Drivers reported some tailbacks after the vehicle came to a stop in the middle of the road near to The Balmoral.
Lothian’s fleet of 42 Falkirk-built 100-seat double deckers became the biggest bus in the UK when they started running in January.
“There’s a new longer bus broken down on Princes Street outside Balmoral - tailbacks and horns,” said one road user.
But he added: “It’s not actually too bad. Buses getting backed up on North Bridge but it clears quickly.”
The new buses see travellers alighting through middle doors for the first time in a decade to speed up services
They accommodate a total of 131 passengers, including those standing - half as many again as the older double deckers.
Each bus is 45ft (13.4m) long - four-foot longer than the existing fleet.
Other features on the six-wheelers include high-back seats to give passengers more personal space.
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