To use this website:
Step 1. Choose your street name, then click the search button.
Step 2. To limit it, choose under limits field box, then click the search button again. This will allow you to get to the specific area.
Step 3. Once the street is found, under Key Map Results, you will see a 3-column box that has "dedicated", "grade" and "monument". Click on the "grade" (it's clickable). This will get you to open the image of the street. Many of the streets have grades written down.
If you get a ticket for not setting your wheels properly and you believe that you shouldn't have to, you could use this DPW website to use a defense that the street is 3 degrees or less!