A retro-fit system for buses and heavy duty trucks is presented, along with the mathematical modelling of soot (particulate matter or PM) combustion. In spite of the fact that the use of ceramic traps has lost popularity in the U.S. during the last few years, mainly due to the severe problems encountered during regeneration, a new approach to Diesel1* emissions control, is presented. Main objective is to attain the emissions levels set forth by the EPA for 1998, both on PM and NOx emissions. The very high levels of temperature required for thermal regeneration and elaborate controls, have almost eliminated the preference for ceramic filters. However, a new approach is presented by using catalyzed filters which considerably reduce the high temperature requirements. Along with the mathematical modelling a new hardware is presented, which is capable of performing filtering, regeneration, and operation with somewhat simpler and more economical controls. Improvements in the design of combustion chambers, higher injection pressures, better fuels and lubricants, etc., have made possible to re-think the concept of mechanical filtration of Diesel Particulate Matter (DPM).The development of the system has been partially sponsored by the Mexico City Goverment in an attempt to reduce the air pollution within the overloaded atmosphere of the large Mexico City Metropolitan Area (MCMA). Reported results are of the public domain.