When diesel particulate filters (DPFs) were introduced with on-highway EPA 2007 emissions-compliant engines, one of the concerns was how often the DPFs would have to be cleaned of potentially clogging ash build-up. Fleets had to consider how and when to perform this maintenance task with little information upon which to base a decision. Recently, Chris Kemmer, research consultant for CK Marketing, surveyed a number of private and for-hire truckload (TL) and less-than-truckload (LTL), government and utility fleets on the subject of DPF maintenance. One fleet manager said they are just getting started in DPF operations. So far, there are no problems. Their main concerns are avoiding physical damage.