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Traffic Engineering
Topic: Traffic Studies & Data Collection
Henry Liu
CE 4211/5211 – Traffic Engineering
University of Minnesota
email: [email protected]
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Shockwaves signalized intersections
k0
q
t
x
A
C
DA
B
A
D C
B
B
A
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Traffic Studies
A traffic engineer‟s laboratory is the
surrounding roadway system
This system must be continually
monitored, evaluated, and managed
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Guiding Principles
“If you cannot tell the system performance yesterday, you cannot hope to manage your system today.”
-- Data Collection/Analysis
“Data are too valuable to only use once.”
-- Data Archive
-- Real Time and Historical
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Reasons for Traffic Studies Inventories
-- Street or highway links
-- Intersections
Operational Parameters
-- Volume studies
-- Speed Studies
-- Travel-time studies
-- Delay Studies
-- headway and spacing studies
Special purpose studies
-- Accident Studies
-- parking studies
-- Pedestrian studies
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Traffic Studies
Traffic demand/patterns will change over time,
monitoring of system will enable necessary
system changes to be identified
The effects of system “improvements” must be
justified, e.g.,
Signal timing changes
Lane additions or reconfigurations
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Traffic Studies
Data collection is the key foundation
What kind of data?
How much data?
How to collect it?
The study characteristics must be considered in answering these questions, e.g.,
Short-term or long-term study
Statistical confidence level
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Basic Measurement
Basic measurement is traffic counts (e.g., vehicles or people). Convert traffic counts into volume (or flow), demand, and capacity
Flow Rate (Volume): actual number of vehicles traversing the segment per unit time
Demand: number of vehicles that desire to traverse the segment per unit time
Capacity: maximum number that can pass through the segment per unit time
See board
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Temporal Variation
Monthly (Jan. – Dec.)
Daily (Sun. – Mon.)
Hourly (12:00 AM – 11:59 PM)
K values (e.g., K100, K30)
The ratio of the Xth highest traffic volume hour of the year to
the AADT
Historically, 30th has been used in rural planning, design and
operations. (generally flatten out from this point)
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Graphic Summary of Vehicle
Movements
2331
162 1381926
2226
126 3692075
182
296
375 853
2570
184
109
331624
663
838
2441
Total Entering Intersection
E / W
N / S
Total
1501
4772
6273
Ma
in S
tree
t
Center Street
N
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Traffic Counts Displayed in a Network
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Expanding Short Counts (Table 6-1)
Actual Counts Expanded by time Estimated Counts (veh) Estimated Flow Rates (vphpl)
Time Lane 1 Lane 2 Lane 1 Lane 2 Lane 1 Lane 2 Lane 1 Lane 2
1 5:00 PM 24 - 30.0 - 30.0 43.1 360.0 517.5
2 5:05 - 36 - 45.0 32.5 45.0 390.0 540.0
3 5:10 28 - 35.0 - 35.0 46.9 420.0 562.5
4 5:15 - 39 - 48.8 36.3 48.8 435.0 585.0
5 5:20 30 - 37.5 - 37.5 53.8 450.0 645.0
6 5:25 - 47 - 58.8 41.3 58.8 495.0 705.0
7 5:30 36 - 45.0 - 45.0 60.6 540.0 727.5
8 5:35 - 50 - 62.5 43.8 62.5 525.0 750.0
9 5:40 34 - 42.5 - 42.5 61.3 510.0 735.0
10 5:45 - 48 - 60.0 46.3 60.0 555.0 720.0
11 5:50 40 - 50.0 - 50.0 58.8 600.0 705.0
12 5:55 - 46 - 57.5 53.8 57.5 645.0 690.0
sum 192 266 240.0 332.5 493.8 656.9
fraction 0.419 0.581 0.419 0.581
Expand to 5-min
=(5/4)*24 Interpolation
=(30+35)/2
Interpolation
=(45+48.8)/2
Extrapolation
=45-(46.9-45)
=12*57.54-min counts
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Types of Traffic Volume
Average Annual Daily Traffic (AADT)
Average Annual Weekday Traffic (AAWT)
Average Daily Traffic (ADT)
Peak Hour Volumes (PHV)
Vehicle Classification (VC)
Vehicle Miles Travel (VMT)
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Peak Hour Volume (PHV)
The max # veh passing a point on a highway over 60 consecutive minutes
Peak Hour Factor (PHF)
= PHV
4 x highest 15min volume
(0.25<PHF<1)
Mainly used for urban:
Highway design (e.g., highway classification, # of lanes, signalization, etc.)
Traffic management (e.g., capacity analysis, parking, etc.)
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Vehicle Classification (VC)
Volume with respect to vehicle type
Passenger cars
2 axle trucks
3 axle trucks
Public service vehicle (PSV)
Emergency vehicle
2 wheel vehicles
Applications
Geometric design (e.g., turning radii, max. grade, lane width)
Capacity Analysis (e.g., PCU conversions)
Automated counts
Pavement & Structure design
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Vehicle Mile Travel (VMT)
ADT x roadway length
Applications:
Economic evaluation
Resource allocation (maintenance &
improvement)
Planning
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Small Network Volume Study
Amount and spatial pattern of traffic flow over a small network (e.g., CBD, airports, stadiums, etc.)
Provide valuable information for traffic planning and control (e.g., parking requirements, special events, etc.)
Control counts
Monitor volume variation patterns in the network
Counts are taken for the entire period
Coverage counts
Locations of coverage counts
Counts are taken for some periods
See board
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Example (Table 6-3)(a) Data from a on-day study
Control Station A Coverage Time of Observed
Time (pm) Count (vph) Station Count (vph) Count (vph)
12-1 825 1 12-1 840
1-2 811 2 1-2 625
2-3 912 3 2-3 600
3-4 975 4 4-5 390
4-5 1056 5 5-6 1215
5-6 1153 6 6-7 1440
6-7 938
7-8 397
(b) Computation of hourly volume proportions from control-count data
Time Count Proportion of 8-hour total
12-1 825 0.117
1-2 811 0.115
2-3 912 0.129
3-4 975 0.138
4-5 1046 0.148
5-6 1153 0.163
6-7 938 0.133
7-8 397 0.056
Total 7057 1
=825/7057
Largest value
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Example (Table 6-3)
© Expansion of hourly counts
Location Time Count 8-hr Vol (est) Peak-hr Vol (est)
1 12-1 840 7185 1174
2 1-2 625 5439 889
3 2-3 600 4643 759
4 4-5 390 2631 430
5 5-6 1215 7436 1215
6 6-7 1440 10834 1770
=840/0.117 (from (b)) =7185x0.163(from (b))
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Flow Measurement Techniques
Manual count board
Laptop & software program
Handheld electronic device
Pneumatic tubes
Inductance loop detectors
Video Imaging Analysis
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Manual Count Board
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JAMAR Handheld Devices
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Software Program
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Pneumatic Road Tubes
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Inductance Loops
Bike LoopsVehicle Loops
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Inductance Loop Signatures (1)
Sport Car
Truck
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Inductance Loop Signatures (2)
Pickup Truck
Trash Truck
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Inductance Loop Signatures (3)
Tailgating
vehicles
Vehicle with
a boat
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Video Imaging
Video camera
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Video Imaging
Autoscope hardware
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Video Imaging
Autoscope software
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Speed Data Collection
Radar gun
Inductance loop detectors
Single loop
Double loop
Video imaging
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Radar Guns
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Density
Density is performance measure upon which multilane
uninterrupted flow facility (i.e., freeways, highways)
level of service is based
Problem with density is that it is difficult to measure directly
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Density
Aerial photographs
Volume / Speed
Surrogate measure from inductance loop detectors
Ratio of occupied time to total observation time, expressed as a percent, is termed „lane occupancy‟, denoted by (phi)
To use lane occupancy for estimation of density, we must know vehicle length, then density can be estimated by
100*n timeobservatio total
timeoccupied total
eL
k5280
*100
Le is the effective vehicle length
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Travel Time
Travel time is a popular performance measure,
for several reasons
Can compare across different modes (e.g., bus,
train, car)
Easy to work with mathematically/statistically
Easy to understand by traveling public
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Travel Time Measurement Techniques
Floating Car
License plate matching
Automatic Vehicle Location (AVL)
Global Positioning Systems (GPS)
Cellular Phones
Automatic Vehicle Identification (AVI)
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Floating Car
Driving a vehicle in the traffic stream, trying
to maintain an “average” position in the
traffic stream, i.e., passing only as many
vehicles as pass you
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License Plate Matching
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Global Positioning System (GPS)
• GPS Time
• Latitude and Longitude
• Speed
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Typical GPS Data
Time
(UTC)
Latitude
(°)
Longitude
(°)
Speed
(mph)
16:27:39 30.389885 -91.242426 40.0
16:27:40 30.390090 -91.242276 40.6
16:27:41 30.390159 -91.242225 40.7
16:27:42 30.390298 -91.242122 41.0
16:27:43 30.390507 -91.241966 41.8
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Automatic Vehicle Identification
In car electronic tag, roadside reader
E.g., Electronic toll collection
•AVI tag signal types
–RF: Radio Frequency (Most common, accurate)
•900 -928 MHz (currently used in the US)
•2.45 GHz
•5.8 GHz
–IR: Infrared
•850 nm range
–Laser
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Electronic Toll Collection
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Origin-Destination (O-D) Studies
Determining the percentage of all traffic traveling from each origin point of interest to each destination point of interest
<<
< >
internal-internal cordon line (boundary of
study area)
external-internal
external trips (Oi outside)
through trips (Oi and
Dj outside)
external-externalcordon stations [1-8]
(external zones)
external trips
(Dj outside)
internal-external
1
2 3
4
56
7 8
Study AreaZ1
Z2
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O-D Measurement Techniques
Roadside Interview
Postcards
License Plate Matching
Vehicle Re-Identification Technology
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Vehicle Re-Identification Technology
Alton
ICD
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Sensor Types, Data, and Example
Sensors
Sensor
Type
Point Data: Loop and
Loop Emulators
Point to Point:
Toll Transponders
and AVI
Wireless: Cellular Phone
Signatures and Beacons
Notation
l
t
w
Data At fixed points 1. Flows (Volumes)
2. Occupancies
3. Time mean speed
Between fixed points
Travel times
Lane changes
Within range of reader (a) Travel times
(b) Space mean speed
(c) Many vehicles exhibit activity
changes
Sensors Inductive loops
Infrared
Video image
processors
Microwave radar
Acoustic
Electronic toll and traffic management transponders
Commercial
AVI systems
Cellular
phone
positioning
systems:
1. Network-
based
2. “Quick
GPS”
3. Pattern
matching
1. Vehicle beacons (as for driver info systems)
2. GPS probes