1ABSTRACTSwitzerland is enforcing the use of particulate traps for offroad applications like construction as well as for occupational health applications like tunneling. This decision is based on the results of the VERT-project (1994-1999), which included basic aerosol research, bench screening and field testing of promising solutions as well as the development of implementation tools like trap specification, certification scheems and field control measures.On the other hand there is no corresponding regulation for city-buses yet although PM 10 is about 2× above limit in most Swiss cities. Public pressure however is growing and city transport authorities have reacted by retrofitting Diesel city-buses instead of waiting for cleaner engine technology or CNG-conversions. The favored trap system with about 200 retrofits so far is the CRT. This system has successfully passed VERT-certification procedure revealing excellent filtration efficiency (> 99 %) even for ultrafine particles 20-200 nm, low back pressure (< 140 mbar) and continuous regeneration under most operating condition. NO2-slip seems relatively high which may be critical for use indoors - city bus application however seems ideal and is supported by a Swiss BUWAL field test campaign.