Improvements to the junction between the M4 and M5 in Bristol will still go ahead it was announced in the government Spending Review.
The hard shoulder will be opened up to traffic and variable speed limits introduced in the north of the city as part of works due to start this year.
But policing and council services in Bristol will be affected by the cuts.
Avon and Somerset Police said it was too early to speculate on the effect the review would have on the force.
The Spending Review was screened live in Bristol's Millennium Square, but few turned out to watch it.
The funding guarantee was given by Chancellor George Osborne as he announced more than £10bn for maintenance and investment in new high value road, regional and local transport schemes.
The so-called managed motorways project affects junctions 19 to 20 of the M4 and junctions 15 to 17 on the M5.
By 2012 the hard shoulders will be opened as lanes at peak times.
But Mr Osborne also announced funding cuts of 4% a year for police forces.
Avon and Somerset's Chief Constable Colin Port said: "A great deal of planning has been undertaken in the last five months to review a number of options that would help us meet different levels of cuts in our budget.
"Inevitably there will be some changes but until we have more detail I will not speculate."
Kevin Phillips, chairman of Avon and Somerset Police Federation, said he thought the cuts would ultimately lead to job losses.
"Avon and Somerset are working very hard to maintain front line police officers, but I think year on year this will be increasingly harder and eventually I think we will lose numbers," he said.
A spokesman for the Conservative-led North Somerset Council said they were looking at ways to save up to an extra £30m over the next four years to cope with their own funding cuts from government.
"As well as significant reductions in expenditure we will also be looking at different ways of delivering our services," the spokesman said.
"We acknowledge that as funding is reduced our workforce will also have to shrink."