The increase in humanity would inevitably mean extended travel times for drivers using the congested Offington Corner roundabout at Worthing in particular, said a spokesman.
“The explosion in numbers is such that we might even have to think the unthinkable – advising the public to use the A259.”
Sussex Police had been trying to contact the United Nations for projections on how the growth would affect the south coast dual cariageway but had received no response, he claimed.
"We understand that the UN has its hands full preparing for massive inequalities between nations in housing, work and food but they must understand that we need to plan for possible tailbacks on the Holmbush slip road at Shoreham-by-Sea."
As world resources continued to dwindle and countries experienced mass exodus as a result of famine and war, police were advising people to leave longer to use the park and ride in Worthing town centre, he said.
“By the end of this century the world population is expected to be 10 billion. That gives us just 89 years to sort out that off-peak resurfacing work between between the B2233 Nyton Road junction and the A29 junction at Fontwell.
“We’re watching the UN’s projections very carefully and in case of a doomsday scenario we’ve got 200 cones at the ready.”
* The head of Worthing’s Shopmobility charity says he has been trying in vain to personally phone UN secretary general Ban Ki-Moon to gauge whether the town will now have enough scooters for the elderly.