Angry residents claim plans to triple the size of a school will cause a traffic nightmare and could even put students' lives at risk.
Proposals have been revealed to expand Ecclesall Infant School into a primary school to meet increased demand for pupil spaces.
The £4.9 million expansion would eventually see the school increase in size from 180 students to 630 over four years.
But residents who live across from the school claim High Storrs Road already gets clogged up with parents parking up to drop off and pick up their children and this will only get worse when the school increases in size.
They say there has been several accidents in recent years and fear it will only be a matter of time before there is another serious collision if the plans go ahead.
Company director and parent Julia Harrison, aged 47, whose daughter attends nearby Ecclesall Junior School, said: "The traffic is a nightmare. There are cars parked all over the place at peak times.
"There has been several accidents there in the last few years, including a girl who was hurt in a collision about a year ago.
"We are worried that there will be more accidents. It is hard for kids and and pedestrians to cross the road as they are having to duck out between parked cars."
She highlighted how High Storrs School is also on the same road, while the junior school is also just around the corner.
"It is just not feasible on that road, especially when the infant school will be three times the size. They need to rethink the plans and come up with an alternative."
Fellow resident Gillian Dudson added: "It takes me ten minutes to get out of my driveway at peak times. There is too much traffic as it is."
The expansion plans have been put forward after a council report highlighted an increase in birth rate and 'significant movement' of young families to the Ecclesall area meaning there is higher demand for school places.
The plans put forward include expanding the school by 90 places per year, starting September 2017, as well as widening the age range to take children up to age 11.
As part of the wider scheme to meet the increased demand for school places, nearby Clifford C of E Infant School would also be turned into a primary school to take in both infant and junior school pupils.
A letter sent to parents recently indicated that Ecclesall Junior School would eventually close and pupils would move to the new primary school.
The same letter indicated that school bosses hope to have the new structure in place by September 2018.
The expansion programme won the backing of Sheffield Council's cabinet last year.
A document on the school's website states there is a plan to "utilise and extend" existing buildings on the infant school site.
There is also a proposal to "create a new junior block which could be linked to the current Infant block."
The document added that there will be a traffic impact assessment undertaken and submitted as part of the planning application process, which will "assess the possibility of increase in traffic and may suggest mitigations that could be put in place."
It is estimated that the build will cost £4.9m and this will be paid for through the council's capital programme.
The school is believed to be consulting with parents over the plans ahead of submitting detailed planning applications.
A meeting to discuss the plans will take place at Clifford C of E Infant School on Wednesday, June 14, at 6.30pm.
We have asked Emma Hardy, executive head teacher at Ecclesall Infant School, and Sheffield Council for comment and are awaiting a response.