A hunt for a refrigerated lorry on the A14 and M11 this week began after three men called the police to say they were suffocating in the back and struggling to breathe.
The vehicle, thought to have travelled from France, was eventually found at Brampton Hut services just before 4.30pm on 17 February.
The three men were safe and not injured and Cambridgeshire police said their welfare was now being handled by the immigration services.
It said incidents like this highlighted that slavery trafficking are real and the police needed the public’s help.
The force said people should call the police immediately if they see anyone emerging from an HGV, especially suddenly or as if in a rush; if they hear banging from the inside of a truck, or if a group of people are heading towards or going inside the back of an HGV.
The police said another warning sign is if produce is being thrown from a vehicle, or something is being done to catch the attention of other motorists.
The warning comes as Crimestoppers appealed to hauliers to help stop people smuggling with the launch of a hard-hitting campaign.
In January, seven men were jailed for a total of 92 years following the deaths of 39 Vietnamese migrants who suffocated in the back of a refrigerated trailer whilst being smuggled into the UK.
