In DC there are a bunch of lettered streets.

I and J and U caused problems...

Is this a national database, or it it restricted to local roads? If it's national / regional, you might want to look at how the USPS standardizes addresses. This must be a solved problem, and you might save yourself some work in seeing how they do it - I think they even have an API that other sites can use.

Or maybe not - I'm no expert. But it's an interesting problem!

Good luck.