The opening of Bristol's Metrobus scheme has been delayed again, with two of three main routes now not expected to start running until spring 2018.
The £230m transport system was due to begin operating in the city by the end of this year.
But work on the ticketing and information system is "taking time to get right," according to Metrobus.
Bristol City Council said it was "disappointed" the "hugely complex" project was delayed again.
Before boarding passengers on the MetroBus network will need to buy tickets online, in shops, using a mobile app or at iPoints, located at bus stops, which will also provide real-time journey information.
Testing of these iPoints are to blame for the latest setback. The Ashton Vale to Temple Meads and Cribbs Causeway to the city centre routes are now unlikely to open before Easter.
The third route, the South Bristol link, will open "as soon as possible" afterwards.
"The iPoints have to work first time, every time," a Metrobus spokesperson said.
"It's taking time to get right, we are making progress, and will not start services until we are 100 per cent confident."
The head of transport at Bristol City Council, Peter Mann, attempted to put a brave face on the latest setback.
"We're disappointed. We would have liked services up and running by now as we had originally planned," he said.
"But it is a hugely complex challenge and the team are running flat out so that we can start services in the new year."
Dogged by delays
The MetroBus system has been dogged by delays and rising bills.
In August it emerged the cost of building the network had gone up by almost 5% in a year to £230m, from initial estimates of £190m in 2015.
Transport campaigner David Redgewell from the group Bus Users UK said the system needed to be "launched properly".
"The last thing we want is buses running past half-built bus stops," he said.