The 1.2 mile stretch of the A49 in Shropshire has been found to have had an average speed in 2022 of just 8.4mph.
That same stretch of road has also been named as the UK's most delayed as motorists lose 305 seconds (more than five minutes) per mile on average.
The research was analysed by financial platform, Forbes Advisor, who looked at the slowest, most delayed and worst maintained roads in England by using Department for Transport data to pinpoint where in the country's motorists are most likely to be held up for the longest time and move at the slowest average speeds.
They found that 1.2 mile stretch of the A49 northbound between the B4368 Craven Arms (north) and the A489 was Britain's slowest road where traffic crawls along at a snail's pace.
Motorists heading along that stretch of A49 are delayed for 40 seconds more than the UK's next worst stretch of road, a 1,500 metre piece of the A627(M) outside Rochdale, where traffic crawls at 10.1mph on average.
A stretch of the A30 in Surrey (eastbound) between the M25 and A308 which had an average speed of 10.6mph, was named the third worst stretch of road by Forbes.
The A49 runs north from Ross-on-Wye in Herefordshire via Hereford, Leominster, Ludlow, Shrewsbury and Whitchurch, then continues through central Cheshire to Warrington and Wigan.
Different stretches of the road in Shropshire make up no fewer than six of the slowest 10 stretches of road for average speeds, and five of the worst 10 for time lost to delays, according to Forbes' research.
But overall, it is not the worst highway in the UK when analysing roads in their entirety. That dubious honour goes to A2270 in East Sussex where speeds average just 13.7mph along the entire four-mile stretch of road that leads to Eastbourne.
However, the A49 in Shropshire is notorious in the county for delays and hold ups. It is also a stretch of road that sees regular accidents.
In August last year, a 25-year-old motorcyclist from Ludlow died after he was in a serious collision on the A49 near Craven Arms. At the time of the incident police said the biker had hit a signpost near the roundabout with Whitemeadow Close.
A month later on the same stretch of the A49, two people were taken to hospital after a collision between a car and a van . And in January this year, the now stretch of road had to be closed one evening when an articulated lorry carrying sheep hit a car.
Findings of the research by Forbes Advisor found highways in England and Wales need £14 billion worth of repairs and that there are 22,600 miles of road in 'poor' overall condition - almost the equivalent length of the equator.
Kevin Pratt, car insurance expert at the magazine-linked advisory firm, said: "Suffering delays when driving is routine these days, with many of us building in an allowance for getting stuck in traffic or generally making slow progress.
"Traffic apps are specifically designed to identify known problem areas so we can - hopefully - take evasive action.
"This situation is in some respects inevitable given that we now have over 30 million vehicles in the UK - the roads are simply at full capacity.
"But it is also the case that many delays are caused by roads being in poor condition and drivers responding accordingly - half of motorists say poor road conditions is the primary reason they feel unsafe when driving.
"It is vital that our roads infrastructure is properly maintained to help keep traffic running as smoothly and efficiently as possible.
"Collectively, drivers pay billions every year in excise duty and fuel tax, so it is only right they see money flowing in the other direction."