The highway crosses the Canadian River into Seminole County north of Byng. Just after the bridge, US-377/SH-3E/99 intersect SH-39 and SH-56; this is their eastern and western termini respectively. Near Bowlegs, SH-59 joins the concurrency, splitting off again after . As the road enters Seminole, it has an interchange with US-270, where SH-3E splits off. SH-9 also is accessible by interchange in Seminole. US-377/SH-99 encounter another spur of the latter, SH-99A, in unincorporated Little. The routes then have an interchange at I-40, Exit 200.