I was told to go to Gosford Hospital which is 40min from where I live - my first contraction didn't start till I got in the car (waters had broken with StrepB so had to go in even though contractions hadn't started). BUT they were less then 5 min apart 1min+ from the get go - the trip was . . uncomfortable to say the least. I was advised to get in the backseat, but I honestly was not going to be comfortable sitting/lying sideways in the backseat as would have felt precarious to me (that and I didn't want to hurtle down the freeway without a seatbelt JIC) so I got in the front seat put the seat as far back as could go and lifted myself semi-standing off the seat with each contraction to relieve that sword twisting up my butt feeling and that was definately the most comfortable. So, I personally would advise the front seat over the back but that could just be me

My SIL was supposed to go to the same hospital with her 3rd, but she felt pressure/pushing as soon as she got in the car so went to the nearest hospital 10min away instead and delivered there so that is an option if you feel you can't cope or it's happenning fast. Plus you can always pull over and call an ambulance in the very unlikely situation that you need to push prior to hospital. Boy, I ramble a lot HTH though. All the best!!!