(1) No person shall drive a vehicle at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing. Consistent with the foregoing, every person shall drive at a safe and appropriate speed when approaching and crossing an intersection or railroad grade crossing, when approaching and going around a curve, when approaching a hillcrest, when traveling upon any narrow or winding highway, and when special hazards exist with respect to pedestrians or other traffic or by reason of weather or highway conditions.
(2) (a)  Where no special hazard or condition exists that requires lower speed for compliance with subsection (1) of this section, the limits as hereinafter authorized shall be maximum lawful speeds, and no person shall drive a vehicle at a speed in excess of the maximum limits:
(i)   Thirty-five (35) miles per hour in any residential, business or urban district, unless otherwise posted in accordance with section 49-207(2) or (3), Idaho Code;
(ii)  Seventy-five (75) miles per hour on interstate highways, unless otherwise posted in accordance with section 49-201(4), Idaho Code, and provided that this speed may be increased to eighty (80) miles per hour if the department completes an engineering and traffic study on the interstate highway and concludes that the increase is in the public interest and the transportation board concurs with such conclusion;
(iii) Sixty-five (65) miles per hour on state highways, unless otherwise posted in accordance with section 49-201(4), Idaho Code, and provided that this speed may be increased to seventy (70) miles per hour if the department completes an engineering and traffic study on the state highway and concludes that the increase is in the public interest and the transportation board concurs with such conclusion;
(iv)  Fifty-five (55) miles per hour in other locations, unless otherwise posted, up to a maximum of seventy (70) miles per hour.
(b)  Subject to all other applicable motor vehicles laws, a driver of a passenger car, motorcycle or pickup truck, not towing any other vehicle, may exceed the posted speed limit by up to fifteen (15) miles per hour while passing another vehicle traveling at less than the posted speed limit, in order to safely pass the vehicle. The overtaking vehicle shall return to the right-hand lane and reduce speed to the posted speed limit as soon as practicable. This paragraph shall be applicable only to passing on the left upon roadways divided into two (2) lanes providing only one (1) lane of traffic in each direction and where the posted speed limit is fifty-five (55) miles per hour or greater. This paragraph shall not be applicable in construction zones. For purposes of basic rule violations and penalties imposed pursuant to this section and Idaho infraction rule 9, the fifteen (15) mile per hour allowance in passing situations provided in this paragraph shall be deemed to be the maximum speed limit from which fines are determined.
(3)  For vehicles with five (5) or more axles operating at a gross weight of more than twenty-six thousand (26,000) pounds the maximum lawful speed limit on interstate highways in nonurban areas shall not exceed ten (10) miles per hour less for vehicles with less than five (5) axles and operating at a gross weight of twenty-six thousand (26,000) pounds or less, and in urban areas the maximum lawful speed limit on interstate highways for such vehicles shall not exceed sixty-five (65) miles per hour.