C.R.S. § 13-6-503

At any hearing on a class A or class B traffic infraction or civil infraction, the officer who issued the citation or penalty assessment notice shall offer evidence of the facts concerning the alleged infraction either in person or by affidavit, as such affidavit may be established by rules adopted by the supreme court pursuant to section 13-6-501 (9). If the officer appears personally, the magistrate and the cited person may then examine the officer. The cited party has the right to call the officer by subpoena as in the case of other civil matters.