Modelling Free-flow Speeds on Urban Roads Under Heterogeneous Traffic Conditions

Modelling Free-flow Speeds on Urban Roads underHeterogeneous Traffic Conditions

(M.S. Seminar)

April 24, 2015

Srijith BalakrishnanCE12S021

Research Guide: Prof. R. Sivanandan

Department of Civil EngineeringIndian Institute of Technology Madras

Chennai, India

54

Introduction

LiteratureReview

Objectivesof the Study

DataCollection &Extraction

Analysis ofFree-flowSpeeds

Free-flowSpeedPredictionModels

Summary ofthe Study

Overview

Introduction

Literature Review

Objectives of the Study

Data Collection & Extraction

Analysis of Free-flow Speeds

Free-flow Speed Prediction Models

Summary of the Study

54

2Introduction

LiteratureReview





Summary ofthe Study

IntroductionFree-flow condition

I Free-flow condition refers to very low or zero volume of traffic

(www.shutterstock.com)

I Impedance due to adjacent vehicles is minimumI Greater freedom for drivers to choose the driving speed and lateral

position (lane position)

54

3Introduction

LiteratureReview





Summary ofthe Study

IntroductionFree-flow speed and applications

What is Free-flow speed?

I During free-flow conditions, drivers choose their desired speed

I Definition (Highway Capacity Manual 2010):“the average speed of vehicles on a given facility, measuredunder low volume conditions, when the drivers tend to driveat their desired speed and not constrained by control delay.”

.

Why is Free-flow speed important?

I Quantification of congestion, air quality, fuel consumption, delays, etc.I Classification of streets, selection of speed limits, etc.I Studies on driver behaviour, effect of road geometry, road factors,

environmental factors, etc.

54

4Introduction

LiteratureReview





Summary ofthe Study

IntroductionFree-flow speed models

How are Free-flow speeds estimated?

I Manual estimation (Collecting vehicle speeds from the field during lowvolume hours)

I Estimation using Free-flow speed models (eg: Highway CapacityManual methods)

When are Free-flow speed models important?

I Studies on larger road networks—manual estimation requiresconsiderable amount of capital, human resource and time

I Site or weather conditions not favourable for data collectionI Inadequate technology for automatic speed detection

54

5Introduction

LiteratureReview





Summary ofthe Study

Literature ReviewFree-flow speed factors

I Studies on factors influencing free-flow speed are important fordeveloping statistical models.

I Major governing factors:

Vehicle characteristics : Class, gross weight, engine characteristics, etc.

Road factors : Carriageway width, side clearance, landuse, etc.

Geometric factors : Horizontal and vertical grade, radius of curvature, etc.

Control factors : Intensity of signalized intersections, roundabouts, etc.

Environmental factors : Precipitation rate, visibility, snow, etc.

Driver characteristics : Age, gender, experience, stress level, etc.

54

Introduction

6LiteratureReview





Summary ofthe Study

Literature ReviewPrevious studies on free-flow speed factors

Authors Free-flow speed factors investigated Type of facility

Homogeneous TrafficYagar and Van Aerde (1983) Speed limit landuse lane width gradient of road Rural highways

Dixon et. al (1999) Speed limit access density vertical grade Rural highways

Figueroa and Tarko (2005) Geometric characteristics Rural highwaysBaruzzi et. al. (2008) Vertical gradient lighting conditions Rural freeways

Himes and Donnell (2010) Posted speed limit access density intensity of intersection Urban highwaysSaifizul et. al (2011) Gross vehicle weight Rural highwaysDeardoff et. al. (2011) Posted speed limit Rural highwaysDe Luca et. al. (2012) Slope curvature tortuousness width of road section Rural motorwaysMoses and Mtoi (2013) Speed limit proportion of kerb proportion of restrictive median Urban arterials

Heterogeneous TrafficKadiyali et. al (1983) Vehicle class Rural highwaysBang et. al (1995) Lane width road functional class Urban roadsQureshi et. al. (2005) Radius of curvature length of curve deflection angle Rural highways

Tseng et. al (2005) Speed limit lane width spacing of signalized intersection Rural highways

Yusuf (2010) Drivers’ age vehicle occupancy age of vehicles road geometry Urban arterials

Madhu et. al. (2011) Number of lanes roadway roughness vehicle class Rural highwaysTseng et. al. (2013) Intersection spacing lane width speed limit Urban arterials

I Fewer studies in urban roads under heterogeneous traffic

54

Introduction

7LiteratureReview





Summary ofthe Study

Literature ReviewExisting free-flow speed models for urban roads

I Highway Capacity Manual (Transportation Research Board, 2010)

FFS = fn(speed limit , cross section, section length, access points)

I Homogeneous traffic conditions

I Indonesian Highway Capacity Manual (Director General ofHighways, 1997)

FFS = fn(Base FFS, lane width, side friction, road class)

I Free-flow speed models only for light vehiclesI Base free-flow speed values for other vehicle types

I Tseng et. al. (2013)

FFS = fn(speed limit)

I Lane-wise and class-wise (motor cycles and small vehicles) models forurban roads in Taiwan

54

Introduction

8LiteratureReview





Summary ofthe Study

Literature ReviewWhy is the current study essential?

I Indian urban traffic characteristics are considerably different from thatof developed nations

1. Presence of various classes and subclasses of vehicles inconsiderable proportions

2. Non–adherence to legal speed limits3. Extremely varying road and landuse conditions

I Lack of studies about various road and vehicle factors affectingfree-flow speed under urban traffic conditions in India.

54

Introduction

LiteratureReview

9Objectivesof the Study




Summary ofthe Study

Objectives of the Study

1. To quantify free-flow speeds on various types of urban roads undervarying conditions.

2. To analyse the effect of potential influencing factors on free-flowspeeds of different vehicle classes.

3. To build statistical models for predicting overall and class-wisefree-flow speeds using related influencing factors.

4. To build statistical models for predicting lane choice of drivers underfree-flow conditions using relevant influencing factors.

54

Introduction

LiteratureReview


10DataCollection &Extraction



Summary ofthe Study

Data Collection and ExtractionSelection of Study Sections

I Study conducted on four-lane and six-lane divided roads within urbanareas of Chennai, India.

I Criteria adopted for selecting study sections:1. straight sections with minimum length of 500 m2. no signalized intersections and roundabouts within the sections3. end points of study sections at a minimum distance of 100m from

signalized junctions4. no permanent or temporary speed management structures within

study sections5. plain terrain and good road surface conditions6. no bus-stops within the study sections

54

Introduction

LiteratureReview





Summary ofthe Study

Data Collection and ExtractionSelection of Study Sections

Anna Salai

Hundred Feet Road

New Avadi Road

Poonamallee High Road I

Poonamallee High Road

Sardar Patel Road I

Sardar Patel Road II

Two Hundred Feet Road

East Coast Road

Jawaharlal Nehru Road

Northern Beach Road

Sir Thyagaraja Road

Velachery Main Road I

Velachery Main Road II

Gandhi Mantapam Road

Karunanidhi Salai

Dr Radha Krishnan Sala

i

Tharamani Road I

Tharamani Road II

Greenways Road

Mount Poonamallee HighRoad

Old Mahabalipuram Road I

Old Mahabalipuram Road II

Walajah Road

Road segments considered in the present study (24 nos.)

II

54

Introduction

LiteratureReview





Summary ofthe Study

Data Collection and ExtractionData Collection

Method

1. First phase: Site investigation

2. Second phase: Video data collection

Data Requirements

1. Site factors—carriageway width, link length, side clearance, type ofadjacent landuse, presence of kerb, class of road, type of area,number of access points, etc.

2. Speed, lane position and class of vehicles on various divided urbanroads under free-flow conditions.

Ensuring free-flow condition..

I Speed data collectedI between 3:30 am and 7:30 am (free-flow conditions)I for an average duration of 1.5 hours

54

Introduction

LiteratureReview





Summary ofthe Study


Site details of study sections

Site ID Link Carriage- Side Section Number No. of No. of Road Area Landuse Presencelength way width clearance length of lanes median gaps accesses class type type of kerb

(m) (m) (m) (m) (nos.) (nos.) (nos.)

1 890.00 12.20 8.00 650.00 6 1 2 arterial urban commercial yes2 1730.00 10.65 18.40 455.00 6 0 0 arterial suburban commercial no3 1470.00 7.60 2.50 700.00 4 3 3 subarterial urban residential yes4 1390.00 7.60 4.10 756.00 4 1 0 arterial urban commercial yes5 640.00 7.50 2.40 424.00 4 0 3 arterial urban commercial no6 1920.00 9.70 2.60 610.00 4 0 0 arterial urban institutional yes7 1990.00 8.50 3.00 437.00 4 0 0 arterial urban institutional no8 2610.00 8.70 20.00 1100.00 4 0 0 arterial suburban open area no9 1330.00 7.90 5.00 1100.00 4 2 0 arterial suburban commercial no

10 1020.00 10.95 3.00 670.00 6 0 2 arterial urban residential yes11 760.00 8.60 2.25 525.00 4 0 0 arterial urban commercial no12 1100.00 6.80 6.80 450.00 4 2 2 subarterial urban commercial no13 1740.00 6.45 6.22 463.00 4 1 0 subarterial urban institutional yes14 1740.00 7.50 6.90 463.00 4 1 0 subarterial urban institutional no15 1240.00 8.90 1.95 940.00 4 4 0 arterial urban institutional yes16 910.00 7.20 20.00 910.00 4 0 0 arterial suburban open area no17 800.00 6.90 2.50 570.00 4 1 2 subarterial urban residential yes18 1050.00 9.30 6.45 599.00 6 0 0 arterial urban institutional yes19 980.00 10.42 2.00 374.00 6 0 0 arterial urban commercial no20 1580.00 6.70 2.10 630.00 4 3 1 subarterial urban residential yes21 1870.00 10.30 7.00 707.00 6 1 2 arterial urban institutional no22 1980.00 9.40 11.30 1650.00 6 0 1 arterial urban institutional yes23 1950.00 9.40 10.00 600.00 6 1 0 arterial urban commercial yes24 550.00 8.90 5.20 370.00 6 0 0 subarterial urban residential yes

54

Introduction

LiteratureReview





Summary ofthe Study


Video recording

I Two-camera setup —Vehicle movement at ends of sections recordedsimultaneously

I Data collection under good weather and lighting conditions

54

Introduction

LiteratureReview





Summary ofthe Study

Data Collection and ExtractionData Extraction

I Time stamps of vehicles, class and lane preference details from firstvideo

I Travel time and speed by vehicle matching

Start Point Video End Point Video

54

Introduction

LiteratureReview





Summary ofthe Study

Data Collection and ExtractionData Extraction

I Vehicle classes and subclasses consideredSl. No Class Notation Subclasses

1 Two-wheelers 2W Motor Bike, Scooter, and Moped2 Three-wheelers 3W Passenger Carrier and Goods Carrier3 Passenger cars Car Hatchback, Sedan, and SUV4 Light commercial vehicles LCV Passenger Carrier and Goods Carrier5 Buses Bus MTC, Interstate and Institutional6 Trucks Truck Trucks

I 17,800 vehicles analysed for the present study

0% 25% 50% 75% 100%Cumulative Percentage

2W 3W Bus Car LCV Truck

36% 8% 8% 33% 10% 5%

I Data collection and extraction phase of study conductedbetween January 2013 and April 2014.

I Data collection effort- large

54

Introduction

LiteratureReview



17Analysis ofFree-flowSpeeds


Summary ofthe Study

Analysis of Free-flow SpeedsFactors affecting free-flow speeds

Vehicle factors

vehicle

class

vehicle

subclass

Road factors

carriageway width

link length

side clearance

number of access pointsroad class

number of lanes

Landuse factors

type of

landuse

area type

Lane preference

lane

preference

of drivers

Speed limit and design

speed

legal speed limit

design speed

Vehicle composition

compositionof vehicle classes

Free flow speed factors considered in the study

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and vehicle class

3W

Truck

Bus

2W

LCV

Car

20 40 60 80 100 120Free−flow Speed (km/h)

CLASS 3W Truck Bus 2W LCV Car

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and vehicle subclass

Goods Cr.Passenger Cr.

TruckMTC

InstitutionalInterstate

MopedScooter

BikeLCVGoods Cr.

LCVPassenger Cr.Hatchback

SUVSedan

20 40 60 80 100 120Free−flow Speed (km/h)

CLASS2W 3W Bus Car LCV Truck

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and vehicle class

I Mean free-flow speeds in ascending order: three-wheelers, trucks,buses, two-wheelers, LCVs and passenger cars.

I Findings from statistical tests:1. Among two-wheelers, motor bikes (49.2 km/h) are the fastest

followed by scooters (43.6 km/h) and mopeds(36.0 km/h).2. Among passenger cars, sedans and SUVs have similar speeds

(62.0 km/h and 61.8 km/h respectively), followed by hatchbacks(60.6 km/h).

3. Among LCVs, passenger carriers (57.3 km/h) are faster thangoods carriers (50.5 km/h).

4. Among buses, interstate buses have highest speed (53.3 km/h)followed by institutional buses(48.6 km/h) and MTC buses (42.3km/h).

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and landuse

0

20

40

60

80

100

120

2W 3W Bus Car LCV TruckVehicle Class

Fre

e−flo

w S

peed

(km

/h)

commercial institutional open.area residential

Four-lane roads

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

commercial institutional residential

Six-lane roads

I Four types of landuse –open area (2 sections), institutional (8),residential (5) and commercial (9).

I Mean free-flow speeds: open area (62.4 km/h) , institutional (54.6km/h), commercial (50.9 km/h) and residential (44.0 km/h).

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and area type

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

suburban urban

I Two types of roads according to intensity of adjacent landusedevelopment: urban (20 sections) and suburban (4).

I Mean free-flow speeds: urban (50.9 km/h) and suburban (58.2 km/h).

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and number of lanes

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

Four−lane Six−lane

I Two types of roads according to number of lanes:four-lane divided roads (13 sections) and six-lane divided roads (9).

I Average free-flow speeds: four-lane divided roads (52.8 km/h) andsix-lane divided roads (46.2 km/h).

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and road class

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

arterial subarterial

Four-lane roads

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

arterial subarterial

Six-lane roads

I Two road classes–arterials (17 sections) and subarterials (7).I Mean free-flow speeds: arterials (54.6 km/h) and subarterials (42.7

km/h)

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and presence of kerb

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

Kerb absent Kerb present

Four-lane roads

0

20

40

60

80

100

120


Fre

e−flo

w S

peed

(km

/h)

Kerb absent Kerb present

Six-lane roads

I 13 sections with kerbs, 11 without kerbs.I Mean free-flow speeds: roads with kerb (48.9 km/h) and roads without

kerb (47.9 km/h).I Different effects of kerb on four- and six-lane divided roads.

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and lane preference

0

20

40

60

80

100

120

2W 3W Bus Car LCV TruckVehicle class

Spe

ed (

km/h

)

LANE Kerb lane Median lane

Four-lane roads

0

20

40

60

80

100

120

2W 3W Bus Car LCV TruckVehicle class

Spe

ed (

km/h

)

LANE Kerb lane Middle lane Median lane

Six-lane roads

I On four-lane divided roads, average free-flow speed on kerb lane andmedian lane are 46.4 km/h and 50.4 km/h respectively.

I On six-lane divided road, average free-flow speed on kerb lane,middle lane and median lane are 47.3 km/h, 55.1 km/h and 60.8 km/hrespectively

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsLane preference of vehicle classes

I Free-flow speeds on kerb lanes are lower compared to the inner lanes.I All vehicle classes travel at a lower speed on kerb lane compared

to the inner lanes.I Can it be because more number of slow moving drivers choose

kerb lane?

0

10

20

30

40

50

60

70

80

90


Per

cent

age

(%)

LANE Kerb lane Median lane

Four-lane roads

0

10

20

30

40

50

60

70

80

90


Per

cent

age

(%)

LANE Kerb lane Middle lane Median lane

Six-lane roads

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsLane preference of vehicle classes

I Four-lane roads: Less aggressive vehicles choose kerb lane whereasaggressive vehicles choose median lane

I Six-lane roads: A large proportion of vehicles from all classes choosemiddle lane

I Less aggressive drivers prefer kerb lane over median lane whileaggressive drivers prefer median lane over kerb lane

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsEffect of other road factors

30

40

50

60

70

80

6 8 10 12Carriageway width (m)

Ove

rall

FFS

(km

/h)

FFS = 16.19 + 3.77× CWAY.WIDTH 30

40

50

60

70

80

0.5 1.0 1.5 2.0 2.5Link Length (km)

Ove

rall

FFS

(km

/h)

FFS = 36.87 + 8.35 × LINK.LNGTH

30

40

50

60

70

80

0 5 10 15 20Side clearance (m)

Ove

rall

FFS

(km

/h)

FFS = 42.16 + 1.02 × SIDE.CLEAR 30

40

50

60

70

80

0 1 2 3Number of access points

Ove

rall

FF

S (

km/h

)

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsCompliance with speed limit and design speed

I The legal speed limit on roads within the city boundaries is 40km/h.

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80 100

Free−flow speed (km/h)

Cum

ulat

ive

prop

ortio

n


Subarterial roads

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80 100

Free−flow speed (km/h)

Cum

ulat

ive

prop

ortio

n


Arterial roads

I Percentage of vehicles preferred to travel at a speed > 40km/h: 71% oftwo-wheelers, 45% of three-wheelers, 72% of buses, 93% of cars, 83%of LCVs and 70% of trucks.

54

Introduction

LiteratureReview





Summary ofthe Study

Analysis of Free-flow SpeedsFree-flow speed and vehicle composition

FFS = 52.74 - 0.12×PERCT.2W

30

40

50

60

70

80

0 25 50 75 100Percentage of 2W

Ove

rall

Spe

ed (

km/h

)

2W

FFS = 51.45 - 0.33×PERCT.3W

30

40

50

60

70

80

0 20 40 60Percentage of 3W

Ove

rall

Spe

ed (

km/h

)

3W

FFS = 39.52 + 0.27×PERCT.CAR

30

40

50

60

70

80

0 25 50 75 100Percentage of Car

Ove

rall

Spe

ed (

km/h

)

Car

FFS = 47.40 + 0.11×PERCT.LCV

30

40

50

60

70

80

0 10 20 30 40 50Percentage of LCV

Ove

rall

Spe

ed (

km/h

)

LCV

FFS = 50.70 - 0.28×PERCT.BUS

30

40

50

60

70

80

0 10 20 30 40Percentage of Bus

Ove

rall

Spee

d (k

m/h

)

Bus

FFS = 53.10 - 0.25×PERCT.TRUCK

30

40

50

60

70

80

10 20 30Percentage of Truck

Ove

rall

Spe

ed (

km/h

)Truck

54

Introduction

LiteratureReview




32Free-flowSpeedPredictionModels

Summary ofthe Study

Free-flow Speed Prediction ModelsRegression analysis

Modelling free-flow speeds..

I Prediction models developed for two-minute free-flow speeds usingmultiple linear regression (MLR).

Two minute Free-flow Speeds

Vehicle composition

Road factors

Landuse factors

I Ordinary least squares (OLS) method to estimate the parameters.I Two purposes of model development:

1. predict free-flow speeds on new road segments2. study individual effects of factors under consideration.

54

Introduction

LiteratureReview





Summary ofthe Study

Free-flow Speed Prediction ModelsSelection of model specifications

I Selection of predictor variables based on correlation among theconsidered factors.

I Three model specifications for general free-flow speed models forurban roads (four- and six-lane roads combined)

I Two model specifications for separate free-flow speed models for four-and six-lane urban roads

54

Introduction

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Summary ofthe Study

Free-flow Speed Prediction ModelsOverview of general models developed

54

Introduction

LiteratureReview





Summary ofthe Study

Free-flow Speed Prediction ModelsBasic Models (BM)

BM1 BM2 BM3

Estimate Std. Error t-stat Estimate Std. Error t-stat Estimate Std. Error t-stat

(Intercept) 8.264 1.473 5.611 9.370 2.180 4.297 8.506 1.526 5.575CWAY.WIDTH 3.459 0.153 22.594 3.158 0.221 14.322 3.558 0.148 23.982SIDE.CLEAR 0.626 0.049 12.741 0.394 0.063 6.292 – – –LINK.LNGTH 5.163 0.499 10.348 5.362 0.479 11.204 5.014 0.486 10.322ACCESS.NUM -0.731 0.228 -3.202 – – – – – –SUBARTERIAL – – – -2.048 0.675 -3.034 – – –SUBURBAN – – – 7.855 0.887 8.855 8.815 0.908 9.708KERB – – – 2.759 0.493 5.598 3.781 0.536 7.049RESIDENTIAL – – – – – – -4.754 0.676 -7.037COMMERCIAL – – – – – – -1.559 0.579 -2.691OPEN.AREA – – – – – – 5.210 1.187 4.388

R2 0.639 0.693 0.712F–stat 271.336 229.536 215.651Significance of F 0.000 0.000 0.000

54

Introduction

LiteratureReview





Summary ofthe Study

Free-flow Speed Prediction ModelsClass-wise Models (CM)

I Specification 1

CM1.2W CM1.3W CM1.CAR CM1.LCV CM1.BUS CM1.TRUCK

(Intercept) 17.985 14.013 11.936 14.628 9.690 23.396CWAY.WIDTH 3.326 2.287 4.985 3.351 4.434 2.236SIDE.CLEAR 0.633 0.408 0.841 0.816 0.467 0.360LINK.LNGTH 2.225 2.441 4.030 3.255 3.336 0.558ACCESS.NUM -0.268 -0.530 -1.221 -1.742 -1.839 -0.820

R2 0.438 0.367 0.484 0.400 0.335 0.180F–stat 118.039 62.271 140.914 74.477 52.211 15.12Significance of F 0.000 0.000 0.000 0.000 0.000 0.000

I Specification 2


(Intercept) 24.979 14.738 9.127 10.177 12.688 25.582CWAY.WIDTH 1.456 2.341 4.086 3.262 2.597 1.741SIDE.CLEAR 0.589 0.329 0.213 0.468 0.138 0.334LINK.LNGTH 2.738 2.792 6.028 4.375 4.777 0.776SUBARTERIAL -3.616 -1.344 -2.167 -1.503 -4.789 -2.425SUBURBAN 3.568 2.505 17.137 11.418 14.714 2.959KERB 1.955 -0.668 3.608 3.852 4.881 2.459

R2 0.478 0.384 0.597 0.445 0.465 0.189F-stat 92.220 44.550 148.000 59.390 59.770 10.640Significance of F 0.000 0.000 0.000 0.000 0.000 0.000

54

Introduction

LiteratureReview





Summary ofthe Study

Free-flow Speed Prediction ModelsClass-wise Models (CM)

I Specification 3


(Intercept) 18.917 15.716 7.601 10.088 9.063 24.149CWAY.WIDTH 2.287 2.539 4.37 3.615 3.298 2.212LINK.LNGTH 3.495 2.244 5.811 4.245 3.360 0.210RESIDENTIAL -4.450 -4.391 -4.369 -4.629 -6.643 -6.783COMMERCIAL -0.659 -1.382 -0.572 -1.744 -2.333 -1.816OPEN.AREA 5.733 7.364 1.549 6.684 -4.871 2.003SUBURBAN 6.049 2.318 18.461 12.21 17.970 5.443KERB 3.065 0.325 4.794 4.763 6.030 3.685

R2 0.466 0.423 0.605 0.456 0.480 0.211F–stat 75.395 44.764 130.864 53.172 54.374 10.421Significance of F 0.000 0.000 0.000 0.000 0.000 0.000

I Class-wise models suggest that:1. the site factors influencing free-flow speeds depend largely on the

class of vehicle.2. the influence of most of the site factors are insignificant in trucks.

54

Introduction

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Summary ofthe Study

Free-flow Speed Prediction ModelsCombined Model

I Overall speed of a stream consisting of several substreams is given by:

vs =∑

pi vi

I Similarly, overall free-flow speeds can be estimated by combiningclass-wise free-flow speeds.

FFS = (p2W × FFS2W ) + (p3W × FFS3W ) + (pCAR × FFSCAR) + (pLCV × FFSLCV )

+ (pBUS × FFSBUS) + (pTRUCK × FFSTRUCK )

I Free-flow speeds computed using Class-wise Models (CM3.x).I Vehicle proportions obtained from vehicle composition data.I R2 value of Combined Model: 0.720.

54

Introduction

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Summary ofthe Study

Free-flow Speed Prediction ModelsOverview of models for four- and six-lane divided roads

54

Introduction

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Summary ofthe Study

Free-flow Speed Prediction ModelsBasic Models (BM) for four- and six-lane roads

BM1.4L BM1.6L

Estimate Std. Error t-stat Estimate Std. Error t-stat

(Intercept) 8.935 2.275 3.928 -14.115 5.295 -2.666CWAY.WIDTH 4.576 0.273 16.776 5.432 0.392 13.865LINK.LNGTH 4.771 0.537 8.886 6.022 0.828 7.278INSTITUTIONAL 2.681 0.665 4.034 3.149 0.915 3.442OPEN.AREA 5.962 0.967 6.164 NA NA NARESIDENTIAL 0.653 0.659 0.991 -4.306 1.190 -3.619URBAN -8.167 0.837 -9.759 -6.591 2.444 -2.697KERB – – – 11.363 0.825 13.779

R2 0.776 0.705F-stat 236.100 78.100Significance of F 0.000 0.000

BM2.4L BM2.6L

Estimate Std. Error t-stat Estimate Std. Error t-stat

(Intercept) -9.739 1.990 -4.894 -18.599 4.270 -4.356CWAY.WIDTH 5.856 0.269 21.741 5.073 0.352 14.421LINK.LNGTH 4.655 0.533 8.732 5.749 1.056 5.447SIDE.CLEAR 0.732 0.045 16.213 0.700 0.162 4.326KERB – – – 8.161 0.967 8.438

R2 0.733 0.673F-stat 376.700 101.900Significance of F 0.000 0.000

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Summary ofthe Study

Free-flow Speed Prediction ModelsClasswise Models (CM) for four-lane roads

CM1.4L.2W CM1.4L.3W CM1.4L.CAR CM1.4L.LCV CM1.4L.BUS CM1.4L.TRUCK

(Intercept) 20.782 11.512 18.688 12.236 2.935 18.299CWAY.WIDTH 2.847 2.657 5.583 4.920 5.670 3.920LINK.LNGTH 3.090 5.194 5.115 3.465 5.949 –INSTITUTIONAL 0.751 0.603 3.269 3.643 – –OPEN.AREA 6.182 8.720 0.519 7.776 – –RESIDENTIAL -1.163 -3.344 1.981 1.284 – –URBAN -5.141 -1.634 -19.124 -11.352 -13.576 -6.574KERB – – – – – –

R2 0.527 0.469 0.664 0.572 0.616 0.240F-stat 75.030 51.300 131.100 64.350 144.100 26.840Sign. of F 0.000 0.000 0.000 0.000 0.000 0.000


(Intercept) 5.892 -0.246 -12.108 -11.395 -15.851 8.763CWAY.WIDTH 3.983 3.972 7.165 6.404 6.538 4.151LINK.LNGTH 2.330 4.591 4.538 3.496 5.767 –SIDE.CLEAR 0.671 0.552 1.010 1.003 0.587 0.409KERB – -1.841 – – -2.908 –

R2 0.505 0.458 0.540 0.517 0.470 0.233F-stat 138.200 61.590 156.800 104.000 59.490 25.760Sign. of F 0.000 0.000 0.000 0.000 0.000 0.000

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Summary ofthe Study

Free-flow Speed Prediction ModelsClasswise Models (CM)for six-lane roads


(Intercept) 11.474 1.176 -17.870 -13.659 -27.953 42.767CWAY.WIDTH 3.029 3.601 6.633 4.706 5.370 –LINK.LNGTH 4.420 – 7.564 7.783 5.474 –INSTITUTIONAL 2.485 3.555 0.848 0.384 4.895 –OPEN.AREA NA NA NA NA NA NARESIDENTIAL -4.827 -1.831 -6.371 -3.857 -0.854 –URBAN -8.225 – -7.805 – – –KERB 10.102 4.982 13.310 12.707 15.947 8.484

R2 0.421 0.309 0.598 0.303 0.416 0.169F-stat 23.550 14.870 48.150 13.030 20.700 20.630Sign. of F 0.000 0.000 0.000 0.000 0.000 0.000


(Intercept) 4.154 4.141 -28.847 6.510 -8.163 42.767CWAY.WIDTH 2.787 3.276 6.722 3.217 3.839 –LINK.LNGTH 3.560 – 5.724 – – –SIDE.CLEAR 0.812 0.719 1.005 1.212 1.082 –KERB 6.384 – 8.968 8.257 12.239 8.484

R2 0.398 0.278 0.596 0.304 0.389 0.169F-stat 32.460 26.010 72.270 152.000 22.600 20.630Sign. of F 0.000 0.000 0.000 0.000 0.000 0.000

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Summary ofthe Study

Free-flow Speed Prediction ModelsValidation of developed models

I Sample allocation: Model development (70%), Model Validation (30%).I Mean Absolute Percentage Error (MAPE) calculated after comparing

predicted and observed free-flow speeds.

MAPE =100n

∑∣∣∣∣ yobserved − ypredicted

yobserved

∣∣∣∣I MAPE values obtained for general models

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Summary ofthe Study

Free-flow Speed Prediction ModelsValidation of developed models

I Sample allocation: Model development (70%), Model Validation(30%).

I Mean Absolute Percentage Error (MAPE) calculated aftercomparing predicted and observed free-flow speeds.

MAPE =100n

∑∣∣∣∣ yobserved − ypredicted

yobserved

∣∣∣∣I MAPE values obtained for developed models

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45Summary ofthe Study


1. The variation in free-flow speeds on Chennai roads is considerable.Lowest speed reported is 16 km/h,whereas the highest speed is 137km/h.

2. Significant variations in mean free-flow speeds is observed acrossvehicle classes and subclasses.

I Vehicle class: fastest- passenger cars, slowest- three-wheelers.I Vehicle subclass: fastest- sedans, slowest- mopeds.

3. Significant influence of road and landuse factors on free-flow speeds isconfirmed using statistical tests.

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4. Along with other factors, the lane choice of drivers also influences thefree-flow speeds.

I In most of the cases, higher speeds are observed on the innerlane(s) and slower speeds on kerb lane.

I Unique patterns in lane choice: Slow-moving and smaller vehiclesprefer kerb lane, whereas fast moving and larger vehicles preferinner lanes.

5. Two sets of regression models were developed for free-flow speedprediction.

I Basic Models (BM): road and landuse factorsI Class-wise Models (CM): road and landuse factors

6. Classwise Models(CM) confirm that the effect of road and landusefactors are different across vehicle classes. Trucks least affected byfactors considered in the study.

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7. Model results: Effect of various factors on free-flow speed:-I Higher free-flow speed–higher carriageway width, link length

and side clearance, presence of kerb, suburban areas, arterialroads, open areas, institutional areas.

I Lower free-flow speed–higher number of access points,absence of kerb, urban areas, subarterials, commercial areas,residential areas.

8. Developed models could be used in planning and operational analysisof urban road facilities under heterogeneous traffic conditions.

9. Lane choice models under free-flow conditions have been alsodeveloped as part of the study

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Scope for Future Research

I Present study focuses only on divided urban roads. Free-flow speedson undivided roads are not considered

I Even in a given study section and a vehicle class, the speed variationsare significant. This hints at possible influence of driver characteristics.

I Effect of trip characteristics such as trip length, purpose, etc. may haveinfluence on individual speeds

I The present study is conducted on mid-block sections. Studying theinfluence of signalized intersections may be instrumental in developingmodels to predict free-flow speeds of links and paths.

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Acknowledgements

1. Centre of Excellence in Urban Transport (CoEUT), IIT Madras

2. Mr. Sivakirubanandhan and Mr. G. Arivazhagan, Project staff, CoEUT,IIT Madras

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Visible Output

1. Balakrishnan, S., R. Sivanandan. (2014). "Lane Choice Behaviour of Vehicleson Urban Roads under Free-flow Conditions". Proceedings of the InternationalConference on Recent Trends and Challenges in Civil Engineering–RTCCE2014 (CD-ROM), Motilal Nehru National Institute of Technology, Allahabad,India, December 12-14.

2. Balakrishnan, S., R. Sivanandan. “Influence of Lane and Vehicle Subclass onFree-flow Speeds for Urban Roads in Heterogeneous Traffic.” (Accepted forpresentation at the 18th Meeting of the European Working Group onTransportation–EWGT 2015 to be held at Delft, The Netherlands from July 14 -16, 2015)

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Selected References

1. Bang, K.L., Carlsson, A., Palgunadi, 1995. Development of Speed-Flow Relationships for Indonesian Rural Roads UsingEmpirical Data and Simulation. Transportation Research Record.

2. Baruzzi, A., Galarraga, J., Herz, M., 2008. Effects of Grades and Visibility on Freeway Free-Flow Speeds, in: Sixth InternationalConference of Traffic and Transportation Studies Congress (ICTTS), American Society of Civil Engineers, Nanning, China. pp.956–966.

3. De Luca, M., Lamberti, R., DellAcqua, G., 2012. Freeway Free Flow Speed: a Case Study in Italy, in: 15th Meeting of the EUROWorking Group on Transportation, Paris, France. pp. 628–636.

4. Deardoff, M.D., Wiesner, B.N., Fazio, J., 2011. Estimating Free-Flow Speed from Posted Speed Limit Signs, in: 6th InternationalSymposium on Highway Capacity and Quality of Service, Stockholm , Sweden. pp. 306–316.

5. Directorate General of Highways, Indonesian Highway Capacity Manual. Ministry of Public Public Works, Jakarta, Indonesia,1997.

6. Dixon, K.K., Wu, C.H., Sarasua, W., Daniel, J., 1999. Posted and Free-Flow Speeds for Rural Multilane Highways in Georgia.Journal of Transportation Engineering 125, 487–494.

7. Figueroa, A.M., Tarko, A.P., 2005. Speed Factors on Two-lane Rural Highways in Free-Flow Conditions. TransportationResearch Record: Journal of the Transportation Research Board , 39–46.

8. Himes, S., Donnell, E., 2010. Speed Prediction Models for Multilane Highways: Simultaneous Equations Approach. Journal ofTransportation Engineering 136, 855–862.

9. Kadiyali, L., Viswanathan, E., Gupta, R., 1983. Free Speeds of Vehicles on Indian Roads. Journal of Indian Road Congress 42.10. Madhu, E., Velmurugan, S., Ravinder, K., Nataraju, J., 2011. Development of free-speed equations for assessment of road-user

cost on high-speed multi-lane carriageways of India on Plain Terrain. Current Science 100, 1362–1372.11. Moses, R., Mtoi, E., 2013. Evaluation of Free Flow Speeds on Interrupted Flow Facilities. Technical Report. Department of Civil

Engineering, FAMU-FSU College of Engineering. Tallahassee, United States.12. Qureshi, A.S., Khakheli, G.B., Memon, R.A., 2005. Operating Speed Prediction Model for Existing Two Lane Two-Way Old

Alignments. Mehran University Research Journal of Engineering & Technology 24, 377–386.13. Tseng, P.Y., Lin, F.B., Chang, C.W., 2013. Analysis of Free-Flow Speed Characteristics of Urban Arterials. Asian Transport

Studies 2, 363–378.14. Transportation Research Board. Highway Capacity Manual. Washington D. C., United States. 201015. Tseng, P.Y., Sheikh, S., Lin, F.B., 2005. Estimation of Free-Flow Speeds for Multilane Rural and Suburban Highways. Journal of

East Asian Society of Transportation Studies 6, 1484–1495.16. Yagar, S., Van Aerde, M., 1983. Geometric and Environmental Effects on Speeds of Two-lane Highways. Transportation

Research Part A: Policy and Practice 17A, 315–325.17. Yusuf, I.T., 2010. The Factors For Free-Flow Speed On Urban Arterials Empirical Evidences From Nigeria. Journal of American

Science 6, 1487–1497.

Thank you.

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Free-flow Speed Prediction ModelsChecking assumptions of regression models

I Histogram of Residuals: normality of residualsI Scatter plot of residuals versus Predicted values: presence of

heteroscedasticityI Scatter plot of studentized residuals versus predicted values:

presence of outliersI Cook’s distance: Presence of influential points

Di =

∑(Yj − Yj(i))

2

p × MSE

I Variance Inflation Factor (VIF): multicollinearity

VIF =1

1 − R2i

I Durbin Watson test: Autocorrelation

DW statistic, d =

∑Ti=2(εi − εi−1)

2∑Ti=2 ε

2t

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Free-flow Speed Prediction ModelsSample check for regression assumptions (BM3)

0

20

40

60

−20 −10 0 10 20Residual (km/h)

Fre

quen

cy

−20

−10

0

10

20

40 50 60Predicted Speed (km/h)

Res

idua

l (km

/h)

−2

0

2

40 50 60Predicted Speed (km/h)

Stu

dent

ized

Res

idua

l

0.00

0.01

0.02

0.03

0.04

0.05

0 200 400 600Observation Number

Coo

k's

dist

ance

VIF CWAY.WIDTH LINK.LNGTH SUBURBAN LANDUSE KERB1.18 1.45 2.49 4.42 1.73

DW Statistic 1.89

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Analysis of Free-flow SpeedsFree-flow speed and lane preference

I Four-lane roads: Are free-flow speds of LCVs and cars indeed higheron kerb lane? No, not always!

I Results of t-tests conducted for individual four-lane divided sections(median lane versus kerb lane)

−5

0

5

10

15

3 4 5 6 7 8 9 11 12 13 14 15 16 17 20Site ID

Mea

n di

ffere

nce

(km

/h)

not significant significant

Car

−5

0

5

10

15

3 4 5 6 7 8 9 11 12 13 14 15 16 17 20Site ID

Mea

n di

ffere

nce

(km

/h)

not significant significant

LCV

I In most locations, free-flow speeds are higher on median lanes(contrary to the earlier observation)

Modelling Free-flow Speeds on Urban Roads Under Heterogeneous Traffic Conditions

Engineering

Transcript of Modelling Free-flow Speeds on Urban Roads Under Heterogeneous Traffic Conditions