This is such a tough one, I sympathise. We also live in a cul de sac and to be honest its not the best area (although the house is nice) and some of the other kids that play out aren't who I would choose for my daughter to play with but it is what it is.
She's 6, nearly 7 now and last year was 5 and was constantly asking if she could play out the front because there were always other kids out (including some she recognised from her school who were younger) Explaining that they aren't allowed because they are too young when there is a 4 year old playing out alone is quite tricky!!! Anyway, I stuck to my guns because although she's sensible and mature for her age I didn't think she had the road sense and thought she was too young. This year though she's been allowed out (so she was 6). I was still not overly happy but thought it was unfair to hold her back when all the other kids are doing it. We set boundaries and rules i.e she can only go up to certain points on the street so isn't too close to the main road, she's not to go in this area or that area blah blah) She absolutely loves it!! She plays out from the minute she gets home until bed time (apart from dinner) most nights and during the holidays and weekends all day if she can. I have relaxed a bit more now she's been doing it for a while. I know she's conscious of cars and road safety now and she always checks with me if she wants to play in somebody's house and I keep an eye on her anyway while she is out.
Personally I think 4.5 is a little young however if she is playing with an older sibling who you trust maybe that changes things. Only you can know for your child.
To compromise with my daughter before she was allowed out by herself I would sometimes let her play out front for an hour with my supervision so she could mix with the other kids, ride her bike etc but I would do jobs like clean the windows or the car so I was out at the same time. Maybe that's an option?
