Essex Highways fears junctions in the towns will become constant traffic jams under the proposals by Basildon Council.
In Billericay the council proposes 1,400 homes to the west, 430 to the east, and 180 to the south on green belt land, while in Wickford 2,800 homes will be built in total over four sites.
The Essex Highways report predicts seven out of 10 junctions in Billericay, affected by development will fall into a code red category, meaning the junctions are above capacity during rush hour.
In Wickford, two out of five junctions affected would fall into code red.
Mike Andrews, of Outwood Common Road, Billericay, said: “Billericay is already stuffed up. There is no more space for shops or parking. We understand housing has to go somewhere, but why not land at Barleylands which has a road network.”
The fears over congestion on the roads comes as plans for a solar farm the size of 37 football pitches on land off Outwood Farm Road and Coxes Farm Road is also revealed.
Developer MS Power has been in talks with Basildon Council about the 8ft–high panels which would supply power to 2,500 homes.
Clive Aldous of Outwood Farm Road, Billericay, said: “We have been hit with a double- whammy and it’s very intimidating.
“I paid a premium to live here, but this will reduce the value of our property.
“The reason people live around Billericay is because of the green belt, it’s a lovely area.
But Billericay and Basildon will end up merging.
“We are not against these homes because they are behind where we live, it is because we don’t want to lose green belt right around Billericay.”
Tony Ball, leader of Basildon Council, said: “The council has spent the past year working with Essex Highways to identify where the capacity issues in the borough’s highway network and is continuing to work with them over the next few months to determine what highway solutions are feasible to address these issues and accommodate the level of growth and development locations in the current consultation document.
“This work is an ongoing exercise right up to the plan's submission to Government.”