Download - 04 CE 122 Traffic Characteristics
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School of CE-ENSEMapua Institute of Technology (MIT)
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Human factors (Road Users) Drivers
Passengers
Pedestrians
Cyclists
Vendors
Vehicle characteristics
Traffic Flow/Roadway Environment
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Design Driverrange of drivers whose abilities and limitations should be takeninto account in designing roads, vehicles, traffic control devices,road maps and other aids to control, guidance and navigation
Perception-Reaction TimeHow quickly a driver can respond to a situationInterval between the appearance of some object or condition inthe drivers field of view and the initiation of a responsePRT= 2.5 seconds used for design standards by the AmericanAssociation of State Highway and Transportation Officials (AASHTO)1.5 seconds for perception and 1.0 seconds for making theresponse
Information Processing and Perception
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Perception-Reaction Time Process
Perception the driver sees a control device, warning sign, orobject on the road
Identification the driver identifies the object or controldevice and thus understands the stimulus
Emotion the driver decides what action to take in responseto the stimulus, ex. To step on the brake pedal
Reaction or volition the driver actually executes the actiondecided on during emotion subprocess.
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Visual Acuity ability to see fine details of an object Peripheral Vision ability of people to see objects beyond the cone of
clearest vision
Color Vision ability to differentiate one color from another.
Glare Vision and Recovery There are 2 types of glare vision: direct andspecular. Direct Glare occurs when relatively bright light appears in theindividual field of vision and specular glare occurs when the image reflectedby the relatively bright light appears in the peripheral field of vision. Both ofthem results in a decrease of visibility and cause discomfort to the eye
Depth Perception Affects the ability of a person to estimate speed anddistance. It is important on 2-lane highways during passing maneuvers,whenhead-on collision may result from lack of proper judgment of speed anddistance.
Central SightField
RightPeripheralSight Field
LeftPeripheralSight Field
V(kph) (degrees)
40 30
60 21
80 14
100 10
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length of roadway ahead that is continuously visible to thedriver
depends on the vehicle speed, vehicle size and driver PRT
minimum sight distance available should be sufficiently long
enough to enable a vehicle traveling at the design speed tostop before reaching a stationary object in its path (AASHTO)
Sight Distance
Important elements in Sight Distance
Stopping Sight Distance Decision Sight Distance
Passing Sight Distance
Intersection Sight Distance
Human Characteristics - Driver
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Time of day
Fatigue
Alcohol and drugs
AgeGender differences
Social factors
Motivation
Risk taking and risk perception
Emotions and stress
Personality
Behavioral compensation or adaptation
Other Factors Affecting the Driver
Human Characteristics - Driver
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Perception-Brake Reaction Times for Various Percentiles of Driving Population (SSD, sec)Source: Gordon et al (1984)
Percentile of DriversElements 50 75 85 90 95 100
PERCEPTION
Latency 0.24 0.27 0.31 0.33 0.35 0.45
Eye Movement 0.09 0.09 0.09 0.09 0.09 0.09
Fixation 0.20 0.20 0.20 0.20 0.20 0.20
Recognition 0.40 0.45 0.50 0.55 0.60 0.65
DECISION 0.50 0.75 0.85 0.90 0.95 1.00
BRAKE REACTION 0.85 1.11 1.24 1.42 1.63 2.16
TOTAL 2.30 2.90 3.20 3.50 3.80 3.90
Design Driver Characteristics:85thto 95thpercentile range (for safety purposes)50thpercentile value (absolute minimum value for design)
Human Characteristics - Driver
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The need to move both vehicles and pedestriansand safety at the same locations presents asignificant challenge to the traffic engineerbecause the design of roadways emphasizes
movement of motor vehicles.
Pedestrian access such as crosswalks andwalkways is often missing or inadequate in many
roads and traffic generators such as malls.
Human Characteristics - Pedestrians
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Body area (source: AASHTO)
area of the body approximated
by an ellipse
0.60 m wide and 0.50 m deep
Mean Walking Speed =
73.15 m/min. (4.4 km/hr) (AASHTO, 1984)
70.65 meters/min. (4.2 km/hr) (Filipino pedestrian)
0.50 m
0.60 m shoulder breadth
body
depth
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a.)Pedestrian Walking Speeds (PWS):Free flow = 0.6 1.8m/s (2-6fps)Mean = 1.2 1.4m/s (4-4.5fps)
= 0.9m/s (3.0fps) with large no. of elderly pedestrians(AASHTO)
Pedestrian traffic signals = 4.0fps
PWS = 143mm/minute (7.8fps) construed as runningFastest movement afoot is 10m/s (33fps)
b) Flow Rate:LOS A Free Flow = 7 or less Pedestrians/min./ftLOS E @ Capacity = 20-25 Pedestrians/min/ftLOS F Below Capacity = />25 Pedestrians/min/ft
c) Density:LOS A Free Flow = 35 ft2/PedestrianLOS E @ Capacity = 5-10 ft2/PedestrianLOS F Jam Capacity = 5 ft2 or less/Pedestrian
(@ 2 ft2/Pedestrian, nobody can move anymore)
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Condition Maximum
Tolerable
Distance(m)
Walking
Distance time
(min.)
Covered Walkway 1,500 20
Pavement with Shade 750 10
Without protectionfrom the elements
375 5
Very poor environment 180 2
* Average walking distance of Filipinos is 215 m Source: G.P. Guerilla
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Country m/min
New York, USA 81
London, England 79Israel 79
Singapore 74
Thailand 73
China 72
Metro Manila, Philippine 70.65
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1. Safety-security of the walking area guardrail/fence lighting security guard/police pedestrian signals height difference between street and sidewalk marking separation between street and sidewalk
2. Convenience-attractiveness of the walking area presence of shops
surface conditions
Width
3. Comfortability-environmental and climaticconditions presence of trees/shrubs
air quality
noise quality
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4. Continuity-walking flow of pedestrians
presence of vendors presence of street furniture
pedestrian-car conflict
5. System coherence
architectural and cohesive design of the facility to the buildings
relates to the clear orientation of the user of the facility within the area
information signs
perception of space
landmark
6. Level of congestion-space requirement and LOS of thefacility
space requirement suitable for circulation and other activities
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Important - vehicle fits the driver Static (weight & dimensions, features) & dynamic
characteristics (power, acceleration, deceleration)
Different Vehicle type i.e. car, bus, truck, etc.
DESIGN VEHICLE
Selected motor vehicle with dimensions &/or operatingcharacteristic of such a critical nature that they influenceor control the design & operation of the highway
Most important is the minimum turning radius Depending on the road classification, proportions on the
various types & sizes of vehicles expected to use thefacility
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Heavier vehicles like trucks have lower rate of acceleration thanpassenger car
Heavy vehicles at a signalized intersection will delay allpassenger cars behind it as it accelerated from a stop
Gaps will form in front of the heavy vehicle
Trucks occupy morespace: length and gap
Vehicle Characteristics
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occurs automatically when the accelerator pedal is releasedbecause of the retarding effect of the resistance to motion,including engine compression forces
for controlled deceleration, vehicle brakes are used to restrain
vehicle motion
Deceleration Performance
maximum rates are used for estimating minimum stopping
distances in emergencies
the time required to stop a vehicle is a primary considerationin almost every aspect of traffic system design and operation
Deceleration with Brakes or Braking Performance
Vehicle Characteristics
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ESIGN VEHICLE TYPE SYMBOL
Overall Overhang
Height Width Length Front Rear WB1 WB2 S T WB3
ssenger carngle-unit truckngle-unit bus
ticulated busombination trucksIntermediate semitrailerLarge semitrailerDouble Bottom
Semitrailer-full trailerInterstate Semi-Trailer
Interstate Semi-Trailer
PSUBUS
A-BUS
WB-12WB-15WB-18
WB-19*
WB-20+
1.34.14.1
3.2
4.14.14.1
4.1
4.1
2.12.62.6
2.6
2.62.62.6
2.6
2.6
5.89.1
12.1
18.3
15.216.719.9
21.0
22.5
0.91.22.1
2.6
1.20.90.6
1.2
1.2
1.51.82.4
2.9
1.80.60.9
0.9
0.9
3.46.17.6
5.5
4.06.13.0
6.1
6.1
8.29.16.1
12.8
14.3
1.2
1.2
6.1
1.6 6.4
WB1, WB2, WB3 =effective wheel basesS =distance from rear effective axle to the hitch pointT =dist. from the hitch point to the lead effective axle of the
following unit* =design vehicle with 14.6m trailer as adopted in 1982 STAA+ =design vehicle with 16.2m trailer as grandfathered in 1982 STAA
Typical Vehicle Classes and Their BasicDimensions (AASHTO, 1994), m
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Design Vehicle Type Symbol
Minimum
design
turning radius
(ft)
Minimum
inside radius
(ft)
Passenger car
Single-unit truck
Single-unit bus
Articulated bus
Semitrailer, intermediate
Semitrailer combination, large
Semitrailer-full trailer
combination
Interstate semitrailer
Interstate semitrailerTriple semitrailer
Turnpike double semitrailer
Motor home
Passenger car with travel trailer
Passenger car with boat and
trailer
Motor home and both trailer
P
SU
BUS
A-BUS
WB-40
WB-50
WB-60
WB-62a
WB-67b
WB-96WB-114
MH
P/T
P/B
MH/B
24
42
42
38
40
45
45
45
45
5060
40
24
24
50
13.8
27.8
24.4
14.0
18.9
19.2
22.2
9.1
00
20.717.0
26.0
2.0
6.5
35.0
MINIMUM TURNING RADII OF DESIGN VEHICLES (@ less than 15 kph)
Minimum Design RadiusTurning Radius -The diameter of the smallest circle in which a vehicle cancomplete a U-turn. Turning radius depends on the wheelbase of the vehicle(longer vehicles usually need more space to turn around), and maximum steering
angularity.
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AASHTO Turning Templates
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Static Characteristics
4.0 m
12 m
6.5 m 1.5 m
2.5 m
Truck
Rmin = 12 m(US =12.8m)
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Static Characteristics
2.2 m16.5 m
9.0 m 1.3 m
2.5 m
4.0m
Semi- trailer
Rmin = 12m
(US=12.2m)
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Types of Flow Uninterrupted flow
Disruptions only from other traffic in stream Interrupted flow
Disruptions from external sources (control devices, other traffic streams)
Traffic Flow ParametersMacroscopic traffic flow parameterscharacterize traffic stream as a whole
Traffic volume
Speed
Density
Microscopic traffic flow parameterscharacterize behavior of individual vehiclesin the traffic stream with respect to each other Headway
Spacing
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Traffic Volume defined as the number of vehicles that pass a point on ahighway, or a given lane or direction of a highway, during a specified timeinterval
Unit: vehicles per unit time (ex. vehicles/hour or veh/hr or vph)Common interval: day
Daily volume parametersUnit: vehicles per day or veh/day or vpdDaily volumes are not differentiated by direction or lane but are totals for the
entire facility at a specified location
Annual average daily traffic AADT) = average 24-hr traffic volume at a givenlocation over a full 365-day yearAADT = (total number of vehicles passing the site in a year)/365
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Average annual weekday traffic AAWT) = average 24-hr traffic volumeoccurring on weekdays over a full yearAAWT = (total weekday traffic volume)/260
Average daily traffic ADT) = average 24-hr traffic volume at a given locationfor some period of time less than a year
= ADT may be measured for 6 months, a season, a month, a week or as
little as 2 days
Average weekday traffic AWT) = average 24-hr traffic volume occurring onweekdays for some period of time less than 1 year, such as for a month or aseason
if AADT > AAWT and ADT > AWT, this indicates weekend traffic is heavy andfacility serves primarily for recreational traffic
- daily volumes are useful in highway planning, however, they cannot beused alone for design or operational analysis purposes
- volume varies throughout the day
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Peak-hoursingle hour of the day that has the highest hourly volumePeak-hour volume Directional volume flow directions are separated
Used as basis of highway design and many types of operational analysis
Highways must be designed to adequately serve the peak-hour traffic volume inthe peak direction of flow (both directions of the road facility)
Operational analysis imposition of control measures, safety, capacity Peak-hourly volumes are estimated from daily volume projections
DDHV = AADT K D
where DDHV = directional design hour volume (vph)
AADT = average annual daily traffic (vpd)
K = proportion of daily traffic occurring during the peak
hour, expressed as a decimalD = proportion of peak-hour traffic traveling in the peak
direction, expressed as a decimal
Hourly Volumes
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Short-term peaks of flow within the peak hour may exceed the capacity
Observed volumes are expressed as equivalent hourly rates of flow
ex. 1000 vehicles observed in 15 minutes
= 1000 vehicles/0.25 hr = 4,000 veh/hr
US Highway Capacity Manual suggested a minimum interval for traffic analysis = 15minutes
For 15-minute periods of flow (0.25 =< PHF
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-Rate of motion, in distance per unit time
-Inverse of the time taken by a vehicle to traverse a given distance
S = d 3.6 / twhere S = speed (km/h)
D= distance traversed (m)T= time to traverse distance d (sec.)In a moving traffic stream, each vehicle travels at a different speed
Therefore, a traffic stream has a distribution of individual vehiclespeeds
A typical or average speed may characterize the traffic stream
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-Travel time= total time to traverse a given highway segment;includes stopped delays
-Running time= total time during which the vehicle is in motion while
traversing a given highway segment- does not include stopped delays
-Average Travel Speed= distance of a given segment of roaddivided by average travel time on the given segment
-Average Running Speed = distance of a given segment of roaddivided by average running on the given segment
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Operating Speed = maximum safe speed at which a vehicle canbe conducted in a given traffic stream, w/o exceeding theroads design speed
Difficult to measure; it requires a test car driven through the trafficstream consistent with the definition
Since maximum speed is judgmental matter, consistentmeasurements among test car drivers are not often achieved
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Percentile Speed =speed below which the stated percent of vehicles inthe traffic stream travel
85th percentile speed= often used as the maximum speed limits
15th percentile speed= may be used as a minimum speed for the traffic
stream
50th Percentile speed= median speed = midpoint of speed distribution
Spot speed studies= to determine speeds that drivers select when notaffected by traffic congestion, studies are conducted under conditions
of free flow (light traffic)
Example: if 60 kph is the 85th-percentile speed = 85% of the vehicles in thetraffic stream travel at or below 60 kph
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