavement edge lines



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Centre line

Separates the opposing streams of traffic and facilitates theirmovements. Are those markings placed parallel to the direction oftravel.

May be marked with either single broken line, single solid line,double broken line, or double solid line depending upon the road

and traffic requirements.



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Lane Markings

Is a single white dashed line separating lanes of traffic in the samedirection.

MUTCD standards require the use of lane markings on all free-ways and Interstate highways and recommend their use on allhighways with two or more adjacent traffic lanes in a single

direction.



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Edge Markings

Indicate edges of rural roads which have no curbs to delineate the limitsup to which the driver can safely venture.

Should be preferably light reflective, so that they will be visible duringnight also.

Warning lines

warn the drivers about the obstruction approaches. Are marked on horizontal and vertical curves



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Traffic Markings ContTransverse Markings

Any and all markings with a componentthat cuts across a portion or all of thetraveled way.

All transverse markings areCrosswalk Markings

Parking Space Markings

Directional arrows

Word and Symbol Markings



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Traffic Markings ContCrosswalk Markings

Is recommend that crosswalks be marked atall intersections with "substantial" conflictbetween vehicles and pedestrian exists.



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Traffic Markings ContParking Space Markings

Are not purely transverse, as they contain bothlongitudinal and transverse elements.Used to encourage efficient use of parking spaces.



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Traffic Markings ContDirectional arrows

Used to guide the drivers in advance over the correctlane to be taken while approaching busy intersections.

Word and Symbol Markings

Word markings include "ONLY" used in conjunction with laneuse arrows, and "STOP" which can be used only in conjunction

with a STOP line and a STOP sign.



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Traffic Markings ContObject Markers

Are used to denote obstructions either or adjacentto the traveled way.


Type 1 Object Markers

Type 2 Object Markers Type 3 Object Markers


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Traffic Signs

Regulatory signs.

Warning signs.

Guide signs.



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Traffic Signs ContRegulatory signs

Shall be used to inform road users of selected traffic laws orregulations and indicate the applicability of the legalrequirements.

Regulations may relate to right-of-way, speed limits, laneusage, parking, or a variety of other functions.

Right of way seriesSpeed seriesMovement series

Parking seriesMiscellaneousPedestrian series



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Traffic Signs ContWarning Signs Call attention to unexpected conditions on or adjacent to a highway or street

and to situations that might not be readily apparent to road users. Most warning signs are diamond-shaped, with black lettering or symbols

on a yellow background.

Changes in horizontal alignment

Intersections

Advance warning of control devices Converging traffic lanes

Narrow roadways

Changes in highway design

Grades

Roadway surface conditions

Railroad crossings



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Traffic Signs ContGuide/Informative/ Signs

Provide information to road users concerning destinations,available services, and historical/recreational facilities. Familiar or regular users of a route will generally not need to use

them. Clarity and consistency of message is the most important aspect

of guide signing.



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Traffic signalObjectives

To reduce the average delay of all vehicles and theprobability of accidents.

Minimize the possible conflict points.

Types of Signal Operation

Pre timed operationFull actuated operation

Semi-actuated operation.Computer control.



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Traffic signal ContComponents of a Signal Cycle Cycle:-is one complete rotation through all of the indications provided. Cycle length:-is the time (in seconds) that it takes to complete one full

cycle of indications. Interval:-is a period of time during which no signal indication

changes.

Change interval (yellow) :-is the "yellow" indication for a given movement. Clearance interval (all red ):-is also part of the transition from "green" to

"red" for a given set of movements. Green interval:-Each movement has one green interval during the signal

cycle. Red interval:- Each movement has a red interval during the signal cycle.

Phase:-A signal phase consists of a green interval, plus thechange and clearance intervals that follow it.



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Traffic signal ContSignal Timing at Isolated Intersections

An isolated intersection is one in which the signal time isnot coordinated with that of any other intersection andtherefore operates independently.

Yellow IntervalThe main purpose of the yellow indication after the green is

to alert motorists to the fact that the green light is about tochange to red and to allow vehicles already in theintersection to cross it.

Is the time period that guarantees that an approachingvehicle can either stop safely or proceed through theintersection without speeding.



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Traffic signal ContFor the dilemma zone to be eliminated the distance X

o

should be equal to the distance Xc.Xc= uo (min) (W + L)For vehicles to be able to stop, however,

For the dilemma zones to be eliminated, Xo

mustbe equal to Xc.

uo (min) (W + L)

min =



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Traffic signal ContIf the effect of grade is added,

min =

Webster method



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ExampleFigure and table shown on next slide shows peak

-

hour volumes for a major intersection on an arterialhighway. Using the Webster method, determinesuitable signal timing for the intersection using a

four

phase system and the additional data given inthe figure. Use a Yellow interval of 3sec.


East Approach West Approach South Approach North Approach

Lane1

2

31

2

31

2

31

2

3PHV 222 467 467 128 321 321 109 75 25 206 100 128


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