The vans were stopped and stolen on the M11 and M25 by fake officers in an unmarked car using blue lights.
Essex Police advised motorists they would only use unmarked car to pull over drivers in an emergency.
They now say the risk to motorists is low. Officers will return to using unmarked cars, which may stop vehicles.
The thieves, dressed in police uniforms and, in one case, carrying a handgun, drove a silver Ford Mondeo equipped with blue flashing lights and targeted van drivers.
DCI Stuart Smith of the Kent and Essex Serious Crime Directorate said: "My team of detectives have reviewed the circumstances of both incidents and alongside the intelligence have concluded the risk to motorists in cars is low.
"That does not mean that the only risk is to van drivers, but the only vehicles which have so far been stolen are vans."
His advice to van drivers is to "remain alert and vigilant and try and establish whether unmarked vehicles are genuine with our control room whilst remaining compliant with the police vehicle".
Ch Insp Nick Lee, head of roads policing, added: "The law states that you cannot use your mobile phone whilst driving, however, we have discretion we can apply and if someone is in genuine fear of their life we would take a sensible approach in those circumstances."
Essex Police issued the new guidance because there had been "no further reports of vehicle robberies in the county".
Drivers warned not to stop for unmarked police cars after two van robberies have now been told they should pull over.