Illinois Axle Weight Limits

Maximum Legal Weight Allowed

Two consecutive sets of tandems may carry 34,000 pounds each providing the overall distance between the first and last axles of such consecutive sets of tandems is 36 feet or more.

Maximum legal weight for vehicles on all highways based on Federal Bridge Formula. (see table in DOC 2)

Practical Maximum Weights with a Permit

• 6 or more-axle tractor semitrailer combination 120,000 pounds gross; 48,000 pounds on drive tandem; 60,000 pounds on semitrailer tandem.
• 5-axle tractor semitrailer combination 100,000 pounds gross; maximum of 48,000 pounds on either tandem.
• 4-or-more-axle vehicle (axle spacing 23 feet or more): up to and including 76,000 pounds gross; maximum of 44,000 pounds on one tandem and 44,000 pounds on the other.
• 3-or-more-axle vehicle (axle spacing 18 feet or more): maximum 68,000 pounds gross; 20,000 pounds on one axle and 48,000 pounds on the tandem.
• 2-axle vehicle: maximum 48,000 pounds, neither axle exceeds 25,000 pounds.

Cook County Expressways – Movement of loads exceeding 12’ in width, 13’ 6” in height, or 120,000 pounds or the own powered equivalent are prohibited on the expressways in Cook County except;

• Int80 from Int57 east to the Indiana line, including portions of toll road Int294 and Int94
• Int55 south of exit 277
• Int57 south of US 6 (159th St.)
• Int290 north of toll road Int294

Own powered equivalents are: 4 or more axle vehicle up to 80,000 pounds gross; maximum 48,000 pounds on a tandem and 25,000 pounds per axle: or a 3 or more axle vehicle up to 68,000 pounds gross; maximum 48,000 pounds on a tandem and 25,000 pounds per axle: or a 2 axle vehicle up to 48,000 pounds with no axle exceeding 25,000 pounds

Source of information:
DOC 1 http://www.idot.illinois.gov/assets/uploads/files/idot-forms/oper/oper%20753.pdf 
DOC 2 http://www.idot.illinois.gov/Assets/uploads/files/Doing-Business/Manuals-Guides-&-Handbooks/Highways/Permits/Oversize%20and%20Overweight%20Permit%20Movements%20on%20State%20Highways%202015.pdf