Oop Late

Is it wise to let it get so low?
Has this happened to you?
There you are driving along and you glance down at the petrol gauge. The petrol gauge says it is very close to empty!
Now I really want to get to work before I am late and all the garages seem to have queues a mile long (well almost!) so I decide to carry on and get my petrol later on in the day.
Needless to say I did not remember. With every mile I take I am pushing my luck and promising myself that I will definately fill up at the next petrol station. At a guess I reckon I have travelled approximately another 15 miles or so until I have topped the tank up.
I have a Toyota RAV4 and in my user guide it says “when the petrol light comes on you should fill up soon.” Well “soon” means different things to different people. Can anyone tell me how many more miles they have managed to travel when the fuel light shows red? My husband drives a peugeot and his manual says “when the petrol light comes on you can go approximately 30 more miles.”
I suppose I could experiment by topping up the petrol can that I keep for emergencies (usually empty I may add) and fill it up and drive in a quiet residential area until the petrol light comes on. Set the milometer and drive til the tank is empty. Then I would know how far I can go before I run out completely. Simple idea, but probably not good for the engine.
I suppose the sensible thing to do would be to go the other way and never allow the tank to fall below three quarters empty because surely at the end of the day it really is so much hassle having to panic at the last minute and find somewhere to fill up!
I would be interested to hear how many miles you have managed to get after the red light has appeared!
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