Traffic Engineering

Topic: Traffic Studies & Data Collection

Henry Liu

CE 4211/5211 – Traffic Engineering

University of Minnesota

email: henryliu@umn.edu

Shockwaves signalized intersections

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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

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

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

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

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

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

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)

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

Traffic Counts Displayed in a Network

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

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)

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.)

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

Vehicle Mile Travel (VMT)

ADT x roadway length

Applications:

Economic evaluation

Resource allocation (maintenance &

improvement)

Planning

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

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

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))

Flow Measurement Techniques

Manual count board

Laptop & software program

Handheld electronic device

Pneumatic tubes

Inductance loop detectors

Video Imaging Analysis

Manual Count Board

JAMAR Handheld Devices

Software Program

Pneumatic Road Tubes

Inductance Loops

Bike LoopsVehicle Loops

Inductance Loop Signatures (1)

Sport Car

Truck

Inductance Loop Signatures (2)

Pickup Truck

Trash Truck

Inductance Loop Signatures (3)

Tailgating

vehicles

Vehicle with

a boat

Video Imaging

Video camera

Video Imaging

Autoscope hardware

Video Imaging

Autoscope software

Speed Data Collection

Radar gun

Inductance loop detectors

Single loop

Double loop

Video imaging

Radar Guns

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

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

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

Travel Time Measurement Techniques

Floating Car

License plate matching

Automatic Vehicle Location (AVL)

Global Positioning Systems (GPS)

Cellular Phones

Automatic Vehicle Identification (AVI)

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

License Plate Matching

Global Positioning System (GPS)

• GPS Time

• Latitude and Longitude

• Speed

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

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

Electronic Toll Collection

Origin-Destination (O-D) Studies

Determining the percentage of all traffic traveling from each origin point of interest to each destination point of interest

<<

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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

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2 3

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Study AreaZ1

Z2

O-D Measurement Techniques

Roadside Interview

Postcards

License Plate Matching

Vehicle Re-Identification Technology

Vehicle Re-Identification Technology

Alton

ICD

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

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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