otherwise posted, and 2 lane county roads have a speed limit of unless otherwise posted. In June 2015, the Arkansas Highway Commission authorized the Arkansas Highway and Transportation Department (AHTD) to raise the speed limit on undivided 4 and 5 lane roads from , and divided 4 lane roads from ; these changes affect of Arkansas highways. Furthermore, AHTD has established freeway default speed limits. Along rural freeways the limit is while suburban freeways are posted at . School zone speed limits apply only when children are present, or when a lighted beacon is on if one is provided and such speed limits are set at unless otherwise posted. It is fairly common however that schools serving only higher grade levels will not have a school speed limit in rural areas or where such school sits more than off of the highway or street. On March 16, 2017, the Arkansas House introduced a bill that would allow the state highway commission to increase speed limits up to in rural interstate freeways, upon completion of a "traffic and engineering investigation" and sets rural non-divided highway speed limits to . This bill became law on April 7, 2017, however no highways were immediately given a 75 mph limit. On April 8, 2019, Act 784 was approved which raises the speed limit to 75 mph / 70 mph for trucks weighing more than on all rural freeways effective July 1, 2020. The new law strikes the requirement for the Highway Commission to first conduct a traffic study before raising the limit; instead a study will be necessary for the Highway Commission to justify lowering the speed limit. As of August 5, 2020, new signs are up indicating the speed limit increase from 70 to 75 mph (70 mph for trucks) on I-40 west of Little Rock to the Oklahoma border. California Basic speed law California's "Basic Speed Law", part of the California Vehicle Code, defines the maximum speed at which a car may travel as a "reasonable and prudent" speed, given road conditions. The reasonable speed may be lower than the posted speed limit in conditions such as fog, heavy rain, ice, snow, gravel, sharp corners, blinding glare, darkness, crossing traffic, or when there is an obstructed view of orthogonal traffic—such as by road curvature, parked cars, vegetation, or snow banks—thus limiting the Assured Clear Distance Ahead (ACDA). Basic speed laws are statutized