Yellow-flowered Vetch - Vicia grandiflora
A native of Europe, is it is found in fallow and cultivated fields, lawns, roadsides, and along railroads (this was photographed on the side of a road). Despite the name, the flowers typically only yellow when in bud or first open, quickly turning almost white or a pale lilac. The flowers can be solitary or grow in pairs or threes. It is considered "weedy" as many species of its genus.