Transpo Handout 1

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.


MODES

OF

TRANSPORTATION

travel time frequency

comfort reliability

convenience safety


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 schedules and vehicles such as buses and light rail or rapid transit, that

travel designated routes with designated stops.

Paratransit. Characterized by more flexible and personalized service 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 traveling together by prearrangement. Example: shared ride taxi.


Public transportation is an important element of the total

transportation services provided within large and small metropolitan

areas. 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 the

following 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, system

innovations 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 ORGANIZATIONS

1. 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, by

furnishing 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 specialized committee 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 to information.

There are a number of factors that could affect the

performance of a driver in the highway but among them, the

following are the most prominent: AGE INFLUENCE OF ALCOHOL FATIGUE TIME OF DAY

DRIVER CHARACTERISTICS

THE HUMAN RESPONSE PROCESS

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 identification of 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 vision

o 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

HEARING PERCEPTION

The ear receives sound stimuli, which

is important to drivers only when

warning sounds, usually given out by

emergency vehicles, are to be detected.

Loss of some hearing ability is not a

serious problem, since it normally can

be corrected by a hearing aid.

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 reaction

process 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)

A driver with a perception-reaction time

of 2.5 sec is driving at 65 mi/h when she

observes that an accident has blocked the

road ahead. Determine the distance the

vehicle would move before the driver could

activate the brakes. The vehicle will

continue to move at 65 mi/h during the

perception-reaction time of 2.5 sec.

=

PROBLEM

A driver with a perception-reaction time

of 2.5 sec is driving at 75 mi/h when she

observes that an accident has blocked the

road ahead. Determine the distance the

vehicle would move before the driver could

activate the brakes. The vehicle will

continue to move at 65 mi/h during the

perception-reaction time of 2.5 sec. If

the said obstruction is 300ft away will

she have enough time for an evasive

maneuver?

PROBLEM

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

DISTANCE TRAVELED & VELOCITY ATTAINED FOR VARIABLE ACCELERATION

ACCELERATION, a = - ut The assumption of constant acceleration has some limitations,

because the accelerating capability of a vehicle at any time t is

related to the speed of the vehicle at that time, ut . The lower the speed, the higher the acceleration rate that can be attained.

Where:

= maximum acceleration rate

= constant, an inverse of time..t-1

DISTANCE TRAVELED & VELOCITY ATTAINED FOR VARIABLE ACCELERATION

ACCELERATION, constant

= 0 + 1

22

= 0 + t

SAMPLE PROBLEM

The acceleration of a vehicle is given by this equation:

ACCELERATION, a = - u0 ACCELERATION, a = 3.3 0.04uo

If the vehicle is traveling at 45mph determine its velocity after 5

sec of acceleration and the distance traveled during this time.

SOLUTION:

Distance traveled by the vehicle after the 5 sec acceleration: Convert 45mph to fps: (45mph)(5280ft/mi)(1hr/3600sec)

Convert 45mph to fps: 66 ft/sec

x =

- [ 2

(1-e- t)] +

(1 e- t)

x = 3.30.04

(5) - [ 3.30.042

(1-e- 0.04(5))] + 66

0.04(1 e- 0.04(5))

x = 337.73 ft

SAMPLE PROBLEM

The acceleration of a vehicle is given by this equation:

ACCELERATION, a = - uo ACCELERATION, a = 3.3 0.04uo

If the vehicle is traveling at 45mph determine its velocity after 5

sec of acceleration and the distance traveled during this time.

SOLUTION:

Solving the velocity of the vehicle after 5 sec of acceleration. Convert 45mph to fps: (45mph)(5280ft/mi)(1hr/3600sec)

Convert 45mph to fps: 66 ft/sec

ut =

(1-e- t) + uoe- t

ut = 3.30.04

(1-e-0.04(5)) + 66e-0.04(5)

ut = . / approx. 69 fps

Dynamic Characteristics Several 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 Resistance A 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 (2.15

2)

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 Resistance When 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 Resistance There 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 Resistance When 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 Requirements Power 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)

PROBLEM Determine the horsepower produced by a passenger car

traveling at a speed of 65 mi/h on a straight road of 5%

grade with a smooth pavement. Assume the weight of the

car is 4000 lb and the cross-sectional area of the car is 40 ft2.

P = .

= + +





SOLUTION:

Ra = 0.5 (2.15

2)

= 172.9 lb

Rr = (Crs + 2.15Crvu2)W = 72 lb

= ( ) = 200 lb

= + + = 444.9 lb





SOLUTION:

= + + = 444.9 lb

P = .

= 77.3 hp

Transpo Handout 1

Documents

Transcript of Transpo Handout 1