A new road link to the A12 will solve traffic congestion caused by plans for thousands of new homes.
But there is no guarantee it will be built.
Chelmsford and Braintree councils are worried plans for 2,610 homes in north Heybridge and south Maldon will lead to congestion on the A414 through Danbury and the B1019/B1137 junction in Hatfield Peverel.
Traffic lights at Eves Corner in Danbury are planned to help traffic on the A414.
A new junction connecting the B1019 to the A12 would help solve the issues in Hatfield Peverel, but Maldon District Council said the "significant costs" mean it is currently unaffordable.
Instead, the councils will try to lobby for funding.