County roads in Iowa

Iowa's primary highway system
The state of Iowa is served by over 10,000 miles (16,000 km) of primary roads. The roads are spaced out evenly across the state, with clusters of primary roads near population centers.
System information
Notes:	Primary highways in Iowa are generally state-maintained.
Highway names
Interstates:	Interstate X (I-X)
US Highways:	U.S. Highway X (US X)
State:	Highway X (IA X or Iowa X)
System links
Iowa Primary Highway System Interstate U.S. State Secondary Scenic

The primary highway system makes up over 9,000 miles (14,000 km), a mere 8 percent of the U.S. state of Iowa's public road system. The Iowa Department of Transportation is responsible for the day-to-day maintenance of the primary highway system, which consists of Interstate Highways, United States Highways, and Iowa state highways. Currently, the longest primary highway is U.S. Route 30 at 332 miles (534 km). The shortest highway is Interstate 129 at 0.27 miles (0.43 km).

The 20th Century was a transformative time for vehicular transportation. In the early years of the century, roads were problematic at best – dusty dirt roads when dry and impassably muddy when wet. Over time, federal money was set aside and bonds were issued allowing the roads to be paved. The U.S. Highway and Interstate Highway Systems connected Iowa to the rest of the country and made national travel feasible. Periodically, new highway construction and changing driving habits have resulted in the obsolescence of local highways, to which the primary highway system has adapted. The former primary highways, turned over to counties and local jurisdictions, county highways, and farm-to-market roads make up the secondary highway system.

Early on, Iowa's registered routes were marked with hand-painted signs created by the group maintaining the highways. When the primary highway system was created, prisoners in Iowa's correctional system began making highway signs. Today, Iowa's highway markers are compliant with standards set forth in the Manual on Uniform Traffic Control Devices.

At the turn of the 20th century, roads in Iowa were suited for horse and buggy and ill-suited for automobiles. As more Iowans purchased automobiles, the Iowa legislature set up in 1904 a commission at Iowa State College in Ames to handle issues that arose concerning travel and safety. In 1904, less than 2 percent, or just over 1,000 miles (1,600 km) of public roads in Iowa had been improved with gravel or broken stone. The first task of the Iowa State Highway Commission, now the Iowa Department of Transportation, was to study Iowa's problematic roads. At the time, roads were merely dusty dirt trails when dry, and quagmires of mud when wet. By 1906, every county was maintaining its dirt road with drags. Designed by Missourian E. Ward King, road drags were a cost-effective way to smooth out dirt roads, costing as much as $3.00 ($80.00, adjusted for inflation) to build. In 1913, the Commission separated from Iowa State College and gained control over county and local transportation officials, who were responsible for road construction and maintenance. The Iowa Highway Commission did not gain jurisdiction over public roads until 1924.