TRANSPORTATION ENGINEERINGCODE: CEB 8241

Course Purpose

Provide knowledge of planning, operate and manage the transportation systems (ie facilities and traffic) so that to have safe and economical transportation facilities.Course Objectives:At the end of the course the students should be able:

i. To explain the role of transportation systems to the society

ii. To carry out transportation planning

iii. To plan, design, and manage traffic operations

iv. To carry out cost benefit analysis in transportation industry.

Pre-requisite modules:i. Highway Engineering design

ii. Geometric design and Traffic Engineeringiii. Pavement maintenance and Evaluation

iv. Highway Engineering Materials

Assessment plan:

Assignment - 2Nos (25%)

Test 1Nos (15%)

Examination 1 (60%)

1.1 INTRODUCTIONDefinitions: Transportation Engineering - is the application of technology and scientific principles to planning functional design, operation and management of facilities for any mode of transportation in order to provide safe, rapid, comfortable, convenient, economical and environmentally compatible movements of people and goods.Transportation system is the an infrastructure/facility that serves to move people and goods by the use of vehicle

1.2 Transportation Organizations

The operation of transportation services is carried out by a variety of organizations. The following categories outline the basic purposes and functions that these organizations serve:

i. Private companies that are available for hire to transport people and goods.

ii. Regulatory agencies that monitor the behavior of transportation companies in the areas such as pricing of services and safety eg DRTLA, TCAA.iii. National agencies such as Ministry of Works and Ministry of Infrastructure developments who are responsible for carrying out legislation, planning, design, construction and maintenance of transportation facilities at national level.

iv. Local agencies that are responsible for planning, design, construction and maintenance of transportation facilities at Regional, District and local levels.v. Trade associations that represents the interests of particular transportation activity such as railways, habours or intercity buses and who serves these groups by furnishing data, information and means for discussing mutual concerns eg TABOA, MUWADA etc.

vi. Professional organizations comprised of individual who may be employed by any of the transportation organizations but have common professional bonds and benefits who shares the results of their work eg AASHTO, IET etc.

vii. Organization of transportation users who wish to influence the legislative process and furnish its members with useful travel information eg TARA Tanzania road user associations.

1.3 Authorities involved in the regulation of road transport in Tanzania

i. Ministry of communication and transportation commercial licensing, implementation of national transport policy and planning various transportation modes.ii. Ministry of works axle load control, construction and maintenance of national truck roads and bridges (TANROADS).

iii. Home affairs enforcements

iv. Finance road toll

v. Regional administration regional licensing

vi. Planning commission key transport utilities (social services, business centers etc)The planning and management responsibilities are divided between Ministries responsible for transport works, Home affairs, Regional administration and Local government & Finance

2.1 Role of transportation in society

Transportation is a non separable part of any society. It exhibits a very close relation to the style of life, the range and location of activities and the goods and services which will be available for consumption. Advances in transportation has made possible changes in the way of living and the way in which societies are organized and therefore have a great influence in the development of civilizations. Transportation is responsible for the development of civilizations from very old times by meeting travel requirement of people and transport requirement of goods. Such movement has changed the way people live and travel. In developed and developing nations, a large fraction of people travel daily for work, shopping and social reasons. But transport also consumes a lot of resources like time, fuel, materials and land.

i. Economic role of transportation

Economics involves production, distribution and consumption of goods and services. People depend upon the natural resources to satisfy the needs of life but due to difference in local resources, there is a lot of difference in standard of living in different societies. So there is an immense requirement of transport of resources from one particular society to other. These resources can range from material things to knowledge and skills like movement of doctors and technicians to the places where there is need of them.

a. The place, time, quality and utility of goods

For example if commodities are produced at one place and wanted by people of another place distant x, then the price of the commodity is dependent on the distance between two centers and the system of transportation between two points. With improved system the commodity will be made less costly at consumers place.

b. Changes in location of activities

The reduction of cost of transport does not have same effect on all locations. In case two different place supply commodities to one town. With similar condition of transport system the near place to town will supply a lot of commodities than the far one. But due to improvement of road network between the far place and the town, then the far place becomes the supply point of product/commodities.

ii. Social role of transportation

Transportation has always played an important role in influencing the formation of urban societies. Although other facilities like availability of food and water played a major role, the contribution of transportation can be seen clearly from the formation, size and pattern, and the development of societies, especially urban centers.

a. Formation of settlements

From the beginning of civilization, the man is living in settlements which existed near banks of major river junctions, a port, or an intersection of trade routes. b. Size and pattern of settlements

The initial settlements were relatively small developments but with due course of time, they grew in population and developed into big cities and major trade centers. The size of settlements is not only limited by the size of the area by which the settlement can obtain food and other necessities, but also by considerations of personal travels especially the journey to and from work. The increased speed of transport and reduction in the cost of transport has resulted in variety of spatial patterns.

c. Growth of urban centers

When the cities grow beyond normal walking distance, then transportation technology plays a role in the formation of the city. For example, many cities in the plains developed as a circular city with radial routes, where as the cities beside a river developed linearly. The development of automobiles and other factors like increase in personal income, and construction of paved road network, the settlements were transformed into urban centers of intense travel activity.

iii. Political role of transportation

The world is divided into numerous political units which are formed for mutual protection, economic advantages and development of common culture. Transportation plays an important role in the functioning of such political units.

a. Administration of an area

The government of an area must be able to send/get information to/about its people. It may include laws to be followed, security and other needful information needed to generate awareness. An efficient administration of a country largely depends on how effectively government could communicate this information to all the country. However, with the advent of communications, its importance is slightly reduced.

b. Political choices in transport

These choices may be classified as communication, military movement, and travel of persons and movement of freight. The primary function of transportation is the transfer of messages and information. It is also needed for rapid movement of troops in case of emergency and finally movement of persons and goods. The political decision of construction and maintenance of roads has resulted in the development of transportation system.

iv. Environmental role of transportation

The negative effects of transportation are more dominating than its useful aspects as far as transportation is concerned. There are numerous categories into which the environmental effects have been categorized. They are explained in the following sections.

a. Safety aspectGrowth of transportation has a very unfortunate impact on the society in terms of accidents. Worldwide death and injuries from road accidents have reached epidemic proportions. Several people killed and about 15 million injured on the road accidents annually. Increased variation in the speeds and vehicle density resulted in a high exposure to accidents. Accidents result in loss of life and permanent disability, injury, and damage to property. Accidents also cause numerous non-quantifiable impacts like loss of time, grief to the relatives of the victim, and inconvenience to the public. The loss of life and damage from natural disasters, industrial accidents, or epidemic often receive significant attention from both government and public. This is because their occurrence is concentrated but sparse. On the other hand, accidents from transport sector are widespread and occur with high frequency.

b. Air Pollution

All transport modes consume energy and the most common source of energy is from the burning of fossil fuels like coal, petrol, diesel, etc. The relation between air pollution and respiratory disease has been demonstrated by various studies and the detrimental effects on the planet earth are widely recognized recently. The combustion of the fuels releases several contaminants into the atmosphere, including carbon monoxide, hydrocarbons, oxides of nitrogen, and other particulate matter. Hydrocarbons are the result of incomplete combustion of fuels. Particulate matters are minute solid or liquid particles that are suspended in the atmosphere. They include aerosols, smoke, and dust particles. These air pollutants once emitted into the atmosphere, undergo mixing and disperse into the surroundings.

c. Noise pollution

Sound is acoustical energy released into atmosphere by vibrating or moving bodies where as noise is unwanted sound produced. Transportation is a major contributor of noise pollution, especially in urban areas. Noise is generated during both construction and operation. During construction, operation of large equipments causes considerable noise to the neighborhood. During the operation, noise is generated by the engine and exhaust systems of vehicle, aerodynamic friction, and the interaction between the vehicle and the support system (road-tire, rail-wheel). Extended exposure to excessive sound has been shown to produce physical and psychological damage. Further, because of its annoyance and disturbance, noise adds to mental stress and fatigue.

d. Energy consumption

The spectacular growth in industrial and economic growth during the past century has been closely related to an abundant supply of inexpensive energy from fossil fuels. Transportation sector is un-believed to consume more than half of the petroleum products. The compact of the shortage of fuel was experienced during major wars when strict rationing was imposed in many countries. The impact of this had cascading effects on many factors of society, especially in the price escalation of essential commodities. However, this has few positive impacts; a shift to public transport system, a search for energy efficient engines, and alternate fuels. During the time of fuel shortage, people shifted to cheaper public transport system. Policy makers and planners thereafter gave much emphasis to the public transit which consumes less energy per person. The second impact was in the development of fuel-efficient engines and devices and operational and maintenance practices. A fast depleting fossil fuel has accelerated the search for energy efficient and environment friendly alternate energy source. The research is active in the development of bio-fuels, hydrogen fuels and solar energy.

v. Other impacts

Transportation directly or indirectly affects many other areas of society and few of them are listed below:

Almost all cities use 20-30 percent of its land in transport facilities. Increased travel requirement also require additional land for transport facilities. A good transportation system takes considerable amount of land from the society.

Aesthetics of a region is also affected by transportation. Road networks in quite country side are visual intrusion. Similarly, the transportation facilities like fly-overs are again visual intrusion in urban context.

The social life and social pattern of a community is severely affected after the introduction of some transportation facilities. Construction of new transportation facilities often requires substantial relocation of residents and employment opportunities.3.1 Introduction to Transportation modes

The following are the major transport modes with their movement systems and technologies.

i. Air way international, national, regional or chartered airway, they are used by aircrafts to transport passengers and cargo. The airports are the terminals of aircrafts using the airways.

ii. Highway/main land Freeway, Arterial roads, Collectors, Feeder roads and/or Rural roads, they are used by cars, buses and trucks to carry people and goods from one place to another.iii. Rail way interstates/nations, regional and urban or and/ cities, they are used by trains to transport cargos and passenger from one place to another.iv. Marine/water ways ocean shipping, lake and river/canal, they are used by water vessels ie ships, ferries, boats etc to transport mostly cargo and people.

v. Continuous flow systems includes pipelines for transporting local gases, storm water, waste water, water supply, crude oils etc, belts and escalators used to transport people and small luggage for short distances, Cables and lifts focus for short distance for rough terrains.

3.2 Transportation Systems

The transportation systems includes transportation facilities, transportation modes, passenger, freights, administrations, organizations and private sectors on which the transportation facilities has be planned, designed & constructed, operated, managed and maintained so that the transportation modes should provide effective transportation services at the affordable costs to the market they serve.

a. Effectiveness - is described in terms of accessibility of the mode, level of mobility it provides and productivity of transport mode.i. Accessibility refers to the cost of getting to and from the mode in questionii. Mobility is described in terms of speed or travel time. A distinction is made between line haul speeds and door to door travel time.

iii. Productivity refers to some measures of the total amount of transportation provided per unit time. The amount of transportation is usually thought of as the product of the volume of goods or passengers carried and distance.

b. Costs are described in terms of capital costs and operating costs. Capital costs include right of way, construction costs, vehicles and other equipment costs, operating costs including costs of labour, fuel, spare parts and maintenance costs of facilities and equipments/vehicles.

c. Markets are described in terms of extent to which the mode in question carries passengers and freights/cargos.

d. Efficiency refers to the relationship between direct costs (capital and operating) and indirect costs eg adverse environment impacts, safety etc of the transportation and the productivity of the system.

Generally a transportation system is a combination of links and nodes together to form a transportation networks. The links are the road segments and nodes are the junction and terminals.

In order to have a good operating transportation system, both the links and nodes should operate in a better level of service (LOS) otherwise the facility or system will fail due to traffic congestion/jam.

4.1 Traffic Flow Behaviour on Road segment/link

Traffic Flow Theory is a tool that helps transportation engineers understand and express the properties of traffic flow. At any given time, there are millions of vehicles on our roadways. These vehicles interact with each other and impact the overall movement of traffic, or the traffic flow. Whether the task is evaluating the capacity of existing roadways or designing new roadways, most transportation engineering projects begin with an evaluation of the traffic flow. Therefore, the transportation engineer needs to have a firm understanding of the theories behind Traffic Flow Analysis.

4.2 Types of Traffic Flow

Traffic flow has been divided into two primary types:

1. Uninterrupted flow - is the flow regulated by vehicle to vehicle interactions and interactions between vehicles and the roadway. Occurs when vehicles traversing a length of roadway are not required to stop by any cause external to the traffic stream, such as traffic control devices. For example, vehicles traveling on an interstate highway are participating in uninterrupted flow. 2. Interrupted flow- is the flow regulated by an external means, such as a traffic signal. Under interrupted flow conditions, vehicle to vehicle interactions and vehicle to roadway interactions play a secondary role in defining the traffic flow.

4.3 Traffic Flow Parameters

Traffic flow is a difficult phenomenon to describe without the use of a common set of terms. The following paragraphs will introduce most of the common terms that are used in discussions about traffic flow.

i. Speed (v)

The speed of a vehicle is defined as the distance it travels per unit of time. Most of the time, each vehicle on the roadway will have a speed that is somewhat different from those around it. In quantifying the traffic flow, the average speed of the traffic is the significant variable. The average speed, called the space mean speed, can be found by averaging the individual speeds of all of the vehicles in the study area.ii. VolumeVolume is simply the number of vehicles that pass a given point on the roadway in a specified period of time. By counting the number of vehicles that pass a point on the roadway during an interval of 15minute period, you can arrive at the 15minute volume. Volume is commonly converted directly to flow (q), which is a more useful parameter.

iii. Flow (q)

Flow is one of the most common traffic parameters. Flow is the rate at which vehicles pass a given point on the roadway, and is normally given in terms of vehicles per hour. The 15minute volume can be converted to a flow by multiplying the volume by four.

iv. PHF (Peak Hour Factor)This describes the relationship between hourly volume and the maximum rate of flow within the hour: PHF = hourly volume/maximum rate of flow. For the 15 minute periods, PHF = volume/4 x (maximum 15 minute volume within the hour)

v. Density (k)

Density refers to the number of vehicles present on a given length of roadway. Normally, density is reported in terms of vehicles per mile or vehicles per kilometer. High densities indicate that individual vehicles are very close together, while low densities imply greater distances between vehicles.

vi. Headway (h)

Headway is a measure of the temporal space between two vehicles. Specifically, the headway is the time that elapses between the arrival of the leading vehicle and the following vehicle at the designated test point. You can measure the headway between two vehicles by starting a chronograph when the front bumper of the first vehicle crosses the selected point, and subsequently recording the time that the second vehicles front bumper crosses over the designated point. Headway is usually reported in units of seconds.

vii. Spacing (s)

Spacing is the physical distance, usually reported in feet or meters, between the front bumper of the leading vehicle and the front bumper of the following vehicle. Spacing complements headway, as it describes the same space in another way. Spacing is the product of speed and headway.

viii. Gap (g)

Gap is very similar to headway, except that it is a measure of the time that elapses between the departure of the first vehicle and the arrival of the second at the designated test point. Gap is a measure of the time between the rear bumper of the first vehicle and the front bumper of the second vehicle, where headway focuses on front-to-front times. Gap is usually reported in units of seconds.

ix. Clearance (c)

Clearance is similar to spacing, except that the clearance is the distance between the rear bumper of the leading vehicle and the front bumper of the following vehicle. The clearance is equivalent to the spacing minus the length of the leading vehicle. Clearance, like spacing, is usually reported in units of feet or meters.

x. Jam Density-- the density when speed and flow are zero.

xi. ShockwavesShockwaves occur as a result of differences in flow and density which occur when there are constrictions in traffic flow. These constrictions are called bottlenecks. The speed of growth of the ensuing queue is the shockwave, and is the difference in flow divided by the difference in density.

xii. Space Mean Speed-- the arithmetic mean of the speed of those vehicles occupying a given length of road at a given instant.

xiii. Spacing-- the distance between vehicles moving in the same lane, measured between corresponding points (front to front) of consecutive vehicles.

xiv. Speed-- the time rate of change of distance.xv. Time Mean Speed-- the arithmetic mean of the speed of vehicles passing a point during a given time interval.

xvi. Travel Time-- the total time required for a vehicle to travel from one point to another over a specified route under prevailing conditions.

4.4 Speed-Flow-Density Relationship

Speed, flow, and density are all related to each other. The relationships between speed and density are not difficult to observe in the real world.

Under uninterrupted flow conditions, speed, density, and flow are all related by the following equation:

q = k*v

Where q = Flow (vehicles/hour)v = Speed (miles/hour, kilometers/hour)k = Density (vehicles/mile, vehicles/kilometer)

Because flow is the product of speed and density, the flow is equal to zero when one or both of these terms is zero. It is also possible to deduce that the flow is maximized at some critical combination of speed and density.

Two common traffic conditions illustrate these points. The first is the modern traffic jam, where traffic densities are very high and speeds are very low. This combination produces a very low flow. The second condition occurs when traffic densities are very low and drivers can obtain free flow speed without any undue stress caused by other vehicles on the roadway. The extremely low density compensates for the high speeds, and the resulting flow is very low

4.5 Special Speed & Density Conditions

The discussion of the speed-flow-density relationship mentioned several speed-density conditions. Two of these conditions are extremely significant and have been given special names.

i. Free Flow Speed

This is the mean speed that vehicles will travel on a roadway when the density of vehicles is low. Under low-density conditions, drivers no longer worry about other vehicles. They subsequently proceed at speeds that are controlled by the performance of their vehicles, the conditions of the roadway, and the posted speed limit.

ii. Jam Density

Extremely high densities can bring traffic on a roadway to a complete stop. The density at which traffic stops is called the jam density.

4.6 Greenshields Model on Traffic Flow

Green shield developed a model of uninterrupted traffic flow that predicts and explains the trends that are observed in real traffic flows. Green shield made the assumption that, under uninterrupted flow conditions, speed and density are linearly related. This relationship is expressed mathematically and graphically (see the figure 1 below).

Basic Flow Equations:

From figure b: v = A-B*k

Where A & B are the constants determined from the field observations. This is normally done by collecting velocity and density data in the field, plotting the data, and then using linear regression to fit a line through the data points. The constant A represents the free flow speed, while A/B represents the jam density.

Inserting Greenshields speed-density relationship into the general speed-flow-density relationship yields the following equations:

q=(A-B*k)*k or q=A*kB*k2

Where:q = flow (vehicles/hour)A,B = constants k = density (vehicles/kilometer)

This new relationship between flow and density provides an avenue for finding the density at which the flow is maximized.

dq/dk = A 2*B*ksetting dq/dk = 0 yields: k = A/(2*B)

Therefore, at the density given above, the flow will be maximized. Substituting this maximized value of k into the original speed-density relationship yields the speed at which the flow is maximized.

v = A B*(A/(2*B)) or v = A/2

This indicates that the maximum flow occurs when traffic is flowing at half of free-flow speed (A). Substituting the optimum speed and density into the speed-flow-density relationship yields the maximum flow.

q = (A/2)*(A/(2*B)) or q = A2/(4*B)

As you can see, Greenshields model is quite powerful. The following can be derived from Greenshields model:

When the density is zero, the flow is zero because there are no vehicles on the roadway.

As the density increases, the flow also increases to some maximum flow conditions.

When the density reaches a maximum, generally called jam density, the flow must be zero because the vehicles tend to line up end to end (parking lot conditions).

As the density increases the flow increases to some maximum value, but a continual increase in density will cause the flow to decrease until jam density and zero flow conditions are reached.

4.7 Time-Space Diagrams

A timespace diagram is commonly used to solve a number of transportation- related problems. Typically, time is drawn on the horizontal axis and distance from a reference point on the vertical axis. The trajectories of individual vehicles in motion are portrayed in this diagram by sloping lines, and stationary vehicles are represented by horizontal lines. The slope of the line represents the speed of the vehicle. Curved portions of the trajectories represent vehicles undergoing speed changes such as deceleration.

Diagrams that show the position of individual vehicles in time and in space are very useful for understanding traffic flow. These diagrams are especially useful for discussions of shock waves and wave propagation.

The time-space diagram is a graph that describes the relationship between the location of vehicles in a traffic stream and the time as the vehicles progress along the highway. The following diagram is an example of a time-space diagram.

Time-space diagrams are created by plotting the position of each vehicle, given as a distance from a reference point, against time. The first vehicle will probably start at the origin, while the vehicles that follow wont reach the reference point until slightly later times. Reductions in speed cause the slopes of the lines to flatten, while increases in speed cause the slopes to become greater. Acceleration causes the time-space curve for the accelerating vehicle to bend until the new speed is attained. Curves that cross indicate that the vehicles both shared the same position at the same time. Unless passing is permitted, crossed curves indicate collisions

Shock Waves

Shock waves that occur in traffic flow are very similar to the waves produced by dropping stones in water. A shock wave propagates along a line of vehicles in response to changing conditions at the front of the line. Shock waves can be generated by collisions, sudden increases in speed caused by entering free flow conditions, or by a number of other means. Basically, a shock wave exists whenever the traffic conditions change.

The equation that is used to estimate the propagation velocity of shock waves is given below.

vsw = (qb qa)/(kb ka)

Wherevsw = propagation velocity of shock wave (km/hour)qb = flow prior to change in conditions (vehicles/hour)qa = flow after change in conditions (vehicles/hour)kb = traffic density prior to change in conditions (vehicles/mile)ka = traffic density after change in conditions (vehicles/mile)

Note the magnitude and direction of the shock wave.

(+) Shock wave is travelling in same direction as traffic stream.(-) Shock wave is traveling upstream or against the traffic stream.

For example, lets assume that an accident has occurred and that the flow after the accident is reduced to zero. Initially, the flow was several vehicles per hour. Also, the density is much greater after the accident. Substituting these values into the shock wave equation yields a negative (-) propagation velocity. This means that the shock wave is traveling against the traffic. If you could look down on this accident, you would see a wave front, at which vehicles began to slow from their initial speed, passing from vehicle to vehicle back up the traffic stream. The first car would notice the accident first, followed an instant later by the second car. Each vehicle begins slowing after its driver recognizes that the preceding vehicle is slowing.

4.8 Traffic Engineering Studies

The purpose of traffic engineering studies

i. Manage the physical systems eg taking inventories of facilities.

ii. Investigate trends over time eg collection of accident data and observe the impact with time for any modification or improvement.

iii. Calibrate relationships especially empirical relationships that describe traffic streams or estimate traffic parameters.

iv. Assessing the system performance eg measure speed or travel hour and check the level of service of the facility.Typical Traffic Engineering Studies

1. Volume studies quantify traffic demand, useful information for design and operation of the facility.

2. Speed Critical input for design, control and safety aspects.

3. Travel time gives indication for performance of the facility in terms of congestion level

4. Delay studies measures the amount of stopped delay along the facility.

5. Density studies can be determined by measuring volume and speed on site and calculating density.

6. Head ways and spacing can be done between individual point of vehicles

Other special studies includes

1. Accident studies2. Parking studies

3. Pedestrian studies

4. Studies of the goods movements from central business district (CBD)

5. Calibration studies.4.9 TRAFFIC FORECASTING PARAMETERS, K30 & D30

Traffic parameters (K and D) are required to convert AADT into Design Hour Volume (DHV) for a design project.

DHV = AADT X K

DDHV = AADT x KxD

ADT Average Daily Traffic counted for 24hours

AADT Average Annual Daily Traffic counted for 24hours within 365 days consecutive

AAWT Average Annual Weekly Traffic excluding the weekends (260 days)

DHV Design Hourly VolumeDDHV Directional Design Hourly Volume

K factor is the ratio of hourly traffic volume to the AADT

D factor is the ratio of total peak hour traffic travelling in the peak direction.

Capacity analysis focuses on the traffic monitored at an intersection or along a highway during a particular peak hour. The peak hour most frequently used to design roads and intersections is the 30th highest hour occurring during the design year (for rural roads K30, for urban K50). The amount of traffic occurring during this hour is called the Design Hour Volume (DHV). K30 or K50 is the ratio of the DHV to the AADT. K-factor is based on the 30th highest hour of annual traffic, it has three general characteristics:

1. The K-factor generally decreases as the AADT on a highway increases.

2. The K-factor generally decreases as development density increases.

3. The highest K-factors generally occur on recreational facilities, followed by rural, suburban, and urban facilities in descending order.

Figure 2 below shows the relation between the highest hourly volumes and AADT on arterials taken from an analysis of traffic count data covering a wide range of volumes and geographic conditions.

The curves prepared by arranging all of the hourly volumes of one year, expressed as a percentage of AADT, in a descending order of magnitude. The curves represent the following facilities: rural, suburban, urban, and the average for all locations studied. They represent a highway with average fluctuation in traffic flow. The 30th hourly peak volume is chosen because curves flatten to the right, indicating many hours in which the volume approaches 30HV. The decision to use 30HV is also based on the economics of roadway construction.

Directional Distribution

D-factors (directional distribution) are used for capacity analysis (D) and pavement design (DF). A road near the center of an urban area often has a D near 50, traffic volumes equal for both directions. A rural arterial may exhibit a significantly higher D because traffic is either traveling toward an urban area (morning) or traveling away from an urban area (evening). The D-factor used for pavement design (DF) is typically 50 percent for two-way roads or 100 percent for one-way roads.

DDHV (Peak Direction) = AADT x K30 x D30

DDHV (Opposing Direction) = AADT x K30 x (1 D30)

Using the above procedures, DDHV project traffic forecasts are generated for roadway links and intersection turning movements as needed to satisfy design requirements.

4.10 LEVEL OF SERVICE (LOS) OPERATIONAL ANALYSIS

The Level of Service (LOS) analyses are to be performed in accordance with the most current Highway Capacity Manual (HCM) procedures. The two types of highway segments are analysed to check their level of services. These are Basic Free Way segment and Two way two lane road way.a. Basic Free way SegmentThe capacity of free way segment varies from 2250 passenger car units per hour per lane (pcphpl) for free flow speed (FFS) of 90kM/hr and up to 2400pcphpl for FFS of 120km/hr or more

Generally the volume crossing the intersection is small compared to free way segment because.

Lost time at intersection results into smaller volume ie 1900veh/hr

Low speed for vehicles crossing the intersections compared to free way segment (at intersection speed=50,000veh/h

Where: LTV- left-turn flow rate in vehicle per hour; THV - opposing through movement flow rate in vehicle per hour; N - number of lanes for opposing through movement

Apart from these two criteria, there are some criteria used when protected left-turn phase is put into operation such as: speed limit, left-turn crash rate, visibility etc.

Example: The following table gives the vehicle movements at four leg intersection. The intersection layout below has the following parameters; PHF = 0.9, the v/c ratio = 0.9 and left turn vehicles shares lanes with through vehicles, number of pedestrian is moderate ( 200veh/h Yes

NB traffic: RTV = 220 > 200veh/h Yes

b. Convert the vehicle per hour volume into through car equivalent as in the table above; also take care the mixed traffic ie heavy vehicle to passenger car units.

c. Develop suitable phase system and identify critical lane volume.

d. Desirable cycle length= 65.7sec Take C = 70sec.e. Allocation of green time

The green time allocation should be proportioned to the critical lane volumes

Gef = 70 3*3 = 61 secG(A) = 61*(263/1154) = 13.9sec

G(B) = 61*(516/1154) = 27.3sec

G( C) = 61*(375/1154) = 19.8sec

f. Convert Gef into GactualGactual = Gef + Y - LtWhere: Y = y + r: y- yellow interval, r all red intervals

The following equation is generally used to determine the proper change interval

Where:

t = perception/reaction time of driver in seconds (typically taken as 1.0 second); V = approach speed in feet per second; a = deceleration rate in feet per second (typically taken as 10 feet/s2 or one third of G=9.81m/s (32.18ft/s2)); W = Width of intersection in feet; L = length of vehicle in feet (typically taken as 20 feet);

g = approach grade, percent of grade divided by 100 (add for up-grade and subtract for downgrade)

g. Check for pedestrian provisionsThe minimum green time for a phase is estimated by equation given bellow.

Where: Gp = minimum green time (s); L = crosswalk length (ft); Sp = average speed of pedestrians (ft/s); WE = effective crosswalk width (ft); 3.2 = pedestrian start-up time (s), and Nped = number of pedestrians crossing during an interval (p); 15th-percentile pedestrian speed is assumed as 4.0 ft/s (1.2m/s).

The volume to capacity ratios of critical lanes group can be determined from the following equation. This may give indication the efficient of particular lane group on each approach.

Where: Xi= ratio for lane group i; vi = actual or projected demand flow rate for lane group i (veh/h); si = saturation flow rate for lane group i (veh/h); gi = effective green time for lane group i (s), and C = cycle length (s).

Sustainable values of Xi range from 1.0 when the flow rate equals capacity to zero when the flow rate is zero. Values above 1.0 indicate an excess of demand over capacity.

5.1.2D. Compare the Cycle Length with that of using Webster Model (Delay minimization)

Critical phase Volume (Vc)Saturation flow (S)Volume to capacity ratio (v/c)

26316150.16

51616150.32

37516150.23

Sum0.71

: Set C = 65 sec.5.1.2E. Level of service of Signalized Intersection based on control delays

Delay as a measure of effectiveness based on Websters delay models

a. Uniform delay model

UD= average uniform delay per vehicle, in s/veh

It should be noted that this average delay includes the vehicles that arrive and depart on green, accruing no delay.

b. Random delay model

RD= average random delay per vehicle in s/veh

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5.2 Land Transportation Terminals Transportation terminals include buses terminals, airports, railway terminals, harbors and parking garage. Land transportation terminals may be required to perform the following functions:

i. Traffic concentration Passengers arriving from different places are grouped into batch movements, small shipments of freights are grouped into large units for more efficient handling.

ii. Processing this function includes ticketing, checking and baggage handling for passengers and preparation of way bills and other procedures for freights.

iii. Classification and sorting passengers and freights must be classified and sorted into groups according to destination and type of commodities.

iv. Loading and unloading passengers and freights must be moved from waiting rooms, loading platforms, temporary storage areas by the transportation vehicle at the origin and vice versa at the destination.v. Storage facilities for short term storage such as waiting rooms for passengers and transit sheds for freight commodities and required for assembling by concentration and classification.

vi. Traffic interchange passengers and freights arriving at a terminal often transfer to a similar or different mode of travel to complete the journey.

vii. Service availability terminals make the transportation system and its services available to the shippers and the travelling public.

viii. Maintenance and serving terminals often includes facilities for fueling, cleaning, inspection and repair of vehicles. 5.3 Essence of Terminal Planning Process

i. The objective of the terminal planners is to define the optimum design ie sufficient in size and complexity to provide suitable level of service for cheapest costs.ii. The planners must first forecast the future level of activities at the terminals such that number of passengers to be accommodated, their patterns and modes of arrival and departure and their needs while at the terminal; the volume of freights, classified by commodities type, the patterns and modes of shipments to and from the terminal.

iii. Terminal demand forecasting procedures vary depending on the terminal type and size. This can be based on historical data, empirical studies and extrapolation.

iv. In forecasting passenger terminal requirements, planners may need to perform surveys of parkers and travelers to determine current travel deficiencies and desires.v. Planners of freight terminal facilities may base on the forecasts on known or assumed relationships between tonnage of freight and the volume of sales gross regional product or other measures of economic growth.

vi. A terminal facility is usually designed to provide service for 5 to 10 years in the future.

vii. It is not advisable to design for the absolute peak day or hour demand- a typical peak hour demand is usually chosen for passengers, similar to the 30th highest hourly traffic volume recommended for highway design. A typical peak daily traffic is recommended for estimating the level of freight terminal activity.viii. Number of vehicles or passengers arriving at the terminal is not precisely predictable because of probabilistic nature of arrivals and departures. Certain aspects of terminal operation are analyzed through queuing or waiting time theory.

5.4 Queuing TheoryThis is most useful for analysis of the behavior of simple waiting lines or for studies of some components of more complex operations.

The following are the characteristics of queue theorem should be known or investigated.

i. The average rate at which units (people or vehicles or freights) arrive for service and the probability distribution of the arrival.

ii. The mean (average) service rate and the probability distribution of the services.

iii. The number of channels or servers (eg truck loading spots, toll booths, etc) and whether the channels are arranged in parallel (as in toll booth) or in series (as in vehicle repair facility).iv. The queue discipline ie the order in which arriving units be served (first come first served).

a. Assumptions of Queue theory.

i. Both, arrival and service times are random variables ie arrivals are the discrete random variables and services are continuous random variables.

ii. Service rate exceeds arrival rates

iii. No limitation on queue lengths

b. Characterization of Queue line or Waiting timeThe queuing system is said to be in a state n if there are n units (people, vehicles, etc) in a the system, including those being served. State probabilities are useful in evaluating the effectiveness of various choices of terminal design features.

The other performance measures used for the evaluation of the effectiveness of terminal design features are:

i. The number of units in the system

ii. Average length of queue

iii. The average time spent in the queue.

c. Calculations of Queue LineThe units arriving at the terminal are described by the Poisson probability distribution

Where: P(n) probability of n arrivals in a period t

mean arrival rate or volume

e Napierian logarithmic base

It may be advantageous to focus on the time interval or headways between successive arrivals rather than the number of arrival occurring during a stated interval of time. For a Poisson process it can be shown that the probability density function of interval times is:

The negative exponential distribution is commonly expressed as a cumulative distribution function expressing the probability of headway h being greater than or equal to it.

The distribution of service times is also best described by a negative exponential distribution

Where: P(st) probability that a randomly chosen services s will be equal to or greater that t

mean service timeExample 1: Queuing at the Parking Garage.

Vehicle arriving at the parking garage at an average rate of 45veh/hr are served by one attendant at an average rate of one vehicle per minute. The arrivals may be described by a poisson distribution and the service time by a negative exponential distribution.

a. What is the probability the attendant will be idle?b. If a second attendant is employed, what fraction of the time will one or both of the attendants be idle?

Soln:

a. Probability of having exactly n units in system, for attendant to be idle n = 0. = 0.25; 1veh/min = 60veh/hr.

b. The fraction of time that at least one attendant will be idle is P(0) + P(1)

= 0.45Example 2: Vehicles arrive at an entrance to a national park. There is a single gate (at which all vehicles must stop) where a ranger distributes free brochures. The park opens at 8.00am and vehicles arrive at an average flow rate of 180veh/hr. Over the entire period until dosing time, if the average time required to distribute the brochures is 15sec, describe the operational characteristics assuming Poisson distribution of the arrivals and negative exponential distribution of the service times.

Soln:

a. Average length of the queue (single channel) b. Average waiting time (of arrivals) in a queue c. Average time spent in the queue Or Average time spent = waiting time in queue + service time = 0.75 + 15/60 = 1min5.5 PARKING PLANNING AND DESIGN It is essential to provide for parking as part of road traffic system, a need for parking increases as vehicle ownerships increases.

5.5.1 Effects of Parking restraints

a. Loss of business/ trade due to lack of parking space in CBD

b. Some business owners may decide to relocate to other areas c. Spill over effects on streets causing traffic congestions and accidents.

The parking policy can be implemented for introducing price mechanism such as charge for parking, parking meter/tickets, parking permit or prohibit parking in certain areas.

5.5.2 Selecting location for Parking facilities

a. Study the activity centers ie identify activity centers that needs for parking facilities.

b. Estimate extent of generated parking demand

c. Provide parking space within the reasonable walking space (100-300m), if land is limited you can accept longer walking distance.5.5.3 On street Parking

On street parking is very significant for small streets (towns) up to 90% but for busy towns the on street parking is not effective.

Kerb parking should be considered for public transport (daradara), emergency service (fire) etc.

Center of road parking to be considered for tax and passenger cars (private cars) so as to enhance safety to people. At this location parallel parking is not recommended because of difficult in maneuvering of vehicles.

Bus stops located according to demand, but should not be very close to the intersection, at least 50m from intersection especially for signalized intersection. Also should be located at the departure side to avoid long queue or in case of many traffic turning right.

Parking duration limit for on street parking especially for CBD is 15min to 2hours.

5.5.4 Design and operation of off street Parking

There is three alternatives of off street parking ie Surface parking, multistory parking and underground parking. The choice depends on the space availability, complexity of design and construction and cost of developing and renting the facility.The problem with parking facilities is to design parking layout in order to maximize number of parking spaces obtained and facilitate vehicle circulation and access to the parking spaces. The common parking space layouts are angle parking and perpendicular parking.Recommended dimensions (ITE)

Parking angleBay widthBay widthAisle width (m)Cross area per bay (m2)

Angle Aisle (m)Perpendicular Aisle(m)

453.74.7429

6035.35.527

902.65.78.526

Australia recommendation for angle parking

Parking angleParking width (m)Aisle width (m)

302.52.8

452.53.7

602.54.6

902.55.8

Australia recommendation for minimum parking space and circulation provision for perpendicular parking

Space widthOne way aisle width (m)

2.42.5

2.52.5

2.62.5

2.72.5

5.5.5 PARKING STUDIES AND ANALYSIS

Definitions of terms

a. Space hour unit of parking that defines the use of a single space of parking for a period of one hour.

b. Parking volume number of vehicles involved in parking in a study area during a specific length of time usually 1dayc. Parking accumulation number of parked vehicles in a study area at a specific time (intervals of 1hour or 2hours and draw the cumulative curve)

d. Parking lot area under accumulation curve between two specific time

e. Parking duration length of time a vehicle is parked at a parked bay

Where: N- number of parking vehicles during time interval T(hours); s available spaces; t- parking duration limit per vehicle (hours); f- factor for parking efficiency (0.80 to 0.95)

f. Parking turn over (PTO) rate of use of parking space

5.5.6 Parking studies

The following are the studies to be conducted for parking plan and design. Collection of data on parking accumulation, parking turnover and parking duration.

Identify parking generators

Obtain information on parking demand ie make an interview with people on when they come for parking and make a records ( where do you come from, where is your destination, what is your business, arrival and departure time and his or her post card).

Inventory of existing parking spaces (ie type and number of parking, information on methods of operation-free or charged, owner of the parking)

5.5.7 Analysis of Parking data/informationSummarize the information/data and cording the information and interpreting the data for implementation (decision and design)

The information that is needed for decision and design

Number and duration of vehicles legally parked

Number and duration of vehicles illegally parked

Space hours of demand in parking

Supply of parking facilities

(i). Space hours of demand for parking D Where: D Space vehicle hours of demand for specific period of time; N Number of classes of parked duration ranges; ti mid parking duration of the ith class; ni number of vehicle parked for the ith duration range(ii). Space hours of supply S Where: S the practical number of space hours of supply for specific period of time; N - number of parking space availabe; ti total length of time in hours the ith space can be legally parked during the specified period; f efficiency factor (the average values are kerb parking=90%, garage = 80%, surface lots = 85%)Example: Consider a parking garage located in a city center (CBD) with the following surveyed data: Between 8.00am to 6.00pm, 20% of those wishing to park are turning back due to lack of space, analysis indicated that 60% of those who park are commuters with average parking duration of 9hours, 40% are shoppers with average parking duration of 2hours. Those who can not park are 20% commuters and 80% shoppers; the number of vehicles parked daily is 200. How many spaces are required to meet demand?

Solution:

a. Total arrivals: Nt = 200*100/80 = 250veh

b. Vehicles not served NL = 250 200 = 50vehc. Compute space hours of demand

Commuters served: D = 0.6*200*9 = 1080 space hours

Shoppers served: D = 0.4*200*2 = 160 space hours

Commuters not served: D = 0.2*50*9 = 90 space hours

Shoppers not served: D = 0.8*50*2 = 80 space hours

d. Total space hours of demand: D = 1080+ 160+ 90+ 80 = 1410 space hourse. Total space hours served: D = 1080 + 160 = 1240 space hours

f. Required space hours = 90+80 = 170 space hours

=170

Legal parking duration is 10hours (8am to 6pm)

S= 0.80* 10*N =170: N= 21.25

Provide 22 spaces as additional.

Home works.

1. The off street parking garage open between 7:00hours to 22:00hours. Between 8:00am to 5:00 pm 35% of those who wish to park turned off due to overflow, 50% who parked were commuters average parking duration is 8hours, 50% shoppers with average parking duration of 3hours. 100% of those who can not park are on business trip shopping. Total number of vehicles parking daily is 500, how many spaces are required to meet demand.2. Given below is the proposed parking arrangement of the multistory garage with 3 floors for parking. Up to 12% of floor space is columns and walls. The survey for parking demand indicated that 480 vehicle needs parking places for their shopping and office works, the proportion of shoppers and works is 2.6: 4.2. The works needs 3.5 times parking duration of the shoppers. The average parking duration for shoppers is 2.5hours. What area is required for parking facility?

References:

i. Khanna S.K and Justo C.E.E (1991), Highway Engineering

ii. Flaherty, Highway Engineering Vol. 1 and 2, Butler and Tanner Ltd Great Britain

iii. Robertson, Douglas H., Et. Al., Spot Speed Studies, CH.3 of Manual of Transportation Engineering Studies, Institute of Transportation Engineers, 1994, pp 33-51

iv. Highway Capacity Manual 2000.

v. Mimbela, and L., Klein, L. A Summary of Vehicle Detection and Surveillance Technologies used in Intelligent Transportation Systems. The Vehicle Detector Clearinghouse, 2000.

vi. A.S. Narasimha and Henry Mohle, Transportation Engineering Basics, 1993

vii. Tyburski, R., A review of Road Sensor Technology for Monitoring Vehicle Traffic, ITE Journal, vol. 59, no. 8, p27. Aug., 1989.

viii. Spot speed study workshop manual by Governors Highway safety Bureau Executive Office of Public safety, Boston, March 2005

Civil Engineering Department-MIST: By Duwa H.C

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