Any process involved in the transition from the initiation to the elongation phases of transcription by a DNA-dependent RNA polymerase, generally including a conformational change from the initiation conformation to the elongation conformation. Promoter clearance often involves breaking contact with transcription factors involved only in the initiation phase and making contacts with elongation specific factors. [ http://www.ncbi.nlm.nih.gov/pubmed/15020047 http://www.ncbi.nlm.nih.gov/pubmed/18280161 ]