Effects of road wetness Supresses suspension + direct emissions of salts and dust Up to almost 100 % Increases depot of PM Increases direct road wear Factor 2-3? Decreases tyre wear?

Factors influensing the street wetness Precipitation Rain/snow Amount Temperature Air/road Relative humidity Solar radiation Wind speed Wind causes the street to dry up faster Road salt and dust binding Salt bind moisture to the street Keeps the street wet for longer periods Traffic amount Vehicle speed Drainage Street slope Pavement texture

What can we learn from road surface wetness measurements? Areal variation of wetness on a street Rate of drying up on different spots of a street Variation between different streets Impact of – Street direction – Vehicle amount/speed/composition Compare with calculated road wetness Dynamics of wetness changes

Road surface wetness sensors Hornsgatan 5.10 m 3.50 m 6.60 m

Data available Hornsgatan, street canyon, ca veh/day – 3 sites, Period Sveavägen, street canyon, ca veh/day – 3 sites, Period Norrlandsgatan, street canyon, ca veh/day – 2 sites, Period Folkkungagatan,, street canyon, ca veh/day – 3 sites, Period

Example Hornsg Wetness + PM10 local contrib Delta PM10 Shows CRUCIAL to describe wetness correctly! Middle of road (1) less important! 12 3

Later in the year less difference in road wetness between sites

October 2009 March 2010 Long period of wet roads before

March 2007 Blue best to describe PM10 Feb 2008

Hornsgatan 29th and 30th Jan

Still wet in depot Hornsgatan 29th and 30th Jan

Sveavägen

Everything wetOnly driveway dry, Depot still wet Sveavägen 29th and 30th Jan 2011

Dry, but little traffic Dry daytime, with traffic Still wet Sveavägen 29th and 30th Jan 2011

E4/E20, 26th and 27th Jan 2011 Only dry in the wheeltracks. Still wet between lanes.

Street direction may be important Hornsgatan Sveavägen Norrlandsgatan

Comp of wetness on different streets Hornsgatan Sveavägen Feb 2009 March 2009

Nov 2009 Mar 2010