The boss of First Bus South West has sent an open letter to customers noting the "appalling disruption" passengers are facing across Bristol.
Managing director James Freeman blamed ongoing roadworks after the firm was blasted on social media for delays.
The worst affected routes were on the Bristol ring road, where passengers endured late and overcrowded buses.
A spokesman for the council said it was investing £160m in the road network to "reduce congestion and emissions".
Mr Freeman's letter began: "Here we are at the start of a new decade and no more than a week into it we are confronting appalling disruption to our lives as a result of traffic congestion, particularly in the northern fringe of the conurbation.
"While this affects many people, it particularly impacts people who have made the lifestyle choice to use public transport to travel, particularly to their work."
He listed some of the affected areas where buses were "gummed up in appalling delays" on the A4174 Ring Road - a 35-minute journey that was taking an hour and 35 minutes.
"Not only is that frustrating for those on board, arriving at work late, in all probability, but it also means that the buses weren't getting back to Emersons Green to operate their next trips," he said.
Mr Freeman acknowledged passengers getting stranded in some places including Hambrook was due to overcrowding.
He also highlighted problems on the M1 Metrobus route, saying: "...on Tuesday South Glos Council started long term road works at the Great Stoke roundabout on Bradley Stoke Way.
"The resulting congestion has delayed buses by up to 40 minutes on each journey at the key morning peak times."
A spokesman for South Gloucestershire Council said: "With major new housing and business development planned in the area we are investing £160 million over four years on a number of highway improvement schemes to reduce congestion and emissions, improve cycling and pedestrian routes and make sustainable transport a more attractive option."
He added that some lanes were only being closed at off-peak times and the council was monitoring the impact of roadworks with some scheduling changes already made.
The M1 service seems to be particularly bad. Frequent full buses and long waits at peak times. If buses are the way forward for Bristol they need to be more reliable.— Marcus Watts🏉🐾 (@watts_mf) January 13, 2020
@metrobusBristol update please on what’s happening with the M1 through Bradley Stoke this morning please? I am now late for work again....— Gina Dagger (@DaggerGina) January 13, 2020
Mr Freeman has offered a "heartfelt apology" to bus customers affected and called for "urgent action".