I discussed this a bit with my ob and the midwives at the hospital because my first birth was quick (2 hours) and I had lots of time constraints with getting to hospital second time (getting DD1 some where or waiting for some one to come look after her, potentially DH getting home from work, not being able to take DD1 in an ambulance with me if I was home alone etc). One of the very experienced midwives at the hospital said that second labours are often about half the time of the first one, which scared me a bit, not the labour but the getting everything in place in time! I thought this idea was a bit too, well simplistic, so I did a survey of friends and family and online friends and amazingly is was accurate for the majority of women who had spontaneous labours (of course it was all different for inductions and the like). I'm not sure if this necessarily applies for 3rd or subsequent babies, and I'm still not sure if it is all a bit too simplistic, but it is food for thought.

Anyway, my midwives and ob all made sure I had backup plans and things in place just to be on the safe side. I mean hopefully you don't need to utilise them, but personally I would suggest putting a few things in place just in case, like arrangements for child minding if you need it FAST (or being able to take the older ones to hospital with you, which was part of my plan B), ensuring you have ambulance cover or other options for hospitals if that is what suits.

Something to consider also is that babies can get a bit shocked and distressed when it happens very quickly, my DD1 was a bit stunned when she was born and needed oxygen and some help to look lively which was easily taken care of in hospital. If you do get to hospital or plan to be home with a birth attendant or an ambulance gets to you they can look after this if the need arises, but if you literally are on the side of the freeway there is no equipment or expertise to do it. So not a huge risk because lots of babies are born quickly and don't need help, but just a point to consider and perhaps try to have some vague plan in place to avoid the freeway side delivery (and the embarrassment of being 'that' woman on the news who had her baby on the side of the road LOL!)