Join Wiltshire's Roads Policing Unit as they use an unmarked heavy goods vehicle to catch drivers breaking the law on the M4. Operation Tramline uses a cab owned by National Highways' that allows the police to see inside all types vehicles, giving officers a view that simply isn't possible from a regular traffic car. As you can see from this video, drivers using their mobile phone is a common offence. This is one of our fatal five offences - all of which increase your chance of being involved in a fatal collision. Operation Tramline is a National Highways' initiative supported by Wiltshire Police.