Number : IRC3-0069

Study on the Securement of Smooth Traffic Flowon Roundabouts in Cold, Snowy Regions
ByMr. Tetsuya Ogami, Researcher, CERI, PWRI, Japan
Mr. Masatoshi Makino, Senior Researcher, CERI, PWRI, Japan
Mr. Masahiro Ishikawa, Researcher, CERI, PWRI, JapanMr. Yuji Yanagisawa, Team Leader, CERI, PWRI, Japan

1. Introduction
Roundabouts have been actively introduced in many countries due to the higher levels of safety, traffic flow andeconomic efficiency they offer compared to general intersections. Japan is no exception to this trend. Guideline
development and other steps are being taken in an effort to introduce roundabouts. In addition, demonstration data on
test roads are being collected.
collected However,However the introduction of roundabouts in Japan has so far been limited,
limited andmethods for roundabout winter management have not yet been developed.
In this context, the authors examined an efficient snow removal method for roundabouts by performing a wide range oftests on a simulated roundabout with the aim of enhancing road transportation safety in winter.

2. Cold, snowy regions in Japan
Approximately 60% of Japan’s land area is made up of cold, snowy regions, in which as many as 28
milliono peoppeople
e live.
e Thiss iss a ssituation
tuat o foundou d in few
e otothere pplaces
aces worldwide.
o d de The
e ccityty oof Sappo
Sapporoo in Hokkaido
o a do (Japa(Japan’ssnorthernmost island) is the only urban area in the world that has a population of over one million combined with annual
snowfall totaling as much as five meters.
Sidewalk sideAsahikawa
Sapporo Asahikawa Niigata

Sendai

SapporoKitami

SendaiHighest

36 2
36.2

36 0
36.0

39 1
39.1

36 8
36.8

Temperature
Lowest(˚C)

-23.9

-41.0

-13.0

-11.7

Annual average
Niigata

Tokyo

8.5

6.7

13.5

12.1

Total precipitation (mm)

1,128

1,074

1,776

1,242

Cumulative snowfall (cm)

496

647

165

70

Max. snow depth (cm)

98

90

30

13No. of snowy days

132

148

58

36.6

Roadway side

： Cold, snowy regions： Snowy regions (the max. snow depth in Feb. is at least 50 cm)： Cold regions (average temperature in Jan. is below freezing)Cold, snowy regions in Japan

Snow piled up between a sidewalk and roadway(Kitami Hokkaido)(Kitami,3. Study principles①For efficient snow removal at roundabouts
Vehicular swept paths for different types of snowplow were measured to investigate their suitability fora roundabout and allow the proposal of a snowplow selection method.

②For enhancement of roundabout safety in winterChanges in actual visibility and driver influence resulting from different snow pile locations andheights were surveyed to allow the proposal of appropriate snow locations andheights.

4. Vehicular swept path test
A vehicular swept path test was conducted to determine the effectiveness of each type of snowplow in removing snow(traveling) at roundabouts.

In the test, snowplows were driven on a simulated full-scale roundabout to obtain RTK-GNSS
measurement data. For measurement, a fixed station was set up at the test track and mobile stations were mounted
on top of the test vehicles. Based on the measurement results, vehicle locations and travel directions wereascertained. Continuous vehicular swept paths and the positions of the four corners of the travelingvehicles were also surveyed by superimposing them onto pre-registered map data (using road configurationsand vehicular external dimensions).

4.1 Test conditions
・Test vehicles: snow-removing truck, snow-removing motor grader, snow-removing wheel-type loader
・Travel patterns: loop, right turn, straight line, left turn・Travel speed: speed expected in snow removal operations, minimum speed
・Measurement and analysis interval: 1 sec.

S hSchematici diagramdiof the test snowplows

Snowplow/FeaturesSnow-removing truck(10-ton class)・Superior mobility and comfort
・Positioned mainly in suburbs

Overall length = 11,900mm

Snow-removing motor grader(4.0-m class)Central island
Truck apron

・Superior workability and ability toremove compacted snow
・Positioned mainly in urban areas

Overall length = 9,920mm

Snow-removing wheel-type loader(13-ton class)
Circulatory roadway

Traffic island

・Superior maneuverability
・Positioned usually for specificuses such as community roads
and intersections

Simulated roundabout configuration

Overall length = 7,500mm

Four corners of the vehicles
mobile stations(GNSS receiver)Featureseatu es oof typ
typicalca ssnowplowso po s

4.2 Test results
Snow-removing truck

Snow-removing motor grader

Snow-removing wheel-type loader(speed: 11.2 km/h)(speed: 7.5 km/h)(speed: 6.8 km/h)

On‐vehicle mobile station(GNSS receiver)

ＤＡ

Ｃ

Fixed station(GNSS receiver)

Installation of GNSS instruments
Ｂ

Example ： snow-removing wheel-type loader
Vehicle passage point （ In m）
Measurement
Front
Rear
Front
Rearpointright-side right-side left-side left-side
tiptiptiptipApprox. 8.5 m

Approx. 6.0 m

Approx. 4.0 m

Results of vehicular swept path test (Travel patterns : loop)

AB
CD

4.84
4.79
4.81
8
4.80

5.68
5.82
5.93
593
5.70

7.16
7.07
7.24
7.09

7.67
7.69
7.92
9
7.68

5. Proposal of a snowplow selection method
・The vehicular swept path test revealed that the snow-removing wheel-type loader was capable of traveling along theedge of the central island and the outer circumference of the circulatory roadway, which the snow-removing truck andsnow-removing motor grader could not do. Accordingly, the snow-removing wheel-type loader was deemed to be best
suited for the simulated roundabout (circulatory roadway outer diameter: 26 m; central island diameter: 8 m).
・On
On roundabouts with larger central island diameters,
diameters snow-removing trucks and snow-removing motor graders,
graders whichhave better mobility and workability than snow-removing wheel-type loaders, can be used.
・It is also necessary to adequately consider the conditions of roundabout approach roads and the types of snowplows
already positioned there.

The snowplow types to be used must be selected in consideration of field
conditions in addition to the results of vehicular swept path testing.

6. Visibility confirmation test
A test concerning the visibility of drivers and pedestrians at a roundabout in snowy conditions was conducted.

In the test, simulated snow piles and objects (moving vehicles and pedestrians) were positioned at thesimulated roundabout, and pictures were taken from the eye heights of drivers and pedestrians using digital
cameras to show how they saw each other. By comparing images with varying shooting conditions (objects, snowheights, etc.), changes in visibility were determined. The number of pixels in the visible area of the objects was alsocounted for quantitative assessment of the visible area.

6.1 Test conditions
・Objects : passenger cars, snow-removing motor graders,pedestrians (dummies)
・Simulated snow piles : at 7 locations(central island and entrance/exit)
・Simulated snow pile height : 0 m, 1.2 m, 1.5 m
・Camera: digital single-lens reflex (with fixed 50 mm lens)Simulatedsnowｃｂ
Circulatory roadway ： A － D ＝ Vehicles

Shooting condition(at eye height from snow-removing motor grader)

Entrance： １ － ３ ＝ Vehicles

Sidewalk： ａ － ｃ ＝ PedestriansａPositions of vehicles and other objects

6.2 Test results
・The results of the visibility test confirmed that actual visibility for a snow height of 1.5 m differedsignificantly from that for a height of 1.2 m.
・As a specific example, a survey was carried out in which a car was located at “Position C” on the circulatory roadway
and a pedestrian was located at “Position b” on the sidewalk to allow examination of vision from each point. The results
for a snow height of 1.5 m showed that only the head of the pedestrian (approx. 4% of the total body area) was visible
from the car, and only the top of the vehicle (approx. 19% of its total area) was visible from the pedestrian’s point ofview. In contrast,, when the snow was 1.2 m high,g , the entire vehicle ((100%)) was visible,, and the ppedestrian was visible
from the chest up (approx. 21%).
・The lower part of objects used in these tests (dummies and vehicles) tended to have a larger visible area. In somecases, it increased more than fivefold when the snow height decreased from 1.5 m to 1.2 m, quantitatively confirmingthat differences in visibility exceed differences in snow height.
１．５ｍ

Visual object

１．２ｍ

１００％ visible

Pedestrian “ｂ”
No snow

Shot fromApprox. １９％ visible

No. of pixels％

Snow height 1.2 m

Snow height 1.5 m

No. of pixels

No. of pixels％％

Snow-removing motor grader on circulatory roadway A

5,135

100%

1,838

35.8%

678

13.2%

Snow-removing motor grader on circulatory roadway B

12,102

100%

4,614

38.1%

244

15.0%

Snow-removing motor grader on circulatory roadway C

19,580

100%

9,271

47.3%

3,628

18.5%

Passenger car on circulatory roadway A

6,730

100%

501

7.4%

00.0%

Passenger car on circulatory roadway B

15,064

100%

3,470

23.0%

619

4.1%

Passenger car on circulatory roadway C

31,602

100%

6,698

21.2%

1,249

4.0%

Comparison of visible area (example)

Pedestrian “ｂ” Æ vehicle in the circulatory roadway “C”
１．５ｍ

Approx. ４％ visible

１．２ｍ

Approx. ２１％ visible

Vehicle in the circulatory roadway “C” Æ Pedestrian “ｂ”

CComparisonioff visibility
i ibilit variedi dbby diffdifferentt snow heights
h i ht7. Subjective assessment test
A subjective assessment test was conducted to determine the degree of hindrance caused by each snow pile todriving performance.

In the test, 17 subjects drove on the simulated roundabout where simulated snow piles were positioned,
and assessment was made using a questionnaire (with answers indicated on a scale of 1 to 7). The snowpiles were simulated by attaching white netting to survey poles.

7.1 Test conditions
・Simulated snow piles : at 7 locations(two different profiles for Traffic Island A )・Simulated snow pile heights : 1.2 m and 1.5 m
・No. of snow piles evaluated : 16
・Test vehicle : passenger car (Toyota Cardina)
・Travel route : Entrance→ Circulatory roadway (loop) → Exit

Simulated snow piles and Test vehicle

Ｑ ： Check the most appropriate severity of hindrance caused
by each snow pile when you were driving.
【First driving test】

Traffic Island A

Central island
Exit A

Exit A(adjacent approach road)
Entrance A

Traffic Island A’
Exit B

Name：

Central island

1.2m

1234567

Entrance A

1.2m

1234

56

7

Entrance B

1.2m

1234

567

Exit A

1.2m

1234

567

Exit B

1.2m

1234567

Traffic Island A

1.2m

1234

567

Traffic Island B

1.2m

123456

No hindrance

Entrance B Traffic Island B

7Hindran ce

Driving course and questionnaire of subjective assessment test

7.2 Test results
The results of the questionnaire answered on a scale of one toseven were standardized for each subject to give standard
values in order to facilitate comparison for each snow pile. A
subjective assessment score for each pile was found by
averaging all the subjects’ standard values.
In this case, higher
gscores mean a ggreater hindrance to driving
gperformance.
・Standard value (a) = (Individual assessment score– Average score) / Standard deviationn・Subjective assessment score = 1 / n Σ ａ ｊ
ｊ=1※Focus of attention : Pedestrians > Traveling vehicles※Snow height: 1.515m>1
1.22m※Snow location vs. snow height : Location > Height※Comparison of snow profile : influenced by the range of vision

Location of simulated
snowOn circulatory roadway
Central island
Traveling vehicles
Entrance A－
Entrance B－
Exit A－
Exit B－
Traffic Island A－
Traffic Island A’－
Traffic Island B－

Driving condition
Entering the roundabout
Traveling vehicles
Traveling vehicles
Pedestrians－－
Traveling vehicles
Traveling vehicles
Pedestrians

Exiting the roundabout－－－
Pedestrians
Traveling vehicles
Pedestrians
Pedestrians
Traveling vehicles

Objects to which attention is supposedly directed
1.50

１．２ｍ

１．５ｍ

1.00
0.50
0.00
‐0.50
‐1.00
‐1.50

Centralisland

Traffic
Island A

Traffic
Island A’

Traffic
Island B

Entrance A

Entrance B

Exit A

Exit B

Subjective assessment results

8. Proposal for snow pile locations and heights【Snow pile locations】
The results of the subjective
jassessment test indicated that it was best to pile removed snow on the “Central island”,“Entrance A”, “Exit B”.
However, the amount of snow piled at “Entrance A” may increase due to daily snow removal operations. In suchcases, snow will need to be piled at “Exit A” on the adjacent approach road to the roundabout. Thus, it is considered
optimal to pile snow removed from the roundabout at the “Central island” and “Exit B”.

【Snow pile heights】
The results of the subjective assessment test indicated that variations in subjective assessment scores (indicating thedegree of hindrance) were smaller for snow heights than those for snow pile locations. However, in the visibility
confirmation test, actual visibility varied significantly. Accordingly, a snow height of 1.2 m was considered preferable.

・Snow pile locations＝「Central island 」and 「Exit B」
・Snow pile heights＝「1.2 m」

are the most preferable

9. Summaryy【Results】
・This study enabled identification of a snowplow selection method and the proposal of snow pile locations and heights
in consideration of visibility.

【Future tasks】
・Tests involving vehicular swept paths on winter road surfaces will be conducted.
・Snow removal operation procedures and the costs associated with removing and piling snow will be examined.