Intro to Traffic Engineering and Management

7/29/2019 Intro to Traffic Engineering and Management

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Intro to Traffic Engineering and Management 1

INTRODUCTION TO TRAFFIC ENGINEERING AND MANAGEMENT

1. Background

Transportation Engineering is a field or branch of civil engineering that deals with theapplication of technology and scientific principles to the

planning, functional design, operation, and management of facilities

for any mode of transportation in order to provide for the

safe, rapid, comfortable, economical, and environmentally compatible

movement of people and goods.

Traffic Engineering phase of transportation engineering that deals with the planning,

geometric design, and traffic operations of roads, streets, and highways, their networks,

terminals, abutting lands, and relationships with other modes of transportation.

Traffic Management is a term used to embody the activities undertaken by a highway

transportation agency to improve roadway system safety, efficiency, and effectiveness forboth providers and consumers of transportation services.

Two types of traffic management:

a. Conventional uses traditional traffic engineering tools or simple devices to regulate and

control traffic

b. Advanced relies more on advanced technology through the use of Intelligent Transport

Systems (ITS)

It is not uncommon to have a combination of conventional and advanced methods applied to

address traffic problems.


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2. Introduction to Traffic Flow Theory

A. Types of Flow

1. uninterrupted vehicles are not required to stop by any cause external to the trafficstream

2. interrupted vehicles are required to stop by cause outside the traffic stream, such as atraffic sign, or signal (usually at an at-grade intersection)

B. Basic Traffic Flow Variables

1. Speed (u) rate of motion (length of road/time), {kph, m/s}

2 principal average speeds:

1) Time mean speed (Spot speed)

arithmetic mean of the speeds of vehicles passing a point during a given interval oftime

common practice among traffic engineers to report the spot speed for a givenlocation

If 3 cars are traveling at constant speeds u1, u2, and u3:

ut = (u1 + u2 + u3)

2) Space mean speed (Harmonic mean speed)

average speed of vehicles occupying a given length of road at an instant of time

Considering again the 3 cars, the average travel time is;

=++= iuD

NuD

uD

uDt 13

1

321

The space mean speed is computed as:

==

iu

s

N

t

Du

1

Relationship of time mean speed and space mean speed:

s

ss

s

sst

u

u

u

uu

222

+=+

=


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Since 2

2

t

s

t

s

u

u

= , thent

tts

uuu

2

=

Thus, if we talk about a relationship between variables along a sketch of road:

q = kus , where us = space mean speed or average travel speed

2. Volume (q) number of vehicles passing at a point or section of roadway per lane fora given time period (number of vehicles/time), {vph, pcu/hr, veh/15-min}

Flow rate same as volume but less 1-hour period (usually expanded)

Time Volume Flow rate

8:00 8:15 400* 1,600**8:15 8:30

*400 vehicles in 15 minutes

**1,600 veh/hr

If N cars cross a line in time T, the flow is computed as:

q = N / T

Time Headway time interval between the passages of consecutive vehicles

Headway and flow are related as follows:

hh

Nh

N

T

Nq

i

N

i

i

1

1

1

1

====

=

Time headway inverse of volume (1/q)

Space headway inverse of density (1/k)

3. Density (k) number of vehicles in a given length of roadway or lane at an instant oftime (number of vehicles/length of roadway), {veh/km}

Time occupancy, Ot defined as the total time a detector is occupied divided by the

total time of observation

%100x

T

tO

i

t

=


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Ot= (d + l) k [for inductance loop detector]

Ot= l k [for ultrasonic detectors]

Space occupancy,Os total space occupied per unit length L

%100xL

lO

i

s

=

C. Lane Utilization

distribution of the total traffic volume to the individual lanes of multi-lanefreeways/highways (US HCM)

also referred to as lane distribution, traffic distribution or traffic split

normally measured in percentage (%) or ratio of total traffic

%100=Q

qp ii

Where i = number of lanes,qi = volume along lane i,

Q = total traffic volume,pi = usage for lane i

D. Weaving

The crossing of two or more traffic streams traveling in the same general direction along asignificant length of highway, without the aid of traffic control devices (US HCM)

Lane change maneuver employed in weaving Measured in terms of frequency over a defined length (e.g., frequency per 100 meters)

E. Level of Service (LOS)

Definition:

- a qualitative measure describing operational conditions within a traffic stream and theirperception by motorists and/or passengers (US HCM)

- Letter designation that describes a range of operating conditions on a particular type offacility

Measures of Effectiveness (MOE) parameter that describes the effectiveness or quality of service provided to the driver

or passenger


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Table 1: LOS for an intersection

LOS Stopped delay per vehicle (sec)

A 10.0B > 10.0 20.0

C > 20.0 35.0D > 35.0 55.0E > 55.0 80.0F > 80.0

Source: U.S. Highway Capacity Manual, 2000.

Table 2: LOS for an arterial (Urban Street Class I)

LOS Average Travel Speed (kph)

A > 67.2B > 54.4 67.2

C > 43.2 54.4D > 33.6 43.2E > 25.6 33.6F 25.6


Table 3: LOS for a freeway

LOS Max (v/c) Max service flow (pcu/hr/lane)

A 0.28 0.33 540 720B 0.47 0.55 900 1,200

C 0.66 0.75 1,260 1,650D 0.79 0.89 1,500 1,940E 1.00 1,900 2,200F Unstable Highly variable


Table 4: LOS for multilane highways.

(Freeflow speed = 60 mph)

LOSMax. Density

(pcpmpl)*Max. Density

(pcpkpl)**

A 11 7B 18 11C 26 16D 35 22E 40 25

* pcpmpl passenger car per mile per lane** pcpkpl passenger car per kilometer per laneSource: U.S. Highway Capacity Manual, 2000.


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Figure 1: LOS A

Figure 2: LOS B

Figure 3: LOS C


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Figure 4: LOS D

Figure 5: LOS E

Figure 6: LOS F


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Table 5: LOS for road section evaluation

Level of Service Volume / Capacity Ratio Description

A less than 0.20 free flow traffic

B 0.21 - 0.50 free flow traffic

C 0.51 - 0.70 moderate traffic

D 0.71 - 0.85 moderate / heavy traffic

E 0.86 - 1.00 heavy traffic

F greater than 1.0 forced flow, stop and go

Source: DPWH Highway Planning Manual

Figure 7: LOS and the fundamental traffic parameters q, u and k.

Table 6: LOS for a Walkways and Sidewalks

(Platoon-adjusted)

LOS Space (ft2/person) Flow Rate* (person/min/ft)

A > 530 0.5B > 90 530 > 0.5 3C > 40 90 > 3 6D > 23 40 > 6 11E > 11 23 > 11 18F 11 > 18

*Note: Rates represent average flow rates over a 5- to 6-minute period.Source: U.S. Highway Capacity Manual, 2000.

q

uA B

C

D

E

F

k1 k2 k3k4

k5


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3. Highway Capacity

A. Concepts

Capacity is the maximum number of vehicles that have a reasonable expectation of passing

over a given section of lane or roadway in one direction or in both directions during one hourunder prevailing road and traffic conditions.

Hourly capacity is influenced by the following factors:

Number of lanes; Carriageway width; Shoulder width; Gradients and their length; Truck and bus percentage of total traffic; Lateral obstructions on both or one side of the roadway; and

Roadside friction

The degree of roadside friction impact on road capacity:

None: Few or no buildings along the roadside;

Light: Buildings and/or road intersections along and close to the road, 100-200 metersbetween these objects, pedestrians and non-motorized traffic observed

occasionally;

Medium: Scattered roadside development, 50-100 meters between buildings and/or road

intersections, pedestrians and non-motorized traffic observed frequently;

Heavy: Continuous roadside development with less than 50 meters between buildings

and/or road intersections, pedestrians and non-motorized traffic tend to disrupt

the motor vehicle traffic and reduce travel speed to below 35 km/hr even at lowtraffic volume.

Based on studies undertaken by the Planning Services of the Dept. of Public Works and

Highways (1975-1977, 1979), the Philippine road capacities for varying roadway widths andflat terrain can be estimated as follows:

Table 7: Basic hourly capacities according to road type

Road Type Carriageway

Width (m)

Roadside

Friction

Basic Hourly Capacity

(in PCU in Both Directions)

Highway 4.0 None or Light 600

Highway 4.1 - 5.0 None or Light 1,200





Highway 2 x 7.0 None or Light 7,200 (Expressway)


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Table 7 (continued)Urban Street 6.0 Heavy 1,200

Urban Street 6.1 - 6.5 Heavy 1,600

Urban Street 6.6 - 7.3 Heavy 1,800

Urban Street 2 x 7.0 Heavy 6,700

Capacities under Philippine conditions are about 20 % higher than those reported in the U.S.Highway Capacity Manual of 1965. This could be due to the fact that the average passenger

car unit on Philippine roads is smaller than its U.S. counterpart and may also be attributed tothe behavior of local drivers (e.g., it is very common to drive quite close to the vehicle in front

and roads with 2 lanes per direction are effectively used as if there were 3 lanes instead). The

basic capacity reported in the U.S. HCM of 1965 is 2000 pcu/hr for both directions of a 2-lane, flat, 7.3-meter road without roadway friction. As can be seen from Table 1, the

Philippine corresponding capacity is 2400 pcu/hr.

For multi-lane highways in flat terrain, such as expressways, the lane capacities (if lane widthis at least 3.5 meters) are estimated as follows:

Table 8: Hourly capacities for multi-lane highways

No. of lanes per direction 2 3 4

Hourly capacity, pcu/lane 1,800 1,750 1,700

B.Passenger Car Equivalent Factors

The capacity is normally expressed in passenger car unit per hour (pcu/hr) and would dependon the so-called passengercarequivalent factors (PCEF) of the different vehicle classes that

compose the traffic. These factors express the impact of slow-moving vehicles and heavyvehicles interacting with gradients and length of gradients.

Table 9: PCEF values (DPWH, Highway Planning Manual, 2003

No. Vehicle Type PCEF

1 Motor tricycle 2.5

2 Passenger car 1.0

3-5 Passenger and goods utility and small bus 1.56 Large bus 2.0

7 Rigid truck, 2 axles 2.0

8 Rigid truck, 3 axles 2.5

9 Truck semi-trailer, 3 and 4 axles 2.5

10 Truck semi-trailer, 5+ axles 2.5

11 Truck trailers, 4 axles 2.5

12 Truck trailers, 5+ axles 2.5


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C. Level of Service

Following the definitions used by the DPWH Highway Planning Manual (2003) for theevaluation of road sections, the levels of service are as follows:

Table 9: Level of Service (LOS) criteria

Level of Service Volume / Capacity Ratio Description

A less than 0.20 free flow traffic

B 0.21 - 0.50 free flow traffic

C 0.51 - 0.70 moderate traffic

D 0.71 - 0.85 moderate / heavy traffic

E 0.86 - 1.00 heavy traffic

F greater than 1.0 forced flow, stop and go


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4. Intersections

A. At-grade Intersections

Forms of at-grade intersections:

a) 3-leg intersection: T- or Y- shaped

b) 4-leg intersection

c) Offset intersection

d) Multi-leg intersections

B. Conflicts at intersections

There are three types of conflicts among the different traffic flows present in a typicalintersection: diverging, merging and crossing. Of these three, crossing conflicts are most

critical since they may lead to more serious types of accidents. As such, it is desirable to

minimize if not eliminate these types of conflicts. Figures 8 and 9 show the typical conflicts at3- and 4-leg intersections, respectively.

Figure 8: Conflicts at a 3-leg intersection (total: 9 conflicts)


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Figure 9: Conflicts at a 4-leg intersection (total: 32 conflicts)

C. Types of Control

1) Uncontrolled Priority rules may vary by country: on a 4-way intersection traffic from the

right often has priority; on a 3-way intersection either traffic from the right haspriority again, or traffic on the continuing road. For traffic coming from the same or

opposite direction, that which goes straight has priority over that which turns off.

2) Yield yield or give way signs provide basis for priority for streets where legalsuperiority has to be established. This is often used for streets with low traffic

volumes.

3) Stop stop signs provide basis for priority for major streets over minor street approaches

with stop signs (i.e., two-way stop-controlled intersection). In cases where a four-way stop-control is employed, all approaches have equal priority. Such will work

very well for cross streets whose traffic flows are approximately equal.

4) Traffic circles it is another form of unsignalized intersection, vehicles are directed tomove around a circular path (in the case of the Philippines, counter-clockwise).Circles include roundabouts, mini-roundabouts, stop-controlled circles, signal-

controlled circles, etc. Examples are shown in Figure 10.

Roundabouts also called rotaries or rotundas, it is a form of traffic circle. The scheme

works well when the number of turning vehicles almost equals the number ofthrough vehicles. Effectiveness is dependent on traffic volume and space available

for effective weaving and geometric improvements as movement is characterized

by merging and diverging of flows. The number of conflicts present for a

roundabout provided for a 4-leg intersection is 20, including 4 crossing conflicts.


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(a) Modern Roundabout (b) Traffic circle

Figure 10: Examples of traffic circles

5) U-turn slots the scheme applied in Metro Manila is an approximation of roundabouts orrotaries. However, it usually favors a particular road (i.e., designated minor road

through traffic must negotiate U-turn slots). The number of conflicts is the same asroundabouts and a typical U-turn configuration is shown in Figure 11.

Figure 11: Typical U-turn scheme configuration


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6) Signals control of traffic is done by separation in time, i.e., conflicts at intersections are

minimized by giving right-of-way to particular movements. Critical conflicts such

as crossing and merging are practically eliminated with only a maximum of 2diverging movements allowed at any given time given the phasing of traffic flows.

Figure 12: Example of phasing at a 4-leg intersection

7) Grade separation traffic flows are separated in space. These are applied at intersections

of major roads or highways, especially in cases where traffic volume is heavy alongparticular movements. Grade separation typically involves overpasses, underpasses

or combinations. A full cloverleaf is an example of grade separation provided forall typical movements at a 4-leg intersection.

(a) EDSA-Ortigas (b) Balintawak

Figure 13: Examples of grade separation

Major considerations: Minimize conflicts Minimize delay Facilitate pedestrian movement

1

3

2

4


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D. Channelization

Objectives of channelization: Prohibition of movements Definition of vehicle paths

Promotion of safe speeds Separation of conflicts Angles of cross and merge Facilitation of high priority movements Facilitation of traffic control Accommodation of slow and decelerating vehicles Safe refuge for pedestrians

Figure 14: Examples of channelization


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5. Traffic Studies

A. Definitions

Traffic Study is the collection and analysis of measurable factual data relating to traffic and

its characteristics.

Traffic studies are made:

to provide a basis for planning and designing traffic facilities

to assist traffic operation by determining the need for traffic control devices such as signs,traffic control signals, pavement markings, etc.

to evaluate the effect of changes made for traffic by conducting before and after studies

B. Standard required data

1. Document no. - code for field sheet;2. Location - exact place or area of survey; a map is used to show what was being measured

and where observers were stationed;

3. Time - year, month, date, day of the week, time of day, duration of the survey;

4. Surveyor - identity of person, post and responsibility;

5. Weather - meteorological conditions during the survey (e.g., clear, cloudy, stormy);

6. Traffic control - traffic control measures in force (e.g., truck ban, odd-even);

7. Method - survey methodology being applied (for reference in accuracy and relevance);

8. Others - factors that may have affected data (e.g., road accidents).

C. Planning and Conduct of Traffic Studies

Planning includes:

Selection and instruction of personnel

Acquisition of equipment

Preparation of appropriate survey/field forms (this will be dependent on the purpose)

Development of schedule for data collection deployment of surveyors and equipment employment

Presurveys

Conducted to determine limits in the survey

Site visit, reconnaissance, ocular inspection

test of field forms and observation posts (including identification)

Survey Plan

Purposes of the Plan:

1. to facilitate execution of survey2. to identify constraints (e.g., manpower, materials)

3. to tailor method for requirement4. to compensate for changes in personnel


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5. to determine logistical requirements6. to program information

Parts of the Plan:

I. Name of survey

II. PurposeIII.Expected outputIV.Study area - detailed definition with map of proper scaleV. Team organizationVI. EquipmentVII. Methodology

VIII. Schedule (Man-hour requirements, conveyance schedule, fuel schedule, logistics,

projected expenses)IX.Analysis - describes how the collected data will be analyzedX. Miscellaneous - any other important elements not stated before

Note: The survey report format will be similar to the survey plan format with some additions.This will include name of survey, Purpose, Description of study area, Output (summary ofmost important findings), Actual method used and analysis of data collection, Summarized

data, and Appendices (containing raw data).

D. Traffic Data Types

Traffic data tends to fall into four broad categories:1. Physical inventory2. Population characteristics

3. Operational parameters4. Special purpose data

PHYSICAL INVENTORY DATA current details concerning the existing street and highwaynetwork

Include information such as :

1) Street and highway links - direction, number of lanes, length, width and so on2) Control devices - number and location of all signs, signals and markings3) Parking spaces - number and location of all on-street and off-street parking spaces4) Roadway conditions - number, location, and severity of all physical defects to pavement

or other roadway structures

POPULATION CHARACTERISTICSDATA describe various aspects of the population of roadusers, their vehicles, and the highways on which they travel.

Road user characteristics - include data concerning the age and sex of drivers, theamount of driving they do annually, their reaction times, their visual acuity, their

accident and violation experience, etc. These are usually acquired from secondarysources or through interview surveys.

OPERATIONAL PARAMETERS are measures that quantify the characteristics of trafficstreams in motion. These focus on three primary operational parameters (volume, speed,

density)


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Frequently conducted parametric studies

1) Volume studies consists of volume counts and are the most basic as volume is the unitused to quantify traffic demand or the amount of traffic

Traffic demand - the number of vehicles that desire to traverse a particular section ofhighway during a specified time period

Traffic volume - the number of vehicles currently traversing a highway segment

Among the data that we can derive from traffic counts are :a. Average Annual Daily Traffic (AADT) - total yearly volume divided by the number of

days in a year.b. Average Daily Traffic (ADT) - total volume during a given time period (bet. 1 to 365

days) divided by the number of days in the time period.

c. 30th Highest Annual Hourly Volume (30HV) - the hourly volume corresponding to the

30th place when all hourly volumes for a designated year are arranged from highest tolowest.

Special types of volume counts:

1. Duration Counts 4. Peak hour count2. Midblock Counts 5. Cordon Counts

3. Intersection Counts

Time of study

- Peak hour

- 12 hour count (7 A.M. - 7 P.M.; 6 A.M. - 6 P.M.)

- 16 hour count (7 A.M. - 11 P.M.)- 24 hour count (Midnight to midnight)

2) Speed studies generally focus on the speed of vehicles passing a point underuncongested conditions. These studies provide information on driver desires and their

perception of reasonable operating speed.

3) Travel time and delay studies used for:

Evaluation of congestion - source, type of delays

Before and after studies - evaluation of effectiveness of change

Assignment of traffic to networks - comparison of 2 or more routes for travel time

Economic studies - data is used for benefit-cost analysis Trend studies - analysis of level of service at different times

4) Headway and spacing studies used to evaluate intersection capacity and performance(departure headway) and for studies of the interaction among different vehicle types in thetraffic stream

SPECIAL PURPOSE DATA cannot be collected by direct observation and requires additionaldata other than inventory, population and parametric data.

Among the studies focusing on special purpose data are:

1) Accident studies - concern the following:


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Identification of locations of unusually high or unacceptable accidentexperience

Acquiring sufficient information to describe each accident

Acquiring sufficient information to relate each accident to physical,environmental, and personal conditions involved in it.

2) Parking studies - involve inventories of parking supply and a variety of countingtechniques used to estimate demand. It includes gathering of information, such as trippurposes, tolerable walking distances, parking duration, etc.

3) Pedestrian studies - similar to vehicular studies but require special techniques foreffective observation. These may require interviews and other methods to obtain trip

purpose, origin, destination, etc.

4) Origin-Destination studies - involve the determination of travel patterns and is oftenused in assessing the benefits of a roadway. It may focus on vehicle trips, passenger orperson trips, or commodity flow.

Data required when considering vehicle trips:1. Origin 5. Trip purpose

2. Destination 6. Time of travel

3. Routes taken 7. Frequency of trip4. Travel time 8. Trip cost

Data required when considering person trips:

1. Origin - original origin, boarding location(s) 6. Time of travel (start)

2. Destination - alighting point(s), final

destination

7. Frequency of trip(s)

3. Transfers - location(s), waiting time, # of

transfers

8. Modes used - (e.g., walk, tricycle,

jeepney, walk)4. Travel time - original origin to final

destination

9. Travel cost - total

5. Trip purpose

Data required when considering commodity flow:

1. Origin 4. Type of goods

2. Destination 5. Volume of commodity

3. Type of vehicle 6. Frequency of trip(s)

Survey Techniques

1. Roadside interview usually 30% to 50% of volume (20% minimum if done with trafficcount)

2. Driver postcard leave questionnaire and have it mailed back (not effective in Manilaand Cebu)

3. License plate technique get license plate number for vehicles at entry and exit points.Coverage should be established beforehand

4. Lights on - drivers are asked to turn on their lights for a particular route (good for a smallarea only)


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6. Development of Traffic Management Plan

A. Typical Objectives of a Transport and Traffic Management Plan Study

Assess the existing traffic conditions through compilation of primary and secondary

data; Design an efficient traffic circulation plan to ensure smooth, safe, and environment-

friendly vehicular and pedestrian flow;

Identify traffic management measures and alternatives appropriate to alleviatecongestion;

Develop a transportation infrastructure plan for the short, medium and long-termperiods; and

Recommend policy directions to sustain programs for the short, medium, and long-term plans.

Development of the traffic management plan will involve the compilation of available dataincluding:

Public Transport Terminals Public Transport Routes Road Network Inventory Parking Facilities Accident Incidence Environmental Characteristics

B. Typical traffic and transport surveys

Classified Traffic Volume Survey Pedestrian Volume Survey Parking Survey Travel Time and Delay Survey Transportation Facilities Survey Road Network Inventory Public Transport Terminal Survey


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7. References

Department of Public Works and Highways (2004) Road Safety Design Manual.

Gerlough, D.L. and Huber, M.J. (1975) Traffic Flow Theory: A Monograph, Transportation

Research Board Special Report 165, National Research Council, Washington, D.C.

McShane, W.R. and Roess, R.P. (1990) Traffic Engineering, Prentice Hall, EnglewoodCliffs, New Jersey.

Sigua, R.G. (2008) Fundamentals of Traffic Engineering, University of the PhilippinesPress, Quezon City.

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Intro to Traffic Engineering and Management

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