Post on 07-Sep-2018
Principles of Roads and Transport Engineering
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Principles of Roads and Transport Engineering
Definitions of Transportation
Transportation is everything involved in moving either the person or goods from the
origin to the destination.
Example of a trip
Transportation Engineering is defined as application of technology and scientific
principles to the planning, functional design, operation, and management of facilities
for all modes of transportation.
Modes of Transportation
Land (highways and railways)
Airways
Waterways
Pipe ways
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Historical Development of Transportation
The first forms of road transport were horses, oxen or even humans
carrying goods
Wheels appear to have been developed in “ancient Sumer” in
Mesopotamia around 5000 BC
First railroad opened in 1825.
The first pipelines in the United States were introduced in 1861.
The internal-combustion engine was invented in 1866
The first electric or cable car was produced in 1880
The first diesel electric locomotive (قاطرة) was introduced in 1921
The first diesel engine buses were used in 1938
The first limited-access highway in the United States (the Pennsylvania
Turn-pike) opened in 1940
The Interstate Highway system was initiated in 1950
The first commercial jet (طائرة نفاثة) appeared in 1958
Astronauts landed on the moon in 1969
Parameters to evaluate the transportation systems
Ubiquity (االنتشار) : The amount of accessibility to the system. For example
cars are more ubiquitous than other modes of transport.
Mobility: The quantity of travel that can be handled. The capacity of a
system to handle traffic and speed are two variables connected with
mobility. A freeway has high mobility, whereas a local road has low
mobility. Water transport may have comparatively low speed, but the
capacity per vehicle is high. On the other hand, a rail system could
possibly have high speed and high capacity.
Cost
Safety
Reliability
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Transportation and land use
Transportation and land use
Transportation modes choose with distance traveled
walking for short distances
car for medium distances
airplane for long distances
Transportation related problems
Fatal accidents, injuries, and property damage.
Public transportation usage is on the decline.
Transportation systems have a major impact on the environment.
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Traffic Engineering
Traffic Engineering is defined as “a branch of engineering which applies technology,
science, and human factors to the planning, design, operations and management of
roads, streets, bikeways, highways, their networks, terminals, and abutting lands”.
Or
“The 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 relationship with other modes of transportation”.
Elements of Traffic Engineering
1- Road users (drivers and pedestrians)
2- Vehicles
3- Roadway
Drivers' characteristics
1- Driving task
By keeping the vehicle at a desired speed and position with a lane, interaction
with other traffic, and reading guide signs.
2- Vision
Visual acuity
Peripheral vision
Color vision
Depth perception
Hearing perception
3- Perception-reaction time (P.I.E.V)
Perception (seeing the stimuli)
Interpretation (understanding the stimuli)
Evaluation of appropriate response (i.e., decision)
Volition or response (i.e., apply the reaction)
P.I.E.V. Refers to the time taken to detect the target, identify the target, decide
on response and initiate the response. Perception-reaction time does not
include the time to execute the decision (e.g. stop by applying a brake). The
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perception-reaction time is not fixed for all drivers and also changes for a
same driver depend on the situations.
Factors affecting perception-reaction time
Age
Fatigue
Complexity of Cues
Presence of Drugs or Alcohol
Expectation
AASHTO (American Association of State Highways and Transportations
Officials) recommendations for reaction time:
Perception and Reaction Time: 2.5 seconds
For reaction time to traffic signal, Perception and Reaction Time: 1.0
Pedestrians' characteristics
The location of pedestrians control devices are affected by drivers as well as
pedestrian characteristics (e.g. age and speed of walking). The average walking speed
was found as about 5km/hr.
Some of pedestrians control devices
Special pedestrians’ signals
Safety zones (e.g. near the schools)
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Pedestrians’ underpasses and elevated walkways.
Vehicles' characteristics
Vehicle types
In general, there are three common types of vehicles, these are:
1- Passenger cars
Passenger cars are two-axle, four-tires, generally with seating for two to six
passengers.
2- Trucks
Vehicles with at least two-axle and six tires, and have a cargo area. Trucks are used
for commercial goods transportation.
3- Buses
Buses are designed to carry passengers and have more than four tires.
Effect of vehicle type on geometric design
AASHTO recommended 20 “Design Vehicles” based on:
Height
Width
Length
Minimum and Maximum Turning Radii
Vehicle performance
Vehicle performance is defined by how well a vehicle can accelerate, decelerate,
brake and maneuver.
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Road characteristics
Factors affecting drivers’ behavior include:
Stopping sight distance
Passing sight distance
Horizontal and vertical alignments
Superelevation
Cross slope
Number of lanes
Grades
Highway classifications
Figure 1 shows an example for the highway classifications in rural area and suggests
the following types:
1- Arterial highways provide direct service between cities and larger towns (e.g.
Freeways).
2- Collector roads: serve small towns directly and connect them to the arterials.
3- Local roads: serve individual farms and other rural land uses and distribute
traffic from/to the collector roads.
Important References
Garber, N. J. and Hoel, L. A. (2009) "Traffic and Highway Engineering",
Forth Edition, Cengage learning.
Highway Capacity Manual (HCM, 2010) Transportation Research Board,
National Research Council, Washington, D.C.
A policy on Geometric Design of Highways and Streets (2004), American
Association of State Highway and Transportation Officials (AASHTO),
Washington, D.C.
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Traffic stream elements
Traffic volume
Traffic volume is the total number of vehicles that pass over a given point or section
of a lane or roadway during a given time interval. Volumes can be expressed in terms
of veh/hr, veh/min, veh/day, …etc.
Traffic composition
Three types of vehicles are considered for the purpose of traffic analysis. These are:
Passenger cars (pcu)
Trucks and Buses
Recreational vehicles (RVs)
The overall effect of traffic operation for any vehicle type can be expressed in term of
the effect of basic unit – usually passenger car unit (pcu). Therefore, the vehicles
should be converted to pcu as follows:
Example: a rural highway on a level terrain has the following traffic composition:
50% passenger cars
30% trucks
10% buses
10% recreational vehicles
Find the total volume expressed as pcu/hr if the total volume is 5000 veh/hr.
Solution:
Volume of passenger cars= 0.5*5000=2500 veh/hr
Volume of trucks =0.3*5000=1500 veh/hr
Volume of buses=0.1*5000=500 veh/hr
Volume of recreational vehicles=0.1*5000=500 veh/hr
Total volume in pcu/hr = 2500*1 + 1500*1.5 + 500*1.5 + 500*1.2
= 2500 + 2250 + 750 + 600 = 6100 pcu
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Flow rate (q)
Flow rate is the equivalent hourly rate at which vehicles pass over a given point or
section of a lane or roadway during a given time interval of less than 1 hr, usually
15 min.
Peak flow rates and hourly volumes produce the peak-hour factor (PHF), the ratio of
total hourly volume to the peak flow rate within the hour, computed by the following
Equation:
Example: traffic volume data has been collected for 15 min time intervals as shown
below. Find the total hourly volume, flow rate and peak hour factor (PHF).
Time 7:30 – 7:45 7:45 – 8:00 8:00 – 8:15 8:15 – 8:30
Volume 250 350 300 200
Solution:
Volume = 250+350+300+200 = 1100 veh
Flow rate (q) = peak volume * number of intervals per 1 hour
= 350 * 4 = 1400 veh/hr
PHF=1100/1400=0.786
Example: traffic volume data has been collected for 10 min time intervals as shown
below. Find the total hourly volume, flow rate and PHF.
Time 7:30–7:40 7:40–7:50 7:50–8:00 8:00–8:10 8:10–8:20 8:20–8:30
Volume 150 200 300 200 150 100
Solution:
Volume = 150+200+300+200+150+100= 1100 veh
Flow rate (q) = peak volume * number of intervals per 1 hour
= 300 * 6 = 1800 veh/hr
PHF=1100/1800=0.61
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Speed
Speed (u) is the distance traveled by a vehicle during a unit of time. It can be
expressed in miles per hour (mi/h), kilometers per hour (km/h), or feet per second
(ft /sec).
Types of speeds
Several different speed parameters can be applied to a traffic stream. These include
the following:
Average running speed: A traffic stream measure based on the observation of
vehicle travel times traversing a section of highway of known length. It is the length
of the segment divided by the average running time of vehicles to traverse the
segment. Running time includes only time that vehicles are in motion.
Average travel speed (Journey speed): A traffic stream measure based on travel
time observed on a known length of highway. It is the length of the segment divided
by the average travel time of vehicles traversing the segment, including all stopped
delay times. It is also a space mean speed.
Space mean speed: A statistical term denoting an average speed based on the average
travel time of vehicles to traverse a segment of roadway.
where
space mean speed (km /hr)
n number of vehicles
ti the time it takes the ith vehicle to travel across a section of highway (sec)
ui speed of the ith vehicle (km /hr)
L length of section of highway (km)
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Time mean speed (spot speed): The arithmetic average of speeds of vehicles
observed passing a point on a highway; also referred to as the average spot speed.
The individual speeds of vehicles passing a point are recorded and averaged
arithmetically.
where
t): time mean speed (km/hr)
n: number of vehicles passing a point on the highway
ui: speed of the ith vehicle (km /hr)
Free-flow speed: The average speed of vehicles on a given facility, measured under
low-volume conditions, when drivers tend to drive at their desired speed and are not
constrained by control delay.
Example: Three vehicles are recorded with speeds of 30, 40, and 50 mi/h. Find
average time mean speed and space mean speed for these three vehicles to traverse a
section of 1 mile.
Answer:
Estimation of time mean speed:
=(30+40+50)/3=40 mi/hr
Estimation of space mean speed:
The time required for vehicles to traverse the section:
T1=1/30=0.03333 hr (i.e. 2 minutes)
T2=1/40=0.025 hr (i.e. 1.5 minutes)
T3=1/50=0.02 hr (i.e. 1.2 miutes)
= 3(1)/(0.03333+0.025+0.02)=38.9 mi/hr
Example: Four vehicles are recorded with speeds of 48, 56, 72and 72 km/hr. The
time to traverse 1 mi is 2.0 min, 1.5 min, and 1.2 min, respectively. Find average time
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mean speed and space mean speed for these four vehicles to traverse a section of
91.5m.
Answer:
Estimation of time mean speed:
=(48+56+72+72)/4= 62 km/hr
Estimation of space mean speed:
The time required for vehicles to traverse the section:
T (in seconds)=
where
S is a vehicle speed in km/hr
L is the distance traveled in meters
T1=91.5/0.278*48= 6.68sec
T2=91.5/0.278*56=5.877sec
T3=91.5/0.278*72= 4.57 sec
T4=91.5/0.278*72= 4.57sec
= 4(91.5)/(6.68+5.877+4.57+4.57)=16.87 m/sec =16.87*(3600/1000)=60.73 km/hr
Density
Density (k), sometimes referred to as concentration, is the number of vehicles
traveling over a unit length of highway at an instant in time. The unit length is usually
1 km (or mile) thereby making vehicles per km (veh/km) the unit of density.
For the given example in the figure: k=3vehicles/segment length
Segment length
(km)
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Direct measurement of density in the field is difficult; therefore, density can be
computed from the average travel speed and flow rate using the following
relationship:
Where
q is the traffic flow (veh/h),
u is the average speed (space mean speed in km/h), and
k = density (veh/km).
Time Headway
Time headway (h) is the difference between the time the front of a vehicle arrives at a
point on the highway and the time the front of the next vehicle arrives at that same
point. Time headway is usually expressed in seconds.
The relationship between traffic flow and average time headway is:
Space Headway
Space headway (d) is the distance between the front of a vehicle and the front of the
following vehicle and is usually expressed in meter or feet.
Gap Headway
Gap headway is the difference in time between the time the rear of the leading vehicle
and the front of the following vehicle. Gap headway is usually expressed in seconds.
Clear spacing
Clear spacing is the difference in length between the time the rear of the leading
vehicle and the front of the following vehicle. Gap headway is usually expressed in
feet or meter.
Graph showing time headway, space headway, gap headway and clear spacing
Time headway (sec)
Space headway (m)
(sec)
Gap headway (sec)
Clear spacing (m)
Direction of traffic
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Example: Five vehicles, as shown in the figure below, are traveling at constant
speeds on section of 230m length. Assuming that all vehicles have a same length of
4m and if speeds and clear spacing between vehicles are as shown in the figure,
estimate the following:
1) Average space mean speed
2) Average time mean speed
3) Traffic density
4) Average time headway arriving a section A-A
5) Average clear spacing
Answer:
1- Space mean speed
2- Time mean speed
3- Traffic density
veh/km
4- Estimation of average time headway:
Arrival of vehicle 2 (t2)=(30+4)/(76*1000/3600)=1.61 sec
Headway of vehicle 2 (h2)=1.61
Arrival of vehicle 3 (t3) =(80+8)/(75*1000/3600)=4.224
Headway of vehicle 3 (h3)=4.224-1.61=2.614 sec
Arrival of vehicle 4 (t4)= (140+12)/(80*1000/3600)=6.84sec
Headway of vehicle 4 (h4)=6.84-4.224=2.616sec
Arrival of vehicle 5 (t5)= (175+16)/(75*1000/3600)=9.168
Headway of vehicle 5 (h5)=9.168-6.84=2.232sec
Average time headway=(1.61+2.614+2.616+2.232)/4 = 2.268sec
5- Average clear spacing=(30+50+60+35)/4=43.75m
75km/hr 80km/hr 75km/hr 76km/hr 80km/hr 30 m 50 m 60 m 35 m Traffic direction Veh 1 Veh 2 Veh 4 Veh 5 Veh 3
A
A
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Speed-Flow-Density Diagrams
The relation between flow and density, density and speed, speed and flow, are
referred to as the fundamental diagrams of traffic flow.
a. Flow-Density curve
1. When the density is zero, flow will also be zero, since there are no vehicles on
the road.
2. When the number of vehicles gradually increases the density as well as flow
increases.
3. When more and more vehicles are added, it reaches a situation where vehicles
can’t move. This is referred to as the jam density or the maximum density. At
jam density, flow will be zero because the vehicles are not moving.
4. There will be some density between zero density and jam density, when the
flow is maximum. The relationship is normally represented by a parabolic
curve as shown in the figure.
5. The slope between point O and any other point represents the space mean
speed. For example the slope of the line OD represents the space mean speed
at density equal to k1.
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Speed-density diagram
1. Speed will be maximum (free flow speed) , when the density is minimal
2. When the density is maximum (k=kjam), the speed will be zero.
3. The simplest assumption is that this variation of speed with density is linear as
shown by the solid line in the figure. It is also possible to have non-linear
relationships as shown by the dotted lines.
b. Speed-Flow diagram
1. When the flow is minimal and approximately no vehicles on a road section,
speed is maximum (i.e. free flow speed uf).
2. When the flow gradually increases, the speed will decrease.
3. When the flow becomes minimal due to highly traffic which caused jam
density (kjam), speed will be zero (u=0) since traffic cannot move.
4. There will be some speed between zero and uf, when the flow is maximum.
This speed is called (optimum speed).
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Combined diagram
The diagrams shown in the relationship between speed-flow, speed-density, and flow-
density are called the fundamental diagrams of traffic flow. These are as shown in the
following figure.
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Speed-Flow-Density relationships
Greenshield’s suggests a linier relationship between speed and density, thus:
Therefore:
(Equation 1- speed-density relationship)
By multiplying Equation (1) by k, produces:
But , therefore:
(Equation 2- flow-density relationship)
By substituting k=q/u in Equation 1, produces:
(Equation 3- flow-speed relationship)
From Equation (2), maximum flow occurs when the differentiate of dq/dk=0
To find the density at maximum flow, dq/dk =0
, thus:
(density at maximum flow)
From Equation (3), maximum flow occurs when the differentiate of dq/du=0
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To find the speed at maximum flow, dq/du =0
(speed at maximum flow)
Thus Maximum flow
Example:
A study of freeway flow at a particular site has resulted in the following speed-density
relationship as follows:
Where u in units of mi/hr and k in unit of veh/mi
For this relationship, determine: (a) the free-flow speed, (b) jam density, (c) the speed
flow relationship, (d) the flow density relationship, and (e) maximum flow (i.e.
capacity).
Answer:
The general speed-density relationship is:
The relationship in the question could be re-written as follows:
Therefore,
uf=57.5 (mi/hr)
uf/kj=0.46
kj=57.5/0.46=125 veh/mi
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Speed-Flow relationship
The general equation is:
By substituting kj=125 and uf=57.5 produce:
or:
, then by substituting k=q/u produces:
Flow-Density relationship
The general equation is:
By substituting kj=125 and uf=57.5 produce:
or:
then by multiplying by k produces:
Maximum flow (capacity)
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Example: Two sets of vehicles are timed over a kilometer section long and flows are
also recorded. In the first set, four vehicles take 53, 56, 63 and 69 seconds when the
flow is 1500 veh/hr. In the second set, four vehicles take 70, 74, 77 and 79 seconds
when the flow is 1920 veh/hr. Estimate:
1- Estimate the capacity (maximum flow) of a section.
2- Estimate average speed and density at flow rate of 800 veh/hr.
3- If the average speed of traffic is 60km/hr, state the traffic condition (i.e.
normal or congested)?
Answer:
1- Estimating the capacity (qmax) of a section
Estimation of space mean speed for set 1:
K for set 1=q/us=1500/59.75=25.1 veh/km
Estimation of space mean speed for set 2:
K for set 2=q/us=1900/48=39.6 veh/km
By using the fundamental equation of speed-density relationship:
using data set 1:
---(1)
using data set 2 :
---(2)
Eq(1)-Eq(2) produces:
, then
---(3)
Substitute eq(3) in eq(1) produces:
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, then
and
2- Average speed and density at flow rates of 800 and 2000 veh/hr.
Speed at flow of 800 veh/hr
1.234u2 - 98.72u + 800 = 0
A=1.234, B= -98.72, C=800
u=70.85 at normal flow condition and u=9.15 at congested flow condition
Density at flow of 800 veh/hr
k=q/u=800/70.85=11.29 veh/km at normal flow condition
k=q/u=800/9.15=87.43 veh/km at congested flow condition
3- Since the speed of 60km/hr is higher than the speed at maximum flow of
1974veh/hr, speed at qmax=uf/2=40km/hr, then we expect that the traffic
condition is normal based on fundamental diagram of traffic flow (speed-flow
diagram)
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Extra questions
1- 1- A traffic stream displays average vehicle headways of 2.2 s at 50 mi/h.
Compute the density and rate of flow for this traffic stream.
2- At a given location, the space mean speed is measured as 40 mi/h and the rate
of flow as 1600 pc/h/ln. What is the density at this location for the analysis
period?
3- The following counts were taken on an intersection approach during the
morning peak hour. Determine (a) the hourly volume, (b) the peak rate of flow
within the hour, and (c) the peak hour factor.
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Capacity is the maximum hourly rate of vehicles or persons that can reasonably be
expected to pass a point, or traverse a uniform section of lane or roadway, during a
specified time period under prevailing conditions.
Demand is the principal measure of the amount of traffic using a given facility.
Demand relates to vehicles arriving while volume relates to vehicles discharging. If
there is no queue, demand is equivalent to the traffic volume at a given point on the
roadway.
Level of service (LOS) مستوى الخدمة
Level of service (LOS) is a qualitative measure describing operational conditions
within a traffic stream and their perception by drivers and/or passengers.
Types of LOS
A: free flow.
B: reasonably free flow. Maneuverability within the traffic stream is slightly restricted
C: stable flow, at or near free flow. Ability to maneuver through lanes is noticeably restricted
and lane changes require more driver awareness.
D: approaching unstable flow. Speeds slightly decrease as traffic volume slightly increase.
E: unstable flow, operating at capacity. Flow becomes irregular and speed varies rapidly.
F: forced or breakdown flow (Traffic jam)
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Types of traffic volumes
Traffic volume is the total number of vehicles that pass over a given point or section
of a lane or roadway during a given time interval; volumes can be expressed in terms
of annual, daily, hourly, or sub-hourly periods. Traffic volume could be expressed as:
1- Average Annual Daily Traffic (AADT) is the average of 24-hour counts
collected every day of the year.
If the average annual daily traffic is not known, it can be estimated from average
weekday traffic (AWDT) using the following Equation:
2- Average Daily Traffic (ADT) is the average of 24-hour counts collected over
a number of days greater than one but less than a year.
3- Peak Hour Volume (PHV) is the maximum number of vehicles that pass a
point on a highway during a period of 60 consecutive minutes.
4- Vehicle Miles of Travel (VMT) is a measure of travel along a section of road.
It is the product of the traffic volume (that is, average weekday volume or
ADT) and the length of roadway in miles to which the volume is applicable.
VMTs are used mainly as a base for allocating resources for maintenance and
improvement of highways.
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Traffic volume fluctuation
Traffic volume is changing throughout the day, the weak and the year (see following
figures for traffic volume fluctuation in Iraq and the USA).
Typical traffic variation in USA
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Typical hourly and monthly traffic variation in Iraq
Design Hourly Volume (DHV)
The figure below shows the relationship between the highest hourly volume and ADT
on rural arterial. Based on the figure, it is recommended that the hourly traffic volume
that should be used in design is the 30 highest hourly volume of the year (30 HV).
The reason is that curve steepens quickly to the left on the point of 30 HV and
indicates only few hours with higher volume (i.e. it is not economical to design based
0
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on higher traffic volume). The curve flattens to the right and indicates many hours in
which the volume is not much less than the 30 HV.
The DHV is normally expressed as a percentage of ADT (K-factor which is in range
of 0.1-0.2))
Directional Distribution
During any particular hour, traffic volume may be greater in one direction than in the
other. Directional distribution is an important factor in highway capacity analysis.
This is particularly true for two-lane highways.
According to the Highway Capacity Manual (2010), the proportion of traffic in peak
direction (i.e. directional distribution, D) is about 0.60.
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Therefore, the directional design hourly volume (DDHV) is
or
Example: a level terrain two-lane highway is expected to serve ADT of 5000 veh, find
DHV and DDHV in veh and pcu if the following information is given:
K=0.1, D=0.6
Traffic composition includes 80 passenger cars and 20% trucks.
Solution:
DHV (veh)=ADT*K
= 5000* 0.1= 500 veh
DHV (pcu)= 500*0.8*1 + 500*0.2*1.5 = 550 pcu
DDHV (veh) = ADT*K*D
=5000 * 0.1 *0.6=300 veh
DDHV (pcu) =300*0.8*1 +300*0.2*1.5 = 240 +90 =330 pcu
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Example: The daily counts of the current traffic volume for a rural highway and for
both directions, for one week of May 2000, are as follows:
Day Saturday Sunday Monday Tuesday Wednesday Thursday Friday
Daily
volume 12000 12500 10500 11500 9500 9000 8500
The traffic composition is 70% passenger cars, 20% buses and 10% trucks. The
traffic is expected to be 180% from the current traffic up to May 2020. Find the
required number of lanes for the highway if the lane capacity is 1300 pc/hr/ln.
Assume k=0.15 and D=0.6
Answer:
ADT=sum of traffic/Number of days
Current ADT= (12000+12500+10500+11500+9500+9000+8500)/7
= 10500veh/day/2directions
المرور المستقبلي اليومي باالتجاهين
Future ADT=10500*1.8=18900 veh/day/2dir.
المرور التصميمي باالتجاهين
DHV=ADT* K=18900*0.15=2835 veh/hr/2dir.
المرور التصميمي باالتجاه الواحد
DDHV=DHV*D=2835*0.6=1701 veh/hr
DDHV (pcu/hr)=1701*0.7*1 +1701*(0.3)*1.5=1956 pcu/hr
No. of lanes=
= 1956/1300 = 1.5 lanes (use 2 lanes)
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Public Transport system
Public transport is a shared passenger transport service which is available for use by
the general public.
General Modes of public transport:
Public transport modes include buses, trolleybuses, trams and trains, rapid
transit and ferries.
- Buses
Buses are used to carrying numerous passengers on short journeys.
- Coaches
Coaches are used to carry passengers for longer distance transportation when
compared with buses. The vehicles (coaches) are normally equipped with more
comfortable seating, a separate luggage compartment, video and possibly also a toilet.
They have higher standards than city buses, but a limited stopping pattern.
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- Trains
Trains are wheeled vehicles specially designed to run on railways. Trains allow high
capacity on short or long distance, but require track, signalling, infrastructure
and stations to be built and maintained.
- Trams
Trams are rail borne vehicles (مركبات منقولة بالسكك الحديد) that run in city streets or
dedicated tracks ( مسارات مخصصة) . They have higher capacity than buses, but must
follow dedicated infrastructure with rails and wires either above or below the track,
limiting their flexibility ( يقلل من مرونة استخدامها) .
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- Rapid Transit
A rapid transit railway system (also called a metro or underground) operates in an
urban area with high capacity and frequency, and grade separation from other traffic.
Rapid transit systems are able to transport large amounts of people quickly over short
distances with little land use.
- Ferry
A ferry is a boat or ship, used to carry (or ferry) passengers, and sometimes their
vehicles, across a body of water. A foot-passenger ferry with many stops is sometimes
called a water bus. Ferries form a part of the public transport systems of many
waterside cities and islands, allowing direct transit between points at a capital cost
much lower than bridges or tunnels, though at a lower speed.
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- Motorcycle
Motorcycles are used in some countries as public transportation. The motorcycles
can be used singly or with a sidecar attached, the latter often referred to as
"tricycles". They can either be hired for personal trips, like a taxi, or used for
shared trips, with set routes, like a bus.
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Sight Distance on highways
Types of sight distance:
Available Sight distance (S.D)
Stopping sight distance (S.S.D)
Passing sight distance (P.S.D)
Available Sight distance (S.D): Is the length of the roadway ahead that is
visible to the driver. هي المسافة المرئية للطريق من قبل السائق
The available sight distance on a roadway should be sufficiently long to enable a
vehicle traveling at or near the design speed to stop before reaching a stationary
object.
Obstruction
يجب ان تكون كافية لتمكن السائق من التوقف حال رؤيتة جسم متوقف لالمام ( المرئية)المسافة المتوفرة
Stopping sight distance
Stopping sight distance is the sum of two distances:
(1) Reaction distance (d1): the distance traversed by the vehicle from the instant
the driver sights an object causing a stop to the instant the brakes are applied;
and
(2) Braking distance (d2): the distance needed to stop the vehicle from the instant
brake application begins.
Thus:
S.S.D=d1 + d2
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Reaction distance (d1 in meter)=0.278VT
Where:
V is the speed of a vehicle in km/hr
T is a driver’s reaction time (recommended as 2.5 sec.)
Braking distance (d2)is calculated as follows (for a level roadway):
The recommended value for the deceleration rate is 3.4m/sec2
Where :
(a) is the deceleration rate usually taken as 3.4m/sec2
G is the percent of grade divided by 100
Therefore,
Typical S.S.D with different speeds
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Example:
The clear spacing between a vehicle and an obstruction ahead is 60m. The speed of a
vehicle is 90km/hr. Check whether this distance is satisfying the requirements of
stopping distance for the following cases:
1- level roadway
2- downgrade of -3%
3- upgrade of 3%
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Passing sight distance on a two-lane highway
Passing sight distance is a distance required to enable drivers from passing slow
vehicles in a safe way.
The minimum passing sight distance for two-lane highways is determined as the sum of
the following four distances:
d1—Distance traversed during perception and reaction time and during the
initial acceleration to the point of encroachment on the left lane.
d2—Distance traveled while the passing vehicle occupies the left lane.
d3—Distance between the passing vehicle at the end of its maneuver and the
opposing vehicle.
d4—Distance traversed by an opposing vehicle for two-thirds of the time the
passing vehicle occupies the left lane, or 2/3 of d2 above.
1-Initial maneuver distance (d1): the distance d1 traveled during the initial
maneuver period is computed with the following equation:
Note: m is usually taken as 15km/hr.
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2-Distance while passing vehicle occupies left lane (d2): Passing vehicles were
found to occupy the left lane from 9.3 to 10.4 sec. The distance d2 traveled in the
left lane by the passing vehicle is computed with the following equation:
3-Clearance length (d3). The clearance length between the opposing and
passing vehicles at the end of the passing maneuvers was found to vary from 30
to 75 m
Clearance distance (d3) based on speed of a passing vehicle
Speed (km/hr) 50-65 66-80 81-95 96-110
D3 (m) 30 55 75 90
4-Distance traversed by an opposing vehicle (d4): This is usually taken as
2/3d2.
Thus
Passing sight distance (P.S.D.) = d1+d2+d3+d4
Example: A driver is traveling on a two-lane highway (with speed of 90 km/hr) is
trying to overtake a vehicle ahead (with speed of 65 km/hr). The acceleration rate of
the passing vehicle is 3.1 km/hr/sec, and the vehicle spent 2.3 sec for the initial
maneuvering to the opposing lane and 8.1 sec traveling on it. If you know that the
distance between the overtaking and the opposing vehicles before the beginning of
the overtaking process is 450 meters. Is this distance adequate to complete the
overtaking process? Assume that the required clearance length between the
opposing and passing vehicle is 75m.
Solution:
P.S.D.= d1 +d2 +d3 +d4
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d1=0.278*2.3(90-(90-65)+3.1*2.3/2)= 43.84m
d2=0.278*90*8.1=202.66m
d3=75m
d4=(2/3)*d2=(2/3)*202.66=135.1m
P.S.D. = 43.84+202.66+75+135.1=456.6m <450 this means that it is not safe to pass
the vehicle ahead.
Example: A driver is traveling on a two-lane highway (with speed of 90 km/hr) is
trying to overtake a vehicle ahead (with speed of 75 km/hr). The acceleration rate of
the passing vehicle is 3.1 km/hr/sec, and the vehicle spent 2.5 sec for the initial
maneuvering to the opposing lane and 8.0 sec traveling on it. Find the required
passing sight distance.
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Intersections
Definition:
An intersection is defined as the general area where two or more highways join or
cross, including the roadway and roadside facilities for traffic movements within the
area.
General types of intersections;
1- At grade intersections التقاطعات السطحية
2- Interchanges- Grade separated المجسرة)التقاطعات المعزولة
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Basic Principles of intersections design
Reduce the number of conflict points
Minimize severity of potential conflicts
Provide for smooth flow of traffic
Consider both vehicles and pedestrians
Avoid multiple and compound merging and diverging
Types and Examples of at grade intersections:
1- Three-leg/T intersections
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2- Four-leg Intersections
3-Multi-leg Intersections
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4- Roundabout
Channelization of at-grade intersections
Channelization is defined as the separation of conflicting traffic movements into
definite paths of travel by traffic islands or pavement markings to facilitate the safe
and orderly movements of both vehicles and pedestrians.
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Importance of channelization
Channelized T intersection
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Pavement types
Main Types of Pavements are:
1- Flexible pavement
The wearing layer (top layer) in flexible pavement consists of bituminous materials.
Typical layers of flexible pavement
2- Rigid pavement
The wearing layer (top layer) in rigid pavement usually is constructed of Portland cement
concrete
Typical layers of rigid pavement
3- Block pavement
The wearing layer (top layer) in block pavement is constructed using interlocked block
pavement.
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Cross section elements
Figure 1 Typical cross section for two-lane highway
Roadway: The portion of a highway, including shoulders, for vehicular use.
Traveled way (Carriage way): The portion of the roadway, for the movement of
vehicles, exclusive of shoulders.
Lane width عرض المسار المروري
Lane width greatly influences the safety and comfort of driving. Lane widths of 2.7-
3.6m are generally used. The 3.6m value is the preferred width since it provides
desirable clearance between large commercial vehicles. Narrow lanes force drivers to
operate their vehicles closer to each other than they would prefer.
Cross slope االنحدار العرضي
Cross slope is an important element in cross section design and used to prevent water
from staying on the pavement surfaced and penetrate through the pavement materials.
A value of 2% is usually used for highways with good pavement quality. Using cross
slopes are undesirable because of tendency of vehicles to drift toward the low edge of
the traveled way.
The range values of cross slopes based on surface type are as follows:
Surface type Cross slope (%)
High 1.5 - 2
Low 2 - 6
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Cross slope for undivided two-lane highway
Cross slope for divided highway
-Each pavement slopes one way:
a -All lanes are crowned toward outer edge
b -All lanes are crowned toward inner edge
-Each pavement slopes two way
Shoulders االكتاف الجانبية
A shoulder is a portion of the roadway adjacent to the travel way that accommodates
stopped vehicles, emergency use, and lateral support of pavement layers. In some
cases, shoulder can accommodate bicyclists.
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Main advantages for the use of a shoulder
Provide a space for vehicles to make emergency stop
Provide a space to avoid potential crashes or reduce their severity
The sense of openness created by shoulders of adequate width contributes to
driving ease and reduce stress
Sight distance is increased and therefore improve safety
Lateral clearance is provided for traffic sign
Storm water can be discharged farther from the traveled way, and seepage
adjacent to the traveled way can be minimized
Structural support for pavement structure
Space is provided for pedestrian and bicycle use.
Shoulder width
Shoulder width varies from 0.6m to 3.6m.
A vehicle stopped on the shoulder should clear the edge of travel way by at
least 0.3m and preferably by 0.6m. Therefore, the normal shoulder width of
3.0m is recommended.
For low-volume highways, the minimum shoulder width is 0.6m and a 1.8 to
2.4m shoulder width is preferred.
For high-volume highways carrying large numbers of trucks, the minimum
shoulder width is 3m and a 3.6m shoulder width is preferred.
Shoulders wider than 3m may encourage unauthorized use of the shoulder as a
travel lane.
Shoulder slope
Concrete and bituminous shoulders should be sloped from 2 to 6%
Crushed rock shoulders should be sloped from 4 to 6%
Median الجزره الوسطية
A median is the section of a divided highway that separates the lanes in opposing
directions. The width of a median is the distance between the edges of the inside
lanes, including the median shoulders. The functions of a median include:
Providing a recovery area for out-of-control vehicles
Separating opposing traffic
Providing stopping areas during emergencies
Providing storage areas for left-turning and U-turning vehicles
Providing refuge for pedestrians
Reducing the effect of headlight glare
Providing temporary lanes and cross-overs during maintenance operations
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Roadside and Median Barriers
A median barrier is defined as a longitudinal system used to prevent vehicles from
crossing the portion of a divided highway separating the traveled ways for traffic in
opposite directions. Roadside barriers, on the other hand, protect vehicles from
obstacles or slopes on the roadside. They also may be used to shield pedestrians and
property from the traffic stream.
Curbs and Gutters
Curbs are raised structures made of either Portland cement concrete or bituminous
concrete (rolled asphalt curbs) that are used mainly on urban highways to delineate
pavement edges and pedestrian walkways.
Gutters or drainage ditches are usually located on the pavement side to provide the
principal drainage facility for the highway.
Right of Way
The right of way is the total land area acquired for the construction of a highway. The
width should be sufficient to accommodate all the elements of the highway cross
section, any planned widening of the highway, and public-utility facilities that will be
installed along the highway.
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Airways Engineering:
Airways engineering is a branch of engineering science which deals with air
transportation.
Elements of Air Transportation
1) Airport is a facility where passengers connect from ground transportation to air
transportation.
2) Aircraft
3) Passengers
4) Air traffic services help in navigating aircraft while landing, taking off, flying in
the air, over-flying any country, taxing on the ground and parking.
5) Airlines: An organization that provides scheduled flights for passengers or cargo.
6) Regulations and policies: “to ensure safe and reliable trips” example: The
International Civil Aviation Organization (ICAO).
Types of Airports:
A- International:
• Has direct service to many other airports.
• Handle scheduled commercial airlines both for passengers and cargo.
• Many international airports also serve as "HUBS", or places where non-direct
flights may land and passengers switch planes.
• Typically equipped with customs and immigration facilities to handle
international flights to and from other countries.
• Such airports are usually larger, and often feature longer runways and facilities
to accommodate the large aircraft.
B-Domestic:
• A domestic airport is an airport which handles only domestic flights or flights
within the same country.
• Domestic airports don't have customs and immigration facilities and are
therefore incapable of handling flights to or from a foreign airport.
• These airports normally have short runways which are sufficient to handle
short/medium haul aircraft.
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Main elements of a typical airport
Airports are divided into landside and airside areas. Landside areas include parking
lots, public transport railway stations and access roads. Airside areas include all areas
accessible to aircraft, including runways, taxiways and ramps. Access from landside
areas to airside areas is tightly controlled at most airports. Passengers on commercial
flights access airside areas through terminals, where they can purchase tickets,
clear security check, or claim luggage and board aircraft through gates.
Runway: A runway is a rectangular area on the airport surface prepared for the
takeoff and landing of aircraft. An airport may have one runway or several runways
which are sited, oriented, and configured in a manner to provide for the safe and
efficient use of the airport under a variety of conditions.
Taxiway: A taxiway is a path for aircraft at an airport connecting runways with
ramps, hangars, terminals and other facilities. They mostly have a hard surface such
as asphalt or concrete.
Apron: The airport apron is the area of an airport where aircraft are parked, unloaded
or loaded, refueled, or boarded. Apron is typically more accessible to users than
the runway or taxiway. However, the apron is not usually open to the general public
and a license may be required to gain access.
Terminals and gates: Terminals are used by passenger to claim boarding tickets,
clear the security check and claim their luggage. Every terminal has one or more
gates where passengers can go to the aircrafts.
Ramp: The area where aircraft parks next to a terminal to load passengers and
baggage
Hangers: Hangers is the area used for maintenance of aircrafts.