Things with mobiles aren't working, it's why the guidance/law has been changed. Can they ever practically work? Whilst we can have a debate about whether the police are doing 'enough' and various sorts of evidence, it's always going to be incredibly difficult to catch drivers using mobile phones - without a big shift. In this context it's why the penalties were upped. It's just they haven't really worked that well either
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I'm not really sure what the answer is, maybe more like drink driving where if you have an accident it is always (rather than sometimes) investigated whether the phone was being used or not. This would generate work for the police, but in the long term it might be worth it. Even if they got rumbled but couldn't prove it in court, a letter warning them or the knowledge of it being investigated might well change a few peoples' behaviour.

I'm not really sure what the answer is, maybe more like drink driving where if you have an accident it is always (rather than sometimes) investigated whether the phone was being used or not. This would generate work for the police, but in the long term it might be worth it. Even if they got rumbled but couldn't prove it in court, a letter warning them or the knowledge of it being investigated might well change a few peoples' behaviour.