Bristol Airport park-and-ride 'may affect M5 junction'
More information is needed to assess if a proposed airport park-and-ride site could have a negative impact on a busy M5 junction, Highways England warned.
Mead Realisation wants to build the car park for 3,000 vehicles close to junction 21, near Weston-super-Mare.
But Highways England says figures provided did not allow an accurate assessment to be made on the "safe and efficient" operation of junction 21.
The firm says it would take thousands of cars off local roads.
However, Highways England says the impact on the strategic road network - made up of motorways, A-roads and trunk roads - cannot be accurately determined.
It has given Mead Realisation three months to address the issues raised, otherwise it will recommend refusal on the grounds of insufficient information.
It added it "strongly supported" the retention of the land for future improvement to the junction.
The airport wants to expand its own parking sites as part of measures to increase passenger numbers to 12 million by 2026.
Details of the expansion will be discussed by planners at North Somerset Council later this year.
Mead Realisation says using a five-hectare field next to the M5 would avoid encroaching on to the green belt and a "traffic headache" on inadequate rural roads around the site at Lulsgate.
"The park-and-ride would be open 24/7 and create 60 jobs," a spokesman said.
"It will take thousands of cars off the already busy local routes and replace them with between three and five quiet, eco-friendly buses an hour."