chapter-3

CHAPTER 2

Transportation

Systems

And

Organizations

CHAPTER 2: Transportation Systems and Organizations

The transportation system in a developed nation is an

aggregation of vehicles, guide ways, terminal facilities and control

systems that move freight and passengers. These systems are usually

operated according to established procedures and schedules in the

air, land and on water. Every day decisions affect the existing

transportation systems.


MODESOFTRASPORTATION

travel timefrequency

comfortreliability

conveniencesafety


ADVANTAGES & COMPLEMENTARY OF MODES


Interaction of supply and demand


Relationship between transpo demand and cost


Relationship between transpo supply and cost


Freight and passenger traffic

Freight often carries goods and supplies for certain

activities of a certain community If freights are delayed

then arrival of goods are affected also.

TRANSPORTATION ENGINEERING: CHAPTER 2

PUBLIC TRANSPORTATION is a generic term used to describe any and

all family of transit services available to urban & rural areas. Thus, it is

not a single mode but a variety of traditional and innovative services,

which should complement each other to provide system wide

mobility. Modes included within the realm of public transportation are:

Mass Transit. Characterized by fixed routes , published schedulesand vehicles such as buses and light rail or rapid transit, that

travel designated routes with designated stops.

Paratransit. Characterized by more flexible and personalizedservice than conventional fixed routes, fixed schedules services,

available to the public on demand, by subscription or on a

shared ride basis

Ridesharing. Characterized by two or more persons travelingtogether by prearrangement. Example: shared ride taxi.


Public transportation is an important element of the total

transportation services provided within large and small metropolitanareas. A major advantage of public transportation is that it can

provide high capacity, energy efficient movement in densely

travelled corridors. It also serves medium and low areas by offering an

option for auto owners who do not wish to drive, and an essential

service to those without the access to an automobile-examples:students, senior citizens, single-auto families, and others who may be

economically or physically disadvantaged.

Industry involvement in public transportation is implemented

through several national organizations; collectively they can help key

areas of concern, including funding, cost-effectiveness and

productivity, public- private cooperation, coordination, community

relations, urban planning and development.

AASHTO:American Association of State Highway and Transportation Officials

FTA: Federal Transit Administration

FHWA: Federal Highway Administration.


The future of public transportation is expected to include thefollowing elements:

1. As the population increases, the need for public transportation

should increase, but mobility will not be as great as desired due to

cost of providing the service.

2. Less federal funding will be available, placing a greater burden on

state, local and private sources.

3. Increased involvement in the private sector should result in greater

management flexibility as well as cost containment.

Though little in the way of new technology is expected, systeminnovations are likely. Increased involvement in public transportation

at all levels should result in more effective support from state and local

governments.


INTERCITY BUS TRANSPORTATION

In spite of its positive characteristics of safety and high energy-

efficiency, bus travel is generally viewed unfavorable by the

commuters. Buses are slower and less convenient than other modes of

transportation and often terminate in downtown stations that are

located in the less attractive parts of the city. Other factors such as

thorough ticketing , comfortable seats, and system wide information,

which the riding public is accustomed to receiving when travelling by

air, reinforce all negative image of intercity bus transportation.


TRANSPORTATION ORGANIZATIONS1. Private companies that are for hire to transport people and goods

2. Regulatory agencies that monitor the behavior of transportation

companies in areas such as pricing of services and safety.

3. Local agencies and authorities that are responsible for the

planning, design, construction and maintenance of transportation

facilities such as roads and airports.

4. Trade associations which represents interests of a particular

transportation activity, such as railroads or intercity buses, and

which serve these groups by furnishing data and information, byfurnishing a means for discussing mutual concerns.

5. Professional organizations composed of individuals who may be

employed by any of the transportation organizations but who

have a common professional bond and benefit from meeting with

colleagues at national conventions or in specialized committees

to share the results of their work, learn about the experiences of

others, and advance the profession through specializedcommittee activities.

6. Organizations of transportation users who wish to influence the

legislative process and furnish its members with useful information.


PRIVATE TRANSPORTATION COMPANIES

Transportation by water, air, railway, highway, or pipeline is

furnished either privately or for hire basis. Private transportation, such

as automobiles or company-owned trucks must conform only to

safety and traffic regulations.

For-Hire Transportation Companies are classified as:

1. Common Carriers : available to any user

2. Contract Carriers : available by contract to particular

market segments

3. Exempt : for hire carriers that are exempt from regulation

CHAPTER 3

Characteristics of the Driver, the Pedestrian, the Vehicle and the Road

The highway & traffic engineer must understand

not only the basic characteristics of the driver, the

pedestrian, the vehicle and the roadway but how

each interacts with each other. Information obtained

through traffic engineering studies serves to identify

relevant characteristics & define related problems.

Traffic flow is of fundamental importance developing

and designing strategies for intersection control, rural

highways, and freeway segments.

The four main components of the highway mode of

transportation are the following:

1. DRIVER

2. PEDESTRIAN

3. VEHICLE

4. ROADWAY

To provide efficient and safe transportation a knowledge of

the characteristics and the limitations of each of these four

components is essential. Their characteristics are also of primary

importance when traffic measuring devices are to be used in the

highway mode.

One problem that faces traffic and transportation engineers

when they consider driver characteristics in the design is the varying

skills and perceptual abilities. This is demonstrated by the wide range

of peoples skills or abilities to hear, see, evaluate and react toinformation.

There are a number of factors that could affect the

performance of a driver in the highway but among them, thefollowing are the most prominent:

AGE INFLUENCE OF ALCOHOL FATIGUE TIME OF DAY

DRIVER CHARACTERISTICS

THE HUMAN RESPONSE PROCESS

VISUAL RECEPTION

Receipt of stimuli by the eye (driver & pedestrian) Knowledge of human vision will therefore aid in solving several

problems in traffic engineering

Principal characteristics of the eye include: VISUAL ACUITY PERIPHERAL VISION COLOR VISION GLARE VISION GLARE RECOVERY

DRIVER CHARACTERISTICS

Ability to see fine details of an object

Classified into 2 types: (these types are important in traffic and

highway emergencies) Static Visual Acuity. The drivers ability to identify an object

when both the object and the driver are stationary. Factors that

affect Static Visual Acuity are:o Background brightness

o Contrast

o Time

Static Visual Acuity increases with an increase in illumination

up to a background brightness of about 3 candles per sq. ft.

and then remains constant even with an increase in

illumination. When other visual factors are held constant at an

acceptable level, the optimal time required for identificationof a stationary object is between 0.5 - 1.0 sec.

Visual Acuity

Ability to see fine details of an object

Classified into 2 types: (these types are important in traffic and

highway emergencies) Dynamic Visual Acuity.

o Ability to clearly detect relatively moving objects, not

necessarily in his/her direct line of visiono Most people have a clear vision within a conical range of

3 to 5

o Fairly clear vision of within a conical range of 10 to 12.

o Vision beyond this range is blurred.

Visual Acuity

Ability to see beyond the cones of clearest vision. Cone for peripheral vision could be one subtending to 160 which is

greatly affected by the speed of the vehicle.

Age affects peripheral vision.

Peripheral Vision

Ability to differentiate one color from another. Combinations of black, white and yellow have been shown to be

those to which the eyes is most sensitive.

Color Vision

ability of a person to estimate speed and distance. to compensate transportation authorities standardize the size,

shapes, and color of traffic and road signs

this ability varies from one individual to another

Depth Perception

HEARINGPERCEPTION

P E D E S T R I A N C H A R A C T E R I S T I C S

o VISUAL CHARACTERISTICS

o HEARING CHARACTERISTICS

o WALKING CHARACTERISTICS

walking speeds vary roughly from 3 - 8 ft/s

significant differences have also been observed between male

and female walking speeds

at intersections, the average walking speed of males is 4.93 ft/s

and 4.63 ft/s for females.

however, for design purposes a conservative value is necessary,

the MUTCD (Manual on uniform Traffic Control Devices)

suggests the use of 4.0 ft/s for design

disabilities are also considered in the design of pedestrian

control devices.

perception reactionprocess

the process through which

a driver or pedestrian

evaluates and reacts to a

stimulus.

commonly known as PIEV time

PERCEPTION-REACTION PROCESS

1. PERCEPTION. the driver sees a control device, warning sign or

object on the road

2. IDENTIFICATION. the driver identifies the object or stimulus

3. EMOTION. the driver identifies what action to take in response of

the stimulus

4. REACTION or VOLITION. the driver executes the action decided

(sometimes during the emotion process)

vehicle

criteria for geometric design of

highways are partly based on

vehicle characteristics

characteristics

VEHICLE CHARACTERISTICS

o STATIC CHARACTERISTICS

weight and size of the vehicle

o KINEMATIC CHARACTERISTICS

motion of the vehicle (speed and acceleration)

o DYNAMIC CHARACTERISTICS

Dynamic CharacteristicsSeveral forces act on a vehicle while it is in motion: air

resistance, grade resistance, rolling resistance, curve

resistance, and friction resistance. The extents to

which these forces affect the operation of the vehicle

are discussed in this section.

Air ResistanceA vehicle in motion has to overcome the resistance of

the air in front of it as well as the force due to the

frictional action of the air around it. The force required

to overcome these is known as the air resistance and

is related to the cross sectional area of the vehicle in

a direction perpendicular to the direction of motion

and to the speed of the vehicle.

Air Resistance

Ra = 0.5(2.152)

Where:

Ra = air resistance force (lb)

p = density of air (0.00238 lb/ft3) at sea level; less at higher

elevation

CD = aerodynamic drag coefficient (current average value for

passenger cars is 0.4; for trucks this value ranges from 0.5 to 0.8,

but a typical value is 0.5

A = frontal cross sectional area, (ft2)

u = vehicle speed, (mph)

g = acceleration of gravity (32.2 ft/sec2)

Grade ResistanceWhen a vehicle moves up a grade, component of

the weight of the vehicle acts downward, along the

plane of the highway. This creates a force acting on

the direction opposite that of the motion. This force is

the grade resistance. A vehicle traveling up a grade

will therefore tend to lose speed unless accelerating

force is applied. The speed achieved at any point

along the grade of a given rate of acceleration will

depend on the grade percentage.

Rolling ResistanceThere are forces within the vehicle itself that offer

resistance to motion. These forces are due mainly to

frictional effect on moving parts of the vehicle, but

they also include the frictional slip between the

pavement surface and the tires. The sum effect of

these forces on motion is known as rolling resistance.

The rolling resistance depends on the speed of the

vehicle and the type of pavement. Rolling forces are

relatively lower on smooth pavements than on rough

pavements.

Rolling Resistance

Rr = (Crs + 2.15Crvu2)W

Where:

Rr = rolling resistance force (lb)

Crs = constant (typically 0.012 for passenger cars)

Crv = constant (0.65x10-6 sec2/ft2 for passenger cars)


W = gross vehicle weight (lb)

FOR PASSENGER CARS

Rolling Resistance

Rr = (Ca + 1.47Cbu)W

Where:

Rr = rolling resistance force (lb)

Ca = constant (typically 0.2445 for trucks)

Cb = constant (0.00044 sec/ft for trucks)



FOR TRUCKS

The surface condition of the pavement has a

significant effect on the rolling resistance.

Curve ResistanceWhen a vehicle is maneuvered to take a curve,

external forces act on the front wheels of the vehicle.

These forces have components that have a retarding

effect on the forward motion of the vehicle. The sum

effect of these components constitutes the curve

resistance. This resistance depends on the radius of

the curve, the gross weight of the vehicle, and the

velocity at which the vehicle is moving.

Curve Resistance

Where:

Rc = curve resistance force (lb)



g = acceleration of gravity ( 32.2 ft/sec2)

R = Radius of curvature, (ft)

Rc = 0.5(2.152)

Power RequirementsPower is the rate at which work is done. It is usually

expressed in horsepower where 1HP = 550 lb-ft/sec. The

performance capability of a vehicle is measured in terms of

the horsepower the engine can produce to overcome air,

grade, curve and friction forces and put the vehicle in

motion.

P =.

Where:

P = horsepower delivered, HP


R = sum of resistance to motion, pounds (lb)

The time traveled by a vehicle between the time the

driver observes an object in the vehicles path & the timethe vehicle actually comes to a stop is longer than the

braking distance, since it includes the distance traveled

during perception-reaction time. This distance referred tois the Stopping distance S

S =1.47ut -2

30()

SAMPLE PROBLEM 2A student trying to test the braking ability of his car,

determined that he needed 32ft more to stop his car

when driving downhill on a particular road than when

driving uphill at 55mph. Assuming the coefficient of friction

between the tires and the pavement is 0.30, determine

the braking distance downhill and the percentage grade

of the highway at that section of the road.

SAMPLE PROBLEM 3A motorists traveling at 55mph on an expressway intends

to leave the expressway using an exit ramp with an

allowable speed of 30mph. At what point on the

expressway should the motorist step on her brakes in

order to reduce her speed to the maximum allowable on

the ramp just before entering the ramp? Assume that the

coefficient of friction between the tires & the pavement is

0.3 and that the alignment of this section of the road is

horizontal.

SAMPLE PROBLEM 4A motorists traveling at 55mph down a grade of 5% on a

highway observes an accident ahead of him. If the

motorist was able to stop his vehicle 30ft from the

accident site, what was the distance from the accident

when he saw the accident. Assume perception-reactiontime to be 2.5 sec and f=0.3.

Estimating VelocitiesIt is sometimes necessary to estimate the speed of a

vehicle just before it is involved in an accident. This may

be done by using the braking distance equations if skid

marks can be seen on the pavement.

1. Measure the length of the skid marks for each tire and

determine the average. This value is assumed to be the

braking distance of the vehicle.2. Determine the coefficient of friction fk by performing

trial runs at the site under similar conditions. This involves

using almost identical vehicles at known speeds uk and

measuring the distance traveled Dk3. Find the velocity uu using the obtained coefficient of

friction in step 2

Estimating Velocities

fk =

2

30

However if the speed of the vehicle upon impact is known

it can simply be expressed as:

uu = (

2+12)^1/2

SAMPLE PROBLEM 5In an attempt to estimate the speed of the vehicle just

before it hits a traffic signal pole, a traffic engineer

measured the length of the skid marks made by the

vehicle and performed trial runs at the site to obtain an

estimate of the coefficient of friction.

Length of skids: 585ft, 590ft, 580ft and 595ft

Speed of trial run by traffic engineer: 30mph

Distance traveled during trial runs: 300ft

Speed of the vehicle on impact is found at 45mph

Turning RadiiWhen a vehicle is moving around a circular curve, two

main forces in the radii direction are on it; an OUTWARD

RADIAL FORCE (centrifugal) and an INWARD RADIAL

FORCE. The inward force is due to the friction between the

tires and the roadway.

Turning Radii

Centrifugal ForceWhere:

ac = acceleration due to

curvilinear motion

ac = u2

R

u = speed of the vehicle

R = radius of the curve

W = weight of the vehicle

g = acceleration of gravity

Fc =

c

Centrifugal ForceSAMPLE PROBLEMA 1000lb car traveling at 55mph approaches a curved portion of the

highway. Determine centrifugal force that the car will experience if the

radius of the curve is 210ft.

Fc =

c

ac =

2

Fc =2

Fc =1000 [(80.67)(0.911)]2

(210)(32.2)

Fc = 371.594 lbs.

Minimum Radius of a Highway CurveAn existing horizontal curve on a highway has a radius of 268 ft. which

restricts the speed on this section of the road to only 60% of the design

speed of the highway. If the curve is to be improved so that its

maximum speed will be the design speed of the highway, determine the

minimum radius of the new curve. Assume that the coefficient of side

friction is 0.15 for the existing curve and that the rate of super elevation

is 0.08 for both the existing curve and the new curve to be designed.

SOLUTION:

R = 2

(+); 268 =

2

32.2(0.08+0.15); = 44.551 fps

Solve the maximum permissible speed on the existing curve.

= 30.307mph Determine the design speed of the highway.

let x be the DSHighway60%DSHighway =30.307 mph

DSHighway = 50.512 mph

R = 2

(+)= (50.5121.47)2

32.2(0.08+0.14)=744.458 ft

chapter-3

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