Back lighting

Not a cry for help, just some experience.
The position of the barriers was putting the drivers directly up-sun of us, fine for the autograph hunters but hard for photos.
1) don't trust the lens hood
... this is flare on the front element, and there's no contrast
2) shading the front of the lens with your hand works
... but only with a SLR can you see what you're doing !

Even fill flash couldn't rescue #1

3) increasing flash does not IMO improve the result

I think the second one is the better of the lot, but I also think you could do something with all of them in Photoshop. Did you shoot these in RAW mode at all.

Interesting getting shots of Mark Webber.

Also did you know you Leprechaun image in your signature isn't showing Paul.

Also remember when saving them for the web you should have them in sRGB mode for web browser otherwise they might not look the same as you intended them to.

I know the purpose of your question was to seek help in metering with back lighting, my only intention here was to show they could be saved as well.

I think the second shot is about the best you could have gotten in a situation like this. The flare isn't bad either, you could easily clone that out in Photoshop. Lens hoods actually make a big difference; they would likely have had more problems without one. Dedicated hoods - the ones made by the lens manufacturer specifically for that lens - will give you the most benefit.

Fill flash is going to help a lot but it won't do everything. You could also try spot metering off the driver's face and with caucasian skin tones open up one stop from what that reading is. IOW, if it says 500 at f8, shoot 500 at f5.6. It will blow the background highlights, but the subject will be properly exposed. There are limits to the medium (film or digital), it can record only so much. Color neg won't do this as much as digital, but it's got it's own peculiarities. With some situations, it's just next to impossible to get the results you want.

Though personally I really like the way the second image looks, I would have avoided the flash altogether and let him get that ethereal glow that backlit subjects can get when you expose for their shadow side. However, since it doesn't seem you were going for that, why not just expose for the background and let the fill-flash do its thing and fill in the subject to match? Just tilt the camera above his head, set it appropriately, and then reframe and let TTL work its magic.