In Iowa the maximum speed limit is posted on rural Interstate Highways that carry a 70 mph (113 km/h) speed limit and a 40 mph (64 km/h) minimum speed limit. Urban Interstate speed limits generally range from 55 to 65 mph (89 to 105 km/h), but may be lower in some areas. The majority of highways have a 55 mph (89 km/h) speed limit.
The Interstate 74 Bridge from Bettendorf to Moline, Illinois has a 50 mph (80 km/h) limit because the bridge is narrow and has no shoulders. Four-lane roads may have a 65 mph (105 km/h) limit. If the road is built to freeway standards, such as US 20 between I-35 and Dubuque, it may have a minimum speed limit, but otherwise four-lane roads carry no minimum limit so slow-moving farm vehicles may use the roadway.