With 1.5hr drive, I would definitely not be leaving as late as possible - I would be leaving as soon as I knew it was established labour. Even if when you got there you didn't go straight to the actual maternity ward.
(then again, I am stressing that I won't make it to the hospital on time because I have a 45min drive and my DH works 30mins away from my house: my last labour was only 2hrs start to finish.)

I have been in full blown labour and in the car with every pregnancy (I go straight from nothing to full blown). It is horrible. You cann't get comfortable. Every bump, and curve in the road is agony. I cann't really give you any tips to get through it, because nothing actually helps - you just have to grit your teeth and bare it.