(A) 
No vehicle may be driven upon any highway of this city at a speed which is greater than is reasonable and proper with regard to traffic conditions and the use of the highway, or which endangers the safety of any person or property. The fact that the speed of a vehicle does not exceed the applicable maximum speed limit does not relieve the driver from the duty to decrease speed when approaching and crossing an intersection, when approaching and going around a curve, when approaching a hillcrest, when traveling upon any narrow or winding roadway, or when a special hazard exists with respect to pedestrians or other traffic or by reason of weather or highway conditions. Speed must be decreased as may be necessary to avoid colliding with any person or vehicle on or entering the highway in compliance with legal requirements and the duty of all persons to use due care.
(B) 
No person may drive a vehicle upon any street at a speed which is greater than the applicable statutory maximum speed limit established by divisions (C) and (D) below, by § 71.002, or by a regulation or ordinance made under this chapter.
(C) 
Unless some other speed restriction is established under this chapter, the maximum speed limit in an urban district (as defined in § 70.01) for all vehicles is:
(1) 
Thirty miles per hour; and
(2) 
Fifteen miles per hour in an alley.
(D) 
Unless some other speed restriction is established under this chapter, the maximum speed limit in a non-urban district is 55 miles per hour.
(ILCS Ch. 625, Act 5, § 11-601)
(A) 
(1) 
For the purpose of this section, a SCHOOL DAY shall begin at 7:00 a.m. and shall conclude at 4:00 p.m.
(2) 
On a school day when school children are present and so close thereto that a potential hazard exists because of the close proximity of the motorized traffic, no person shall drive a motor vehicle at a speed in excess of 20 miles per hour while passing a school zone, or while traveling upon any public thoroughfare where children pass going to and from school.
(3) 
This section shall not be applicable unless appropriate signs are posted upon streets wherein the school zone is located. With regards to the special speed limit while passing schools, signs shall give proper due warning that a school zone is being approached, and shall indicate the school zone and the maximum speed limit in effect during school days when school children are present. Nothing in this chapter shall prohibit the use of electronic speed-detecting devices within 500 feet of signs within a special school speed zone indicating the zone, as defined in this section, nor shall evidence obtained thereby be inadmissible in any prosecution for speed, provided the use of the device shall apply only to the enforcement of the speed limit in the special school speed zone.
(B) 
Use of electronic surveillance. Nothing in this chapter shall prohibit the use of electronic speed-detecting devices within 500 feet of signs within a special school speed zone or a construction or maintenance zone indicating the zone, as defined in this section, nor shall evidence obtained thereby be inadmissible in any prosecution for speeding, provided the use of the device shall apply only to the enforcement of the speed limit in the special school speed zone or a construction or maintenance zone.
(C) 
(1) 
Definition. For the purpose of this section, a CONSTRUCTION OR MAINTENANCE ZONE is an area in which the Department, Toll Highway Authority, or a local agency has determined that the pre-existing established speed limit through a highway or construction or maintenance project is greater than is reasonable or safe with respect to the conditions expected to exist in the construction or maintenance zone and has posted a lower speed limit with a highway or construction or maintenance zone special speed limit sign.
(2) 
Design. Highway construction or maintenance zone special speed limit signs shall be of a design approved by the Department. The signs shall give proper due warning that a construction of maintenance zone is being approached and shall indicate the maximum speed limit in effect. The signs shall also state the amount of the minimum fine for a violation when workers are present.
(ILCS Ch. 625, Act 5, § 11-605(a) -(c))
No person shall drive or operate any motor vehicle on any street or highway in this city where the minimum allowable speed on that street or highway, as posted, is greater than the maximum attainable operating speed of the vehicle. Maximum attainable operating speed shall be determined by the manufacturer of the vehicle and clearly published in the manual of specifications and operation, or it shall be determined by applicable rule and regulation promulgated by the Secretary of State.
(ILCS Ch. 625, Act 5, § 11-611)
No person shall drive a motor vehicle at such a slow speed as to impede or block the normal and regular movement of traffic except when reduced speed is necessary for safe operation of his vehicle or in compliance with law.
(ILCS Ch. 625, Act 5, § 11-606(a))