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1972

A study on the lateral placement of automobiles due to A study on the lateral placement of automobiles due to

restrictions on two-lane rural highways restrictions on two-lane rural highways

Warren Chip Woods

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A STUDY ON THE LATERAL PLACEMENT OF AUTOMOBILES

DUE TO RESTRICTIONS ON TWO-LANE RURAL HIGHWAYS

BY

WARREN CHIP WOODS, 1948-

A THESIS

Presented to the Faculty of the Graduate School of the

UNIVERSITY OF MISSOURI-ROLLA

ln. Partial Fulfillment of the Requirements for the Degree

MASTER OF SCIENCE IN CIVIL ENGINEERING

1972

Approved by

T2719 54 pages c. I

ABSTRACT

The driver of an isolated vehicle on a given section

of highway, whether it is urban or rural, will choose a

path on the pavement that offers the least resistance to

driver effort and which to him seems safest. Lateral

obstructions, such as retaining walls, trees, bridge

abutments, ect., which may cause him to deviate from the

desired path represent some degree of hazard to the

driver and should be removed, if practicle.

ii

The purpose of this investigation was to determine

any change in the lateral placement of automobiles due to

side restrictions on rural two-way, two-lane highways.

Phase one of the study concerned two bridges on u.s. Highway 63 near Rolla, Missouri, that differed only in the

amount of lateral clearance between the edge of the

traffic lane and its corresponding bridge abutment. Phase

two of the investigation concerned a bridge near Newburg,

Missouri, and the change caused by reflectorizing the

bridge abutments for better night visibility.

The results of phase one showed that by increasing

the amount of offset between the traffic lane edge and the

bridge abutment, drivers positioned their vehicle more

correctly within their lane. For the purpose of this in­

vestigation, a vehicle is considered correctly positioned

within its lane when the vehicle is centered in the lane;

that is, there is an equal distance from the pavement

iii

center line to the left edge of the left tire and from the

right edge of the right tire to the right edge of the

traffic lane. In phase two of the investigation, it was

determined that the reflectorization of the bridge abut­

ments was benefitial in that drivers positioned their

vehicle more correctly within its lane.

iv

ACKNOWLEDGEMENTS

The author wishes to thank Dr. James Larry Josey for

his guidance and assistance during the author's graduate

study and while acting as thesis director. Grateful

acknowledgement is also given to Dr. Frank A. Gerig, Jr.

for his guidance, and to Dr. John D. Rockaway for his

assistance in the statistical aspect of the thesis.

TABLE OF CONTENTS

.A.BS !rRA. CT • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

.A.CK:NOILE.OO EMENTS ••••••••••••••••••••••••••••••••••••

LIST OF FIGURES•••••••••••••••••••••••••••••••••••••

LIST OF 'l!ABLES ••••••••••••••••••••••••••••••••••••••

I. IN~RODUOTION ••••••••••••••••••••••••••••••

Background ••••••••••••••••••••••••••••••

Purpose of This Investigation •••••••••••

II • REVIEW OF PREVIOUS RESEARCH •••••••••••••••

Effect of Shoulders •••••••••••••••••••••

Roadway Characteristics ••••••••••.••••••

Bridge Studies ••••••••••••••••••••••••••

v

PAGE

ii

iv

Y1

vii

1

1

2

3

5

7

9

Other Studies........................... 12

III.

IY.

v. VI.

Summar.r. of Review of Previous Research •• ·' ME!HODOLOGY •••••••••••••••••••••••••••••••

!l!ea t Lo ca.t.ions • • • • • • • • .• • • • • • • • • • • •. • • ••••

Field Procedure •••••••••••••••••••••••••

RESULTS •••••••••••••••••••••••••••••••••• •

Results of Phase One ••••••••••••••••••••

Resulta of Phase Two ••••••••••••••••••••

DISCUSSION OF THE RESULTS •••••••••••••••••

CONCLUSIONS AND RECOMMENDATIONS •••••••••••

Conclusions •••••••••••••••••••••••••••••

Recommendations •••••••••••••••••••••••••

LITERA!URE CITED ••••••••••••••••••••••••••••••••••••

VI!A •••• • ••••••••••••••••••••••••••• •. •. • • • • • • • • • • • •

12

14

14

22

27

21

33

40

42

42

43

45

47

vi

LIST OF FIGURES

FIGURE PAGE

1A Map of the Study Area •••••••••••••••••••••• 15

1 Bridge Number One, Located Five Miles North of Rolla, Missouri, on U. s. Highway 63, Looking North •••••••••••••••••• 17

2 Bridge Number !wo, Located Eleven Miles South of Rolla, Missouri, on u. s. Highway 63, Looking West ••••••••••••••••••• 17

3 Plan View of Bridge Number One ••••••••••••• 18

4 One-Half Section A-A of Bridge Number One •• 19

5 Plan View of Bridge Number Two ••••••••••••• 20

6 One-Half Section A-A of Bridge Number Two •• 21

7 Bridge Number !hree, Located 1 • 7 •iles From the Junction of Phelps County Routes P and T, on Route P, LOoking South ••••••••• 23

8 Illustrative Example of the Way Measure-mente Were Made for Both Phases of the study •••••••••••••••••••••••••••••••••••••• 23

9 Section View of Bridge Number !hree •••••••• 24

10 Histograph of the Data Collected at Bridge Number One ••••••••••••••••••••••••••••••••• 29

11 Histograph of the Data Collected at Bridge llllillter ~o ••••••••••••••••••••••••••••••••• 31

12 Histograph of the Data Collected at Bridge Number Three Before Retlectorization ••••••• 35

13 His to graph of the Data Collected at Bridge Number !hree After Reflectorization •••••••• 37

TABLE

1

2

3

4

6

LIST OF TABLES

~,ield .i.>a ta for Bridge Number One •••••••••••

Field Data for Bridge Number Two •••••••••••

One-Way Analysis of Variance Table for Phase One . .........•.•.....................

Field Data for Bridge Number Three Before Reflectorization ••••••••••••••••••••

Field Data for Bridge Number Three

vii

PAGE

28

30

32

34

After Reflectorization..................... 36

One-Way Analysis of Variance Table for Phase Two • ••••••••••••••.•••••••••••••••••• 39

CHAPTER I

INTRODUCTION

Backgrormd

1

The tendency of the driver of an isolated vehicle on

a given section of roadway is to choose a path on the

pavement which requires the minimum amount of driver

effort and which to him seems safest. It is normal

driver behavior to swerve or steer away from objects on

or adjacent to the highway, such as sign posts, retaining

walls, parked automobiles, and bridge abutments. This

path that the vehicle travels can be observed, measured,

and recorded by several methods. One of the most common,

and possibly the easiest method for describing such data

is in terms of transverse or lateral placement of the

vehicle on the highway. Testing proceedures vary, but,

in general, measurements of this lateral placement are

taken from a reference point on the highway pavement to

some arbitrarily designated point on the motor vehicle.

The number of studies conducted in the field of

lateral placement are numerous, with each separate study

being concerned with one or more driver or road character­

istic. Lateral placement studies are just as relevent

today as they were in the early 1940's when a number of

State and Federal agencies were conducting such research.

It is a problem that must be constantly considered with

2

the changing technology in the automotive industry as the

trend in automotive design is for automobiles with wider

tread widths, and in the field of highway design since

the highway designer strives for an optimum design from

the aspects of safety and economy.

Purpose of This Investigation

The purpose of the research conducted during this

investigation was to determine any effect on the lateral

placement of vehicles due to restrictions imposed by

bridge abutments on rural two-way, two-lane highways.

Research was done using a two phase investigation process.

The first phase considered the effect of increasing the

distance between the edge of the traffic lane and the

bridge abutment, and the second phase was concerned with

the change in lateral placement of vehicles caused by

reflectorizing the bridge abutment.

CHAPTER II

REVIEW OF PREVIOUS RESEARCH

!l!he need :for lateral placement studies was recognized

by Holmes and Reymer (1) in early 1940 in their quest for

new techniques in studying traffic behavior. They deter­

mined two reasons why lateral placement data was needed.

l'irs t, to determine economical lane widths :for various

speeds and traffic types: and second, to study the

behavior o:f traffic under Yarious highway and roadside

oondi tiona. !he main purpose of the investigation by

Holmes and Reymer was the determination of the definition

of a well designed road.

According to HOLMES and REIMER (1940, p. 37) "On a well designed road, properly used, this (vehicle) path should parallel the center line, neither swerving toward the edge when meeting vehicles moving in the opposite direction nor veering toward the center wJum passing roadside objects such as culvert headwalls, bridge abut­ments , posts , or trees • "

Holmes and R~er used a placement detector strip to

record lateral placement that consisted of two spring­

steel strips twenty feet lol'lg, separated f~ each other

by means of a rubber arch. !he entire strip was encased

in a rubber housing to prevent damage by inclement

weather conditions. When a vehicle passed over the

detector strip, the arch was depressed, which brought the

two metal strips into contact and completed an electrical

circuit. The strips were divided into one foot segments,

4

with each of these consisting of seven and one-half inches

of "live" section and four and one-half inches of "dead 11

section, so recordings could be made to the nearest foot.

From the results obtained from the investigation, Holmes

and Reymer stated that the required pavement width for

passenger cars would be the sum of the following three

variables:

1. The tread widths of two vehicles when meeting.

2. The amount of clearance between two vehicles

when meeting.

3. An adequate edge clearance for both vehicles.

In 1946, Green (2) devised a new method for recording

lateral placement that utilized an electrically-operated

motion-picture camera. The camera could be mounted out

of sight on highway signs or bridge abutments, and thus

not affect the drivers of the observed vehicles. Green

found that this method had several advantages compared to

the placement detector strip used by Holmes and Reymer.

Some of these advantages are:

1. accuracy

2. ease of changing location

3. absence of visual equipment to distort normal

driver behavior.

4. applicable to both day and night investigations

This method had one weakness, in that readings could

only be made to the nearest six inches at distant stations

and to the nearest three inches at the nearer stations.

These two methods, or modifications thereof, are

still the primary means of collecting lateral placement

data.

Effec~ of Shoulders

One of the primary areas of concern to the highway

design engineer is that of shoUlders. .A.sriel Taragin, a

highway engineer with the Division of Highway Transporta­

tion Research of the Public Roads Administration, was one

of the pioneers in studying the overall effects that

shoulders had on the speed and lateral placement of motor

vehicles.

Taragin conducted three investigations between 1953

and 1957 that considered the effect that shoulders had on

the lateral placement of vehicles. In the first of the

investigations, in 1953, Taragin and Eckhardt ( 3) deriTed

the following conclusions, based on the lateral placement

phase of the investigation:

1. The lateral position of free moving vehicles and

the clearance between meeting vehicles bears no

significant relation to shoulder widths above four

f~et.

5

2. Well-maintained grass shoulders have the same

af:f'ect on lateral placement as well-maintained gravel

shoulders.

In his 1955 investigation, Taragin (4) considered

the effect that objects on highway shoulders had on

driver behavior. Objects selected for the investigation

were a passenger car, a truck, and a barricade, which

were placed at the pavement edge, and at distances of

three and six feet from the edge of the pavement. From

this study, Taragin concluded that:

1. The effect on lateral position was the greatest

when the object was at the pavement edge, and

diminished rapidly with an increase in the distance

of the object from the edge of the pavement.

6

2. The type of object on the shoulder -- car,

truck, or barricade -- caused approximately the same

degree of shifting.

Taragin's third study (5), in 1957, considered the

effect that different types and widths of shoulders had

on the lateral placement of vehicles. The types of

shoulders used were gravel shoulders from three to ten

feet wide, a bituminous mixture with gravel, and bitu­

minous-paved shoulders. He found that the average clear­

ance between the bodies of meeting vehicles was approxi­

mately six feet for wide gravel shoulders; about seven

and one-half feet for combined shoulders; and well over

ten feet for bituminous paved sections with matching

traffic lanes and shoulders. Taragin also determined

that the greater the degree of contrast in appearance

between the traffic lane and the shoulders, the greater

the tendency for drivers to operate within the confines of

the traffic lane.

The shoulder investigation conducted by case, et.

al. (6) in 1953 concerned the affect on lateral placement

of different types of roadside structures. The group

used a black hinged plywood structure ~at had expandible

widths of three and one-half, five, and eight feet, with

readings taken when the structure was at distances of

one-half, three, and seven feet from the highway edge.

It was found that even at minimum size and distance con­

ditions, the average amount of deviation from the normal

vehicle path was five inches, and the drivers reaction to

the distance the object was placed from the pavement edge

was of a higher order of magnitude than th'e size of the

object. The investigation also determined that, as the

ob3ect was placed clos.er.:to the pavement edge, the dis­

tance along the roadway before the driver reaChed the

object, and where the maximum reaction occurs, increased.

Roadway Characteristics

7

Another field of interest to the highway designer is

the effect that roadway characteristics have on the

lateral placement of vehicles. In this field, Asriel

Taragin again conducted three research investigations from

1943 to 1947.

In his 1943 study (7), Taragin was concerned with the

effect that the cross section design of the roadway had an

the lateral placement of vehicles. From the information

collected during this investigation, Taragin devised the

~ollowing relationships:

1 • For traffic of predominantly passenger cars, a

20 foot pavement width was adequate.

2. For mixed traffic of passenger cars and some

truck traffic, 22 feet was needed.

3. For areas of high truck traffic, a 24 foot pave­

ment was required.

In his second study on roadway characteristics (8),

Taragin was interested in the effect of roadway width on

vehicle operation. Analyzing his data, Taragin found

that, for pavements of 18, 20, 22, and 24 feet in width,

with an increase in traffic volume, the distance that the

vehicle shifted away from the center line increased; and

that shoulder widths in excess of four feet do not affect

the transverse position of vehicles when there is no

obstruction immediately adjacent to the outside of the

shoulder.

8

In his 1947 investigation of roadside characteristics,

(9), Taragin shifted his attention to the effect that

pavement center lines have on the lateral placement of

vehicles. He used four widths of two-lane roads in this

investigation; 18, 20, 22, and 24 feet. He found that,

for each of the pavement widths studied, the typical

vehicle path is further to the right on pavements with a

center line marking than it is on a similar pavement

9

without center line markings. Upon further examination,

'l!aragin found that vehicles were driven closer to their

proper position on the roadway and encroached on the left

lane less frequently when they have a center line marking

as a guide. For ~aragin's investigation, and for the

remainder of this thesis, a vehicle is considered to be

properly positioned within its lane when the vehicle is

centered in the lane; that is, there is an equal amount of

distance from the pavement center line to the left edge of

the left tire and from the right edge of the right tire to

the right edge of the traffic lane.

A more recent area of concern to the highway depart­

ments is the matter of edge striping and its effect on

traffic operations. In the 1960 investigation by Thomas

and Taylor (10), they found that, on 24 foot wide pave­

ments, the trend of the free-moving vehicle is to travel

nearer to the pavement center line after the painting of

an edge stripe. The 1969 investigation on edge striping

by the Missouri State Highway Department (11) produced

similar results when applied to two-lane, two-way rural

roadways of 24 feet in width.

Bridge Studies

There have been several lateral placement investiga­

tions that dealt with bridges. Green {2) conducted part

of hie test at a bridge location. In 1941, Walker {12)

10

used a lateral placement study to determine a value for

an adequate bridge width. He observed over 20,000

vehicles on eleven bridges in a survey in the states of

Ohio, Illinois, Iowa, and Oregon. After he analyzed the

data, Walker derived an equation for required bridge

width that included the following variables:

1. The distance freely moving vehicles preferred to

allow between their right wheels and the curb or

parapet of the bridge.

2. The tread width of the average car.

3. The distance of the left wheel to the right of

the center line for vehicles meeting on the tangent

section, which is equivalent to one-half the clear­

ance between the left wheels of vehicles when

meeting.

When Walker applied these values to a 22 foot wide

roadway section, he found that a bridge width of 30.6

feet was required.

Quimby (13) conducted a series of tests at a narrow

bridge on U. s. Highway 52, one mile east of Templeton,

Indiana, in 1947, to determine the effect of various

types of prevailing delineation deviceson the speed and

lateral placement patterns of passenger cars. Four types

of signing installations were considered, including

reflector button warning signs and striped panel boards

at the bridge; standard size reflectorized background

warning signs with enlarged red button clusters at the

1 1

bridge; and reflectorized background signs with the panels

at the bridge, and with the panels and a painted re­

flectorized center line through the bridge and extending

into the approach. Quimby found that the warning signs

tended to cause the driver to encroach upon the center

line, an undesirable condition. Presence of the re­

flector! zed center line, on the other hand, was a

desirable control that channelized the traffic and led

drivers through the final approach within the correct

lane.

In 1958, Shelby and Tutt (14) conducted a vehicle

speed and placement survey, one phase of which studied

two-lane bridges. When they applied Walker's formula

for required bridge width (12), Shelby and Tutt found

that variable number one, the distance freely moviJla

vehicles preferred to allow between their right wheels

and the bridge parapet or curb , varied according to the

bridge width. It was felt by Shelby and !utt that the

adequate bridge width would be the width that would

encourage a vehicle to remain in the same lateral

position on the bridge that it occupied on the roadway

prior to entering the bridge. It was concluded that the

average driver needs a bridge width of 40 feet in order

to cross the bridge with 11 ttle or no deviation in the

lateral pea! tion .from that assumed on the approach

roadway.

12

Other Studies

It is normal driver behavior to swerve away from any

object that the driver considers a hazard. In 1963,

Michaels and Lozar (15) conducted an investigation to

determine what perceptual and field factors cause lateral

displacement. !hey concluded that lateral placement is a

special case in the field of velocity perception.

Michaels and Lozar found 'that, relative to the observer,

the displacing ob3ect moves laterally across the retina

with a definable angular velocity. Drivers react to this

apparant velocity by determining when and how much they

should displace on the basis of the time and distance at

which that velocity increases sharply.

One phase of Hormann's study on driver character­

istics {16) was concerned with lateral placement. He

found that when there are no oncoming vehicles, high speed

drivers tend to travel closer to the pavement center line

than low speed drivers; and when there were oncoming

vehicles, high speed drivers were farther from the pave­

ment center l~e than low speed drivers.

Summaty of Review of Previous ResearCh

From the preceding review of previous research,

several important roadway conditions can be considered as

being critical for the proper positioning of a vehicle

13

within its lane. Some of the more important roadway

characteristics are: a twelve foot lane width for mixed

traffic with a large percentage of trucks; edge striping;

center line marking; and several shoulder conditions.

These articles prove the value of lateral placement

studies.

CHAPTER III

METHODOLOGY

Test Locations

1 4

The two test locations for phase one of the study

were two bridges on U. S. Highway 63 near Rolla, Missouri.

One of the two bridges was located five miles north of

Rolla, and the second bridge was located eleven miles

south of Rolla. The average daily traffic (A. D. T.) for

these two locations was approximately the same, with

values of 2,950 vehicles per day at location number one

and 3,380 vehicles per day at location number two.

Figures for the A. D. T. at these two test locations were

obtained from the Missouri State Highway Department.

Figure 1 A is a map showing the test locations :iin respect

to the Rolla area.

These two bridges are similar in several aspects.

Both locations have approach lane widths and bridge lane

widths of twelve feet. Both locations have alternating

black and white dashed center lines, and both locations

have a constant edge stripe of four inches in width to

mark the outer edge of the twelve foot lanes. According

to Taragin's articles (7, 8, 9) and the two articles on

edge striping (10, 11), these features are the optimum

design characteristics to consider for proper vehicle

placement within its own lane. The two bridges used in

I 44

FIGURE I A

MAP OF THE STUDY AREA

BRIDGE NUMBER TWO

BRIDGE NUMBER

ONE

SCALE : I"= 2 MILES

1 5

this phase of the study are reflectorized for night

visibility.

Figure 1 is a photograph of bridge number one,

located north of Rolla. This bridge has an asphaltic

concrete surface, and an offset of one and one-half feet

from the center of the white edge stripe to the left

edge of the bridge abutment. This is shown in detail in

Figure 3, a plan view of the bridge. There are no

guardrails at this location. Adjacent to the approach

lane is ~ five foot wide gravel shoulder. Figure 4 is a

one-half section view of bridge number one.

Figure 2 is a photograph of bridge number two.

This bridge has a portland cement concrete surface, with

an offset of tour and one-half feet from the center of

the white edge stripe to the left edge of the bridge

abutment curb. This is shown in detail in Figure 5, a

plan view of the bridge. This location has an eight

foot wide paved shoulder adjacent to the approach lane.

This paved shoulder is tapered from a point one hundred

feet from 'the bridge entrance up to the abutment. !he

outer edge of this paved shoulder is marked by a metal

guardrail thirty inches tall • Figure 6 is a one-half

section view of this bridge.

16

The test location for phase two of the investigation

is located on Phelps County Route P, southwest of Newburg,

Missouri. Figure 7 is a photograph of this bridge,

located 1. 7 •ilea from the ;Junction of Phelps County

Figure 1 Bridge Number One, Located Five Miles North of Rolla, Missouri, on U. s. Highway 63, Looking North.

Figure 2 Bridge Number Two, Located Eleven Miles South of Rolla, on u. s. Highway 63, Looking West.

17

~

b 2'- o• 100'- o• A- 2'- o"H

J

I

FIGURE 3

~ r

-. r

A

I t4" f- 4" EDGE STRIP I j:t-s•

_j [ I

I

12'-o"

PAVEMENT CENTER LINE

..J r

I +-

12'- 0"

4" EDGE STRIP I "t""~'-s• TI.-4"

I " SCALE:-: 1'- 0" 8

PLAN VIEW OF BRIDGE NUMBER ONE.

_,. (X)

1 ~

: CD I -~

0 I II

w

z 0 a:: w

m

:l! :::> z w

(!) 0 a:: m

LL 0 <

( I <(

z 0 .... (.) w

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)

LL. ...J <

( I I

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19

J~. o" 1- 36o'- o" A --=-----:-l~s·;-o~· "l =Fs" -

4" PIPE RAILING'\_ 6" OURB'\

4" PIPE RAILING

A.-

4" EDGE STRI~

.

PAVEMENT CENTER LINE I

4" EDGE STRIP II

6" CURB

SCALE:..!.: 1'-0 8

FIGURE 5 PLAN VIEW OF BRIDGE NUMBER TWO.

I 611 4-

1 12.'- o"

12'- 011

j_ 4'- 611

-=lr;s"

N 0

21

0 b

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11.1

~~-------------_.__.....___

a:: CD

22

Routes P and T. This teat location is shown in Figure

1A and is noted as bridge number three. ~ere are no

edge stripes or center line markings on either the bridge

or the approach lane at this location. The approach lane

is ten feet wide, and is not centered on the 26 foot wide

bridge. Figure 9 is a full section view of bridge number

three that shows the approaCh conditions in detail.

Adjacent to the approach lane is a four foot wide gravel

and grass shoulder whose outer edge is marked by a 27

inch high metal guardrail. The average daily traffic at

this location is approximately 130 vehicles per day.

This A. D. T. value was obtained from the Missouri State

Highway Department.

Field Procedure

Measurement of lateral placemen~ for phase one of

the study was made through the use of a narrow strip of

gray slow-drying enamel paint perpendicular to the

pavement center line at the entrance to the bridge. The

test strip was oae-hal! incn wide and covered eight feet

of the lane of interest and extended two feet into the

opposing lane of traffic to record readings made when a

vehicle entered to the left of the bridge center line.

After each vehicle passed over the test strip, the amount

of lateral placement was measured and recorded, and the

used portion of the test strip was re-painted. Figure B

Fi&ve l Bridge l(mrfber ~ree, Lo oa ted 1 • 7 Miles From the Junction of Phelps County Routes P and ~' on Route P, Looking South.

Illua1;rative Example of the V/ay Both fll.ases of

-j•or-

T 3'-2"

APPROACH LANE POSITION 9"f//j:j l_ v zz z z z z z z z z z z , z z z•

~ 1 '- 4"+- 2'- o" ..1· 20'- o'" 1. ~- o" f 1'-4'j .,. _______________ 28'- 8" -..

SCALE; .l. • 1'- 0" 8

FIGURE 9 SECTION VIEW OF BRIDGE NUMBER THREE.

N ~

is a photograph depicting the manner in which data was

collected for the investigation.

25

The bridge center line was used as a reference point

for each reading for phase one of the investigation, and

the amount of lateral displacement was the distance

between this reference point and the leftmost edge of the

left tire track located on the test strip. This distance

was measured through the use of a metal yardstick, with

readings made to the nearest inch.

The observed vehicles consisted of automobiles and

small open-bodied trucks. No Volkswagens or similar

vehicles with small tread widths were recorded. Due to

the test proceedure, observations were limited to situ­

ations when a single vehicle passed over the test strip.

A queue of vehicles would leave several tracks on the

strip, making accurate readings difficult as only the

tread track nearest ~o the center line could be measured.

If this practice were followed, with just the nearest of

several tracks being recorded, an element of bias would

enter into the study. There were no recordings used when

a vehicle in the opposing lane of traffic was within one­

quarter of a mile of the observed vehicle as this might

influence how a driver positions his vehicle within his

lane. Recordings were taken at the same time of day on

the same day of the week one weelc apart at both locations

to eliminate any bias that might enter due to these

conditions. Fifty recordings were made at each of the

26

two test locations in phase one.

The proceedure for phase two of the investigation

was similar to tlle proceedure utilized in phase one. As

there are no edge stripes or center lines at the test

location used in this phase of the study, measurements

were made from the left edge of the west abutment of the

bridge to the right edge of the right tire tread track

left on the painted test strip. Measurements were made

to the nearest inch in the field, and converted to the

nearest one-hundredth of a foot for computations. The

same metal yardstick used in phase one was also used in

phase two.

Fifty observations were made under the existing

bridge conditions, after which both bridge abutments were

painted with Silver White "-Alert" reflective liquid,

provided by the Cataphote Corporation, Jackson,

Mississippi. Fifty observations were made under this

reflectorized condition, and the reflective liquid was

then painted over with gray concrete enamel paint as

requested by the Missouri State Highway Department.

Observed vehicles in this phase of the study were

the same as in phase one; namely, automobiles and small

open-bodied motor trucks. The same stipulations applied

in regard to a queue of vehicles, or situations when

there was a vehicle in the opposing lane of traffic.

CHAPTER IV

RESULTS

Results of Phase One

27

Tables 1 and 2 show the recorded values of the

lateral displacement at test locations one and two,

respectively. The two negative numbers in Table 1 indi­

cate that two readings were recorded when the left edge

of the left tire was to the left of the bridge center

line, or, in other words, the vehicle was partially in

the opposing lane of traffic, an undesirable condition.

Two statistical tests were applied to the collected

data (17). A statistical "t" test was used to compare

the means of the two sets of data. It was found that at

the 99 percent Confidence Interval there was a signifi­

cant difference between the means of the two sets of

data. The 99 percent Confidence Interval means that

there is a one percent chance of a Type I error occuring;

that is, rejecting a hypothesis when it should be

accepted.

The other statistical test used was an "F" test

utilizing a one-way analysis of variance that includes

the simultaneous comparison of means and variances.

Table 3 is the analysis of variance table for phase one.

From this table, it can be determined that there is a

significant difference between the one and one-half foot

28

TABLE 1

FIELD DATA FOR BRIDGE NUMBER 1

Located five miles north of Rolla, Missouri, on

u. s. Highway 63.

Read ins Dis;elacement Reading Dis;elacement (inches) (inches)

1 • ) 24 26.) 19 2.) 21 27.) 23 3.) 25 28.) 0

4.) 10 29.) 8 5.) 2 30.) 36 6.) 13 31.) 15 7.) 12 32.) 12

a.> 31 33.) 28

9.) 0 34.) 26

10.) 42 35.) 2 11 • ) 30 36.) 12

1 2.) 38 37 .) 20

13.) 11 38.) 19

14.) 27 39.) 28

15.) 40 40.) 4

16.) 34 41.) 30

17.) 13 42.) 19

18.) -3 43.) 31

19.) 1 44.) 5

20.) 9 45.) 34

21.) 24 46.) 22

22.) -2 47.) 23

23.) 12 48.) 34

24.) 15 49.) 5

25.) 22 50.) 23

12

I I

10

9

8

Cl)

1&1 7 _, 2 ::1: 1&1 > 6

..... 0

5

3

2

-X = 18.6

0 ~~~~~~~-A~~~~~~~~~--+---­-5 0 !5 10 15 20 25 30 35 40 45 50

DISTANCE IN t NC HES FR ON LEFT EDGE 0 F LEFT

TIRE TO MIDPOINT OF BRIDGE GENTER LINE

FIGURE 10 HISTOGRAPH OF THE DATA

COLLECTED AT BRIDGE NUMBER ONE.

29

30

TABLE 2

FIELD DATA FOR BRIDGE NUMBER 2

Located eleven miles south of Rolla, Missouri, on

u. s. Highway 63.

Readint:!i Dis;Elacement Reading Dis;Elacement (inches) (inches)

1 • ) 19 26.) 44 2.) 25 27.) 38 3.) 44 28.) 21 4.) 26 29.) 40 5.) 43 30.) 38 6.) 28 31 • ) 44 7 .) 28 32.) 26

8.) 29 33.) 34 9.) 32 34.) 16

10.) 36 35.) 30

11 • ) 24 36.) 44

1 2.) 1 2 37.) 35

13 .. ) 37 38.) 31

14.) 43 39.) 8

1 5.) 28 40.) 34

16.) 38 41 • ) 31

17.) 61 42.) 20

18.) 40 43.) 42

19.) 68 44.) 46

20.) 40 45.) 34

21 • ) 24 46.) 33

22.) 56 47.) 37

23.) 16 48.) 47

24.) 43 49.) 44

25.) 25 50.) 48

U)

LLI ..J 0 -::t: ..... >

"" 0

a:: ..... ED 2 ':;)

z

31

12

I I

9

8

7

6

5

4

3

2

o~~~~~~~~~~~~~~~+---~~_.~~

5 10 15 20 25 30 35 40 45 50 55 60 65 70

DISTANCE IN INCHES FROM L£FT EDGE OF LEFT

TIRE TO MIDPOINT OF BRIDGE CENTER LINE

FIGURE II HISTOGR APH OF THE DATA

COLLECTED AT BRIDGE NUMBER TWO.

TABLE 3 ONE-WAY ANALYSIS OF VARIANCE TABLE FOR

PHASE ONE.

SOURCE OF DEGREES OF SUM OF MEAN F

VARIATION FREEDOM SQUARES SQUARE

AMONG OFFSETS I 6,416.01 6,416.01 44.96

WITHIN A BRIDGE 98 13,986.18 142.72

"SIGNIFICANT AT 99°/o CONFlDE~CE INTERVAL

I ..

~ 1\J

offset at bridge number one and the four and one-half

foot offset at bridge number two.

33

The results of the "t" test confirms that the means

of readings recorded at the two test locations were not

equal. The results of the "F" test confirms that there

is a significant difference between the offsets at the

two test locations.

A one-way analysis of variance was used for phase

one of the study due to the similarity between the two

test sites. Both the approach lane widths and the bridge

lane widths were a constant twelve feet at both loca­

tions, and both test sites had edge striping and center

lines. Readings were taken at approximately the same

time of day and on the same day of the week at both

locations. The type of bridge structure was the same at

both sites. The only difference in the two test lo­

cations was in the amount of lateral clearance or offset

between the edge of the traffic lane and the edge of the

bridge abutment or curb; with values of one and one-half

feet at bridge number one and four and one-half feet at

bridge number two.

Results of Phase Two

Tables 4 and 5 show the recorded values of the

lateral displacement at bridge number three before and

after the bridge abutments were painted with the re-

34

TABLE 4

FIELD DATA FOR BRIDGE NUMBER 3 ,BEFORE REFLECTORIZATION

Located 1.7 miles to the west of the junction of

Phelps County Routes P and T, on County Route P, near Newburg, Missouri.

Readini Dis]2lacement Reading Dis]2lacement

(feet) (feet)

1 • ) 9.92 26.) 9.67

2 •. ) 12.50 27.) 8.25

3.) 10.42 28.) 11 • 50

4.) 10 .. 25 29.) 12.92

5 .) 9.83 30.) 7.67

6 •. ) 9 .. 42 31 • ) 10.50

7 .) 13.83 32.) 12.83

8 •. ) 1.1 .. 17 33.) 9.08

9.) 10 .. 33 34.) 12 .. 42

10.) 6 .. 75 35.) 10.58

. 11 .) 11.33 ;6.) 7.17

1 2.) 9 .. 08 37 .. ) 11.75

1;.) 9.58 ;s.) 9.58

14.) 10.50 ;g.) 7.92

1 5.) 9.42 40.) 11.00

16.) 10.75 41.) 11.50

17.) 10.08 42.) 9.83

18.) 11 .. 50 43.) 9.67

19.) 10.75 44.) 10.58

20.) 10.00 45.) 10.75

21.) 10.42 46.) 10.58

22.) 6.00 47 .) 7.92

23.) 11 .17 48.) 9.67

24.) 11.75 49.) 9.83

25.) 10.33 50.) 10.33

rn t.al .J (.) -l: 1&.1 > ~ 0

c t.al CD s ::)

z

35

12

II X = 10.25

10

9

8

7

6

5

2

0~~~~~~~~~~~~~~~~44~~~~~1 9.0 10.0 II. 0 12.0 13.0 14.0 6.0 7.0 8.0

DISTANCE IN FEET FROM RIGHT EDGE OF RIGHT TIRE TO LEFT EDGE OF WEST ABUTMENT

FIGURE 12 HISTOGRAPH OF THE DATA

COLLECTED AT BRIDGE NUMBER THREE

BEFORE REFLECTOR IZATION.

36

TABLE 5

FIELD DATA FOR BRIDGE NUMBER 3, AFTER REFLECTORIZATION

Located 1.7 miles to the west of the junction of Phelps County Routes P and T, on County Route P, near Newburg, Missouri.

Read in~ DisElacemen t. Read in~ DisElacement (feet) (feet)

1 • ) 6 .. 83 26.) 9.58

2.) 11 .17 27.) 10.33

3.) 6 .. 08 28.) 8.67

4 .. ) 8.67 29.) 11 .25

5.) 10.25 30.) 6.67

6.) 11 •. 17 31 • ) 7.42

7.) 12.50 32.) 8.33

8.) 6.17 33.) 6 .. 23

9.) 6 .. 42 34.) 9.17

10.) 10.67 35.) 10.83

11 • ) 9 .. 75 36.) 8.42

1 2.) 7.42 37.) 6 .. 92

1 3.) 7.08 38.) 6.58

14.) 10.17 39.) 7.42

1 5.) 10.33 40.) 6.33

16.) 8.67 41 • ) 8.58

17.) 9.92 42.) 6.17

18.) 9.75 43.) 9.00

1 9.) 10.25 44.) 7.92

20.) 6.33 45.) 8 .. 75

21 • ) 6.42 46.) 6.83

22.) 7.42 47.) 8.33

23.) 8.08 48.) 9.25

24.) 10.67 49.) 10.17

25.) 6 •. 17 50.) 8.08

12

II

10

0 .., ..I ()

% 8 w >

Cl: w m 2 6 ;:::)

z

4

3

-X = 8.5

0~~~~+4~~~~~~~~~~~~~~--

11.0 12.0 13.0 6.0 7.0 8.0 9.0 10.0

DISTANCE IN FEET FROM RIGHT EDGE OF RIGHT TIRE TO LEFT EDGE OF WEST ABUTMENT

FIGURE 13 HISTOGRAPH OF THE DATA

COLLECTED AT BRIDGE NUMBER THREE

AFTER REFLECTORI ZATION.

37

flectiv~ ttqutQ, respectively. ~bis data was analyzed

using t4~ ~ame two statistical t~sta utilized in phase

one; tha,~ .:ts, the "t" test and the "P" test. The "t"

test wa~ v~ed to test the population means of the before

and aft~f ~etl~ctorization conditions. Using a 99

percent ~~~f~d~nce Inter~al, it was determined that the

means o~ ~4e ~o conditions were not equal.

Ta~}~ 6 }~ ~e analysis of ~ariance table for phase

two of 1;~~ iA"est:i.gation. Res'Ul ts o.t the "F" test

confirm ~~~t iib.el.'e :ts a significq,nt difference in the

positio:fi~~~ af th.e vehicles witb.in their lane due to the

reflect~fy~t~on of the brid~e abutments.

A ~p~,w~j an~lysis of ~ari~ce was used for phase

two of cAl 1~"estigation sin~e all o.t the bridge and

roadway ~~~d~1iion8 remained the same for both parts of

this ph~~~ o~ the st~dy, with tb.e e~ception of the

reflect~~t~~}on o! the brid~e abutments.

38

TABLE 6 ONE- WAY ANALYSIS OF VARIANCE TABLE FOR

PHASE TWO.

SOURCE OF DEGREES OF SUM OF MEAN F

VARIATION FREEDOM SQUARES SQUARE

* AMONG CONDITIONS I 71.35 71.35 2. 7.55

WITHIN THE BRIDGE 98 254.12 2.59

*SIGNIFICANT AT 99% CONFIDENCE INTERVAL

i

J

~ 1.0

CHAPTER V

DISCUSSION OF THE RESULTS

The results of phase one of this investigation

verified that there was a significant difference in the

results obtained at location number one, that had an

offset of one and one-half feet, when compared to the

r·esul ts obtained at location number two, with a four and

one-half foot offset. The average change was 16 inches,

which means that the drivers of the vehicles at location

number two were more centered in their lane.

40

Upon further study of the data, when applying an

average vehicle tread width of six feet as suggested by

Taragin (7), it was found that 22 of the 50 readings at

location number two were closer to the pavement edge than

to the bridge center line by amounts of from one inch to

as much as thirty-two inches. By comparison, at test

location number one, only three of the 50 vehicles were

closer to the pavement edge than to the bridge center

line, with a variance of from two to six inches. It is

hypothesized that 44 percent of the drivers at location

number two, with the four and one-half foot offset, were

little affected by the proximity of the bridge abutment.

Results of phase two verify that there was a sig­

nificant difference in the positioning of a vehicle within

its lane after reflectorization of the bridge abutments.

The average difference was a change of 1.75 feet, or 21

inches, which indicates that the drivers drove closer to

the bridge abutment after it was reflectorized, and

therefore were closer to being centered within their

lane.

41

It was interesting to note that before the bridge

abutments were painted with the reflectorizing liquid,

only six of the 50 vehicles, or 12 percent, were intirely

within their lane; that is, their left tire was to the

right of the true pavement center line. Of this 12

percent, one half were encroaching within four inches of

this true pavement center line. After reflectorization

of the bridge abutments, however, 22 of the 50 vehicles,

or 44 percent, were entirely within their lane, a

significant improvement. Out of this 44 percent, only

three vehicles were within siz inches of the true pave­

ment center line. It would seem, therefore, that the

reflectorizing of the bridge abutments greatly influenced

the positioning of a vehicle in its entrance to the

bridge.

CHAPTER VI

CONCLUSIONS AND RECOMMENDATION3

Conclusions

42

The following conclusions are drawn from the results

of phase one of this investigation:

1. By increasing the amount of lateral clearance

between the edge of the traffic lane to the

nearest point on a bridee abutment or curb from

one and one-half feet to four and one-half feet,

drivers of passenger vehicles encroach on the

center line less, and thereby position the

center of the vehicle closer to the center of

traffic lane.

2. With a lateral clearance of four and one-half

feet from the right edge of the traffic lane to

the nearest point on the bridge abutment or

curb, over 40 percent of the drivers of passen­

ger vehicles drive closer to the pavement edge

than to the bridge center line.

3. With a lateral clearance of one and one-half

feet from the ri&ht edge of the traffic lane to

the nearest point on the bridge abutment or

curb, over 90 percent of the drivers of passen­

~er vehicles drive closer to the bridge center 0

line than to the pavement edge.

43

The following conclusions are drawn from the results

of phase two of this investigation:

1. With the absence of any form of bridge

reflectorization or warning for night approaches

over 90 percent of the drivers of passenger

vehicles are either partially within the

opposing lane of traffic or are encroaching

within four inches of the bridge center line.

2. With the presence of a reflective liquid

painted on bridge abutments, over 40 percent of

the drivers of passenger vehicles keep their

vehicle entirely within its lane; that is, the

left tire of the vehicle does not cross the

bridge center line and into the opposing lane

of traffic.

Recommendations

The following recommendations are suggested as a

result of this investigation:

1. In a follow-up study of phase one, observations

could be taken at a point 200 feet before the

bridge entrance. These values could be compared

to the observations recorded for the same

vehicle as it entered the bridge to determine if

there was a shift in the vehicle path during the

approach to the bridge. Such a shift may or may

not be more obvious at a bridge with a narrow

offset.

44

2. In a study similar to phase two, a reflectori­

zed center line could be painted to include the

approach to the bridge as well as the bridge

itself. A reflectorized center line may or may

not be better than reflectorizing the bridge

abutments.

( 1 )

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(1 0)

( 11 )

45

LITERATURE CITED

f;Iolmes, E. H.; and Reymer, S. E. "New rl'echniq ues .J.n Traffic Behavior Studies.n P!lblic Roads, April 1940, U. S. Bureau of Public Roads.

Green, H. F. "Method of Recording Lateral Position of Vehicles." Proceedings, Yol. 26, 1946, Highway Research Board.

Taragin, A.; and Eckhardt, H. G. "Effect of Shoulders_on Speed and Lateral Position of Motor Vehicles. 11 Proceedings, Vol. 32, 1953, Highway Research Board.

Taragin, Asriel "Driver Behavior as Affected by Objects on Highway Shoulders." Public Roads, Yol. 28, No. 8, 1955. U. S. Bureau of Public ·Roads.

T"aragin, Asriel "Driver Behavior Related to Types and Widths of Shoulders on Two-Lane Roads." Public Roads, Yol.29, No. 9, 1957, u. s. Bureau of Public Roads.

Case, H. W.; Hulbert, S. F.; Mount, G. E.; and Brenner, R. "Effect of Roadside Structures on Lateral Placement of Motor Vehicles." Proceedings, Vol. 32, 1953, Highway Research Board.

Taragin, Asriel "Transverse Placement of Vehicles as Related to Cross Section Design. 11 Proc_~_edings, Vol. 23, 1943, Highway Research Board.

Taragin, Asriel ttEffect of Roadway Width on Vehicle Operations. n Public_ Roads, Vol. 24, No. 6, 1945. U. S. Bureau of Public_ Roaus.

Taragin, Asriel "The Effects on Driver 3ehavior of Center Lines on Two-Lane Roads." Proceedings, ·val. 27, 194 7, Highway Research Board. -

Thomas. I. L.; and Taylor, W. T. "Effect of Edge striping on Traffic Operations." Bulletin, No. 244, 1960, Highway Research Board.

Missouri State Highway Department "Some Effects of Pavement Edge Lines on Driver Behavior." Missouri Cooperative Research Program, Report 69-10, 1969.

( 1 2)

( 1 3)

(14)

(15)

(16)

(17)

Walker, W. :P. "Influence of Bridge Widths on T"ransverse :Position of Vehicles." Proceedings, Vol. 21, 1941, Highway Research Board.

Quimby, W. s. "Traffic Pat·t.erns at a Narrow Bridge" Proceedings, Vol. 27, 1947, Highway Research Board. -

46

Shelby, M.D.; and Tutt, P.R. "Vehicle Speed and Placement Survey." Bulletin, No. 170, 1958, Highway Research Boara.

Michaels, R. M.;and Lazar, L. W. "Perceptual and Field Factors Causing Lateral Displacement." Record, No. 25, 1963, Highway Research Board.

Normann, o. K. "Influence of Driver Characteristics on Passenger Car Operation. 11 :Proceedings, Vol. 24, 1944, Highway Research Board.

Griffiths, J. c. "Scientific Methods in Analysis of Sediments." McGraw-Hill Book Co., 1967, Chapters 16 and 18.

47

VITA

Warren Chip Woods was born on April 26, 1948, in

Kansas City, Missouri. He received his primary and

secondary education in Kansas City. He has received his

college education at the University of Missouri-Rolla,

receiving a Bachelor of Science degree in Civil

Engineering from the University of Missouri-Rolla in

December 1970. He has been enrolled in the Graduate

School of the University of Missouri-Rolla since January

1971 •