Your argument is the fallacy of false dichotomy. We know nothing unless we have data. Let's break this down.
First, what is your criteria for valid data? Traffic? Accidents? If we have valid data, what numbers represent success/failure? Is a 10% increase in traffic along side streets a failure? 
By "data" I assume you mean numbers. What of evidence from users? We know the neighborhood association has deemed it a favorable outcome. Is this an indicator of success? If we found side streets through this neighborhood had increased traffic and yet the association said they are in favor of the project, is that not success?
Shall we dismiss other sources of data? Some business owners have come to favor the project. Probably some don't. Very few allowed the city to look at financials. What do we make of these facts?
I think we can make some assumptions about the success without your claim that we need certain data to know anything. I will state the successes are greater than before.