richard jordan afternoon

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Presented by Name HereJob Title - Date

Some aspects of winter service in Europe

Presented by Richard JordanPrincipal Researcher – 24 March 2010

Agenda

Key drivers

Spread rates

De-icers

Effect of trafficking

Salt storage

1

2

3

4

5Water at road surface

Conclusions

COST 353

6

7

8National Winter Service Research Group9

Winter service - key drivers

Statutory Duty

Litigation/Liability

Road safety

Journey time reliability

Sustainability

Environmental impact

Value for money

Spread rates

Perception they have been higher in UK than in other European countries

Recent review of rates for precautionary salting

Need to understand reasons for variations from country to country

Why spread rates differ in different countries (1)

Legislation

Legal responsibilities

Policy

Attitudes to risk

Experience of congestion and accidents

Why spread rates differ in different countries (2)

Different winter weather

De-icer type/availability/cost

Treatment frequencies

Spreader performance

Road surface texture and air voids content

Operational experiences on different surfacing systems

Traffic levels

Driver behaviour in winter weather

Use of winter tyres

Climatic zones

Maritime- Temperature does not fluctuate greatly, relatively warm,

near 0C- Relatively little snow, high humidity

Cold Maritime- As maritime, but colder (more snow)

- Temperature changes, more wind

Central-European- Like maritime, but colder, fog

Mountain- Low temperatures, large daily range

- Much snow, strong winds

Continental- Often very cold, many frost days, long snowfall periods

- Relatively dry, relatively stable weather over longer periods

- Strong winds on some days

MARITIMEMARITIME

COLDCOLDMARITIMEMARITIME

NORTHERNNORTHERN

CENTRALCENTRALEUROPEANEUROPEAN

CONTINENTALCONTINENTAL

MEDITERRANEANMEDITERRANEAN

Spread rate comparisons (1)

Surface condition

Weather forecast

Road surface temp. (˚C)

Salt spread rate (g/m2)

WetFreezing and freezing fog

0 to -3 10 (dry)

-4 to -8 15 (dry)

MoistFreezing and freezing fog

0 to -3 10.3 (pre-wetted)

-4 to -8 15.5 (pre-wetted)

Wet Frost ≥ -210 (8) (dry)

6.2 (pre-wetted)

-2 to -520 (16) (dry)

9 (pre-wetted)

Moist Frost ≥ -210 (8) (dry)

6.2 (pre-wetted)

-2 to -520 (10) (dry)

6.9 (pre-wetted)Rates for national roads. For England, black figures are pre 2009/2010, red figures are from 2010.


Surface condition

Weather forecast



Wet 0 to -54.6 (pre-wetted)

4.4 (brine)

-5 to -107.4 (pre-wetted)

6.4 (brine)

Moist 0 to -53.4 (pre-wetted)

3.2 (brine)


5.3 (brine)


6.2 (pre-wetted)

-2 to -520 (16) (dry)

9 (pre-wetted)


6.2 (pre-wetted)

-2 to -520 (10) (dry)

6.9 (pre-wetted)


Surface condition

Weather forecast



Wet 2 to -5 15.4 (pre-wetted)

-5 to -10 18.9 (pre-wetted)

Moist 2 to -58.7 (pre-wetted)

3.5 (brine)


4.7 (brine)


6.2 (pre-wetted)

-2 to -520 (16) (dry)

9 (pre-wetted)


6.2 (pre-wetted)

-2 to -520 (10) (dry)

6.9 (pre-wetted)


Surface condition

Weather forecast



WetFreezing wet

road> -3

9.3 (pre-wetted)7.7 (brine)

< -314 (pre-wetted)

10.3 (brine)

Moist Rime/ice > -36.2 (pre-wetted)

5.2 (brine)

< -39.3 (pre-wetted)

7.7 (brine)


6.2 (pre-wetted)

-2 to -520 (16) (dry)

9 (pre-wetted)


6.2 (pre-wetted)

-2 to -520 (10) (dry)

6.9 (pre-wetted)

De-icers (1)

Sodium chloride normally used

Much dry salting in England

Pre-wetted salting on HA network and some local roads

Treated salting on some English roads

Much pre-wetted salting in Europe

Brine used in some countries and for all treatments in Funen, Denmark

Some abrasives and salt/abrasive mixes used in Europe

De-icers (2)

Sodium chloride- Effective temperature -8˚C

- Eutectic temperature -21˚C

Calcium and magnesium chloride brine used for pre-wetted salting at low temperatures

Calcium chloride eutectic temperature -55˚C

Magnesium chloride eutectic temperature -33.5˚C

De-icers (3)

Solid de-icers must dissolve to be effective by absorbing moisture:- From Road surface

- From Atmosphere if relative humidity > 80%

- Added during spreading (pre-wetting)

Dissolution assisted by trafficking- Fines particles dissolve first but are easily dispersed by trafficking

when dry salting

- Without traffic up to 50% may not be dissolved after 5 hours

Pre-wetted salt

Dry salt:Brine 70:30 by weight

Brine concentration: 23%

De-icer grading

6.3mm – most popular in UK

10mm – large particles can bounce so difficult to limit wastage

5mm or less used in parts of Europe – dissolves more rapidly, costs more, more consistent distribution?

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14 16 18

Salt

(g/m

2)

Distance across carriageway (m)

3mm

6.3mm

HS Lane 1 Lane 2 Lane 3

Salting losses due to trafficking (1)

Sweden – pre-wetted salt:

- 53 – 64% for 5000 passenger car equivalents

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Accumulated Traffic (No. of Thousand Private Car Equivalents)

Salt

loss (

%)

Klockrike Vimmerby


Denmark – pre-wetted salt:- 46/62% after 5/10 hours of low traffic

- 60/75% after 5/10 hours of high traffic

UK – pre-wetted salt:- 61% after 11,400 vehicles (20 hours)

- 62% after 3,100 vehicle (20 hours)

- 49/54/68% after 6,400/13,200/31,200 vehicles

(12/ 24 /48 hours)

UK – pre-wetted salt, trafficking immediately after spreading:- 56 to 68% after 900 vehicles (2 hours)

- 80 to 85% after 16,000 vehicles (25 hours)


Denmark (after 2 hours)- 35 to 40% - pre-wetted salt

- 10 to 15% - brine

Brine spreading (1)

Isomex spreading

Brine spreading (2)

Advantages: - Effective in low humidity conditions, including treatments at low temperatures

- Suitable for low dosage treatments for marginal nights

- Fast response on the road

- More accurate spreading and less wastage than solid de-icers

- Less loss due to trafficking so less salt required for some treatments

Disadvantages:- Passing vehicles may deflect the spray away from the target area

- Not well suited to heavy de-icing operations, and not recommended for snow, sleet or freezing rain treatments

- Requires vehicles equipped to spread brine

- Requires either brine production or brine storage facilities

Salt storage

UK- Barns

- Covered stockpiles

- Uncovered stockpiles

Silos used in parts of Europe

Salt storage requirements in some countries

HA guidance refers to 50 to 100% increase in spread rates for salt stored in open

Water at road surface (from Livet, 1998)

TrafficWater film thickness when surface is moist (mm)

Hot rolled asphaltNegatively textured

thin surfacing

Low 0.20 0.50 - 0.80

Medium 0.10 0.25 - 0.40

High 0.05 0.125 - 0.20

Traffic Water film thickness when frosty (mm)

Low 0.02 – 0.05mm

Surface state definitions (from Raukola et al, 1993)

DefinitionWater (g/m2)

Water film thickness

(mm)Description

Little moist 5 – 20 0.005 – 0.02Detectably dark road

surface

Moist 20 – 50 0.02 – 0.05 Clearly dark road surface

Wet 50 – 200 0.05 – 0.20 Spray phenomenon starts

Very wet 200 – 400 0.20 – 0.40Small drops of water in

the air

Flowing >400 >0.40Flow according to gradient, splash

Change in water film thickness after rainfall

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 10 20 30 40 50 60

Wate

r th

ickness (

mm

)

Time (mins)

Little Moist

Moist

Wet

DANGEROUSLY SLIPPERY ICE!

Loss of friction if ice

Effect of surfacing

Hot rolled asphalt- De-icer and water tend to remain on surface- Fairly rapid drainage

Porous asphalt- Cools quicker and gets colder than dense surfacing- De-icer enters voids- Requires higher spread rates and later treatments- Rapid drainage when voids not blocked

Other negatively textured surfacing- De-icer gets trapped in voids- Requires later treatments than dense surfacing- Surfacing becomes charged with de-icer over time- Needs trafficking and sufficient moisture to bring trapped de-icer (in solution) to

surface- Stays wetter for longer than dense surfacing

Conclusions on spread rates

Potential to reduce salt usage increases with:- Consistency of salt (moisture content, grading, purity)

- Uniformity of initial salt distribution (spreader settings)

- Rate of dissolution (time salt is in solution and not solid)

- Brine, pre-wetted salt, treated salt

- Lower maximum particle size (dependent on effects of wind)

Guidance is required for treatments in low temperatures- Calcium chloride, magnesium chloride

Need to determine water film thicknesses on local roads

Need to review spread rates for reactive treatments

Need to monitor effect of spread rate reductions

Improvement areas identified in COST 353: Winter service strategies for increased European road safety (1)

Road Weather Information Systems- Sensors

- Forecasting

Spreading technology- Higher speed

- Increased uniformity

- Quality control

Surface condition assessment- Friction

- Dry, moist, wet, ice, snow

Data management system- Car and vehicle information systems for collecting data

Improvement areas identified in COST 353: Winter service strategies for increased European road safety (2)

Management systems- Road Weather Information System

- Administrative Information System

- Call-out System

- Intelligent Equipment

- Link to Traffic Management

- Documentation and Follow-up

Road user information- Variable message signs

Safety measures- Road user education

- Winter driving test

Research topics identified in COST 353: Winter service strategies for increased European road safety

Monitoring road surface condition

De-icing materials and their effects- Temperatures below -10˚C

Winter service training and guidelines

Effect of weather on drivers, traffic flow and congestion

Intelligent transport systems

National Winter Service Research Group

Membership- Local authorities

- Service providers

- Industry

Developing Best Practice Guidance drawing on experience of membership and recent research

Thank you

Some aspects of winter service in Europe

Snow Summit 2010

Presented by Richard JordanPrincipal Researcher – 24 March 2010

Tel: 01344 770828Email: [email protected]

richard jordan afternoon

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