As of Wednesay, 1 August 2007, catostrophic bridge disasters were rare. After the events of Wednesday [1], catostrophic bridge collapses remain rare, and will remiain rare.
We have evidence in video [2] form. and from the Northwestern University, Infrastructure Technology Institute [3]. Bridge disasters have happened about every decade or so. There no reason to believe the frequency will not decrease. We learn from our experience and get smarter. Further, there is no evidence of anything which would suggest an increase in frequency. Rare events do not become common events without a reason.