It was formerly part of the A50 trunk road that ran from Bedfordshire to Lancashire.
For most of its length it is known as the Welford Road, except for small stretches near Welford where it is known as High Street and Northampton Road, and a section near Wigston Magna where it is known as Bull Head Street.
As its course is broadly parallel and near to the M1 motorway, it's very much lacking in modern features such as bypasses, which is why it was classified downwards when the A14 road, which it crosses at Junction 1, was built as a link between the M1/M6 junction and the East Coast ports.
City of Leicester Leicestershire Northamptonshire It terminates at a junction with the A508 in the Northampton suburb of Kingsthorpe.
Media related to A5199 road (England) at Wikimedia Commons