Value capture: A benefit receipt tax?

Among the ideas proposed by Citizens League on transportation policy (in 2005 and 2008) is a "benefit receipt tax," which will be collected at the point of sale of land that benefits from a transportation improvement.

Bob DeBoer in Citizens League shares an example of a land sale based on a highway improvement where the assessed value was in the $500,000 range and the land sold for over $3 million. In such a case a benefit receipt tax "based on a percentage of the amount above the assessed value" may be an effective way of "value capture" to partially recover "the level of benefit that should help pay for the transportation improvement." 

This sounds a great idea. But the first concern I have is about the timing of sale. Over time the assessed value would catch up with the market value and make the value gain less discernible. So the benefit receipt tax may just deter or delay the sale of land. It probably makes more sense to have an annual levy based on the the assessed (land) value rather than to have an one-shot collection at the point of sale.