Iowa Code Title VIII. Transportation [Chs. 306-330B] § 321.321. Entering through highways

The driver of a vehicle shall stop or yield as required by this chapter at the entrance to a through highway and shall yield the right-of-way to other vehicles which have entered the intersection from said through highway or which are approaching so closely on said through highway as to constitute a hazard, but said driver having so yielded may proceed cautiously and with due care enter said through highway.