Is anyone able to help with a car mechanical diagnosis?

My Holden 2002 Barina (bought in 2003) has had all its services and due shortly for 65000km. On Friday out of the blue, it just died on me. I was driving in the tram line (yep, this happened on the tram lane) and my little car just died. It was as if I had turned the ignition off. Got it over to emergency lane and tried to start it. It was cranking but not firing up. RACV turned up and they opened the bonnet and guess what? My car magically started up. RACV guy was not impressed. I swore black and blue it happened but he didn't believe me. So I started off to my mechanic only 500 metres away. Made it 450 metres before it happened again. RACV no where in sight. I waited about an hour in scorching heat of 38 degrees. Car started up and made it to the mechanics. He ran it for 40 minutes before it died for him in the shop. He then replaced the crank sensor. $320 later I picked up my car. Got about 5km and it died on the 4 lane highway. So unsafe. Has anyone got any ideas what's up?