Hundreds of times a year, but I think perhaps once a day.
Now, many of those incidents are occurring at very low speeds in rail yards and so on, but it's not only driver inattention; the interpretation of those signals is extremely complex. There are many, many different colours of light indications. The colour and position of the lights are all you have to go on. There is no readout in the locomotive cab that tells you what the signal means, unlike railways in most other parts of the world, and there's no backup should the crew, for whatever reason.... And we will never know the reason for the Burlington crash, because we don't know exactly what was happening in that cab, hence the recommendation for cameras and audio recording.
On the third recommendation on protection of the actual driver's cab, that was a tragic way that accident unfolded, with the way the locomotive collided with a concrete building beside the track. That particular thing, while important, we don't view as being nearly as important as addressing the need for positive train control.