1.   No person shall drive a vehicle on any street within the corporate limits of the city at a speed greater or less than is reasonable or prudent under the conditions then existing (including, among other things, the condition of the vehicle, roadway, weather, visibility, amount of traffic, presence of pedestrians and any obstruction of view).
   2.   No person shall drive any vehicle upon a street at a speed greater than will permit a stop within the assured clear distance ahead.
   3.   No person shall drive any vehicle, except an authorized emergency vehicle (as provided in this chapter), at a speed greater than:
      a.   Twenty mph on any street adjacent to any school, or in any school zone, between 8:00 a.m. and 4:00 p.m. on days when school is in session, unless otherwise posted; and
      b.   Twenty-five mph on other streets and on streets adjacent to schools at other times than that specified immediately above, unless otherwise posted.