Just a heads up to warn you of a couple of things in the run-up to Tet in Hanoi. Firstly, although the streets will be very quiet over Tet, at the moment they are extremely busy. This is primarily because people are out and about more buying things in preparation for Tet, and also because there are more deliveries going on, for example of Tet trees and blossoms. So take even more care when crossing roads and allow extra time for any travel around town.
This extra traffic has also led to some taxis refusing to take fares to places they know will be busy, or wanting to charge a high fixed rate. As far as I can tell, the big taxi companies are still sticking to their meters but as they're in short supply right now - because of the time of year - you might end up having to pay a bit more to appease the driver for sitting in traffic. For some journeys, for example around Old Quarter, it might be quicker to walk. Xe om and cyclo drivers might also be pushing up fares both because of the traffic and because they want some extra cash for Tet. It's you decision whether to accept the price or not.
Finally, note that everything else is likely to go up in price too. I parked my bike at the station the other day: it clearly says 2,000VND on the sign and on the ticket but the parking guys were charging 5,000VND. And that was to everyone, not just me. There's little point arguing in situations like this, just pay up - unfortunately it's a symptom of the time of year.