Where traffic lanes have been marked on street pavements at places as traffic conditions require, it shall be unlawful for the operator of any vehicle to fail or refuse to keep the vehicle within the boundaries of any lane except when lawfully passing another vehicle or preparatory to making a lawful turning movement.
(Iowa Code §§ 372.13(4), 321.255) (1999 Code, § 61.05) Penalty, see § 10.99