 The third level contains ramps connecting northbound US 101 to northbound I-280 and southbound US 101 to northbound I-680, and the fourth level is a ramp connecting southbound I-680 to southbound US 101.This ramp is a site of major traffic, as there are only two lanes of the ramp from southbound I-680 to southbound US 101.The fourth-level ramp connects the third level ramp as they enter US 101, while the third-level ramp heading to northbound I-680 connects a ramp from northbound US 101 to northbound I-680.