I'm glad you're alright. Believe it or not, wheel design and the type of spokes used on your front wheel can have a bearing in this type of accident. It looks like you didn't have an aerodynamic wheel with fewer spokes (they will be more dangerous since they're less likely to deflect objects flipped up from the road). However, even a wheel with more spokes may present a greater risk if aerodynamic spokes that are blade or oval shaped are used since they have sharp edges that may dig in and lodge a stick into place. Here's a link to a discussion from a law firm that handles suits involving bicycle accidents. http://stc-law.com/wheel_roll.html