The number of buses and coaches using Mendip roads has fallen by more than a tenth over the last nine years, new figures show.
It comes as fewer buses were licensed across the UK at the end of last year than in any year since 2014.
The RAC said the fall is "disappointing", while the Campaign for Better Transport urged the Government to work with local authorities and bus operators to expand and improve bus services.
Department for Transport figures show 246 buses and coaches were licenced in Mendip at the end of 2023.
This was down from 265 the year before, and represented a fall of 13% since 2014, when there were 284.
Some 141,300 buses and coaches were registered across the UK at the end of last year, a 16% decline from nine years prior.
Rod Dennis, spokesperson for the RAC, said the fall is "disappointing at a time when so much public money is being spent on trying to make bus travel more attractive".
He added: "It’s little wonder then that so many people are as dependent on their cars as they are."
Silviya Barrett, director of policy and campaigns at the Campaign for Better Transport, said: "Schemes such as the £2 bus fare cap have helped to boost bus passenger numbers, but they are no substitute for long-term funding, and these figures show we still have a way to go to halt the vicious cycle of bus cuts.
"The Government must do more to support all local authorities so they can work with bus operators to run quality services and expand provision for the millions of people who rely on buses every day."
The Bus Users campaign group said losing bus services leaves people "without vital access to education, healthcare, employment, friends and family".
Chief executive Claire Walter said: "Funding for bus services is an investment that boosts local economies, reduces congestion and pollution, and improves health and wellbeing.
"We need ongoing, ring-fenced funding to protect these lifeline services for the future."