Ancestry.com has a very useful street index to the 1940 census, in advance of the name index. Crabtree Street is listed in Durham Ward 5, section 32-43. There are 48 pages in this set. In a quick page-through, I found a few houses on Crabtree on page 28, and more on pp. 32-33. A lot of the street names are hard to read, but judging from the ones I can make out, this seems to be the area north of Duke Hospital, including Pettigrew Street, Crest Street, 15th Street, and Fulton Street. The Durham Freeway (NC 147) now runs through this area, and its construction severely impacted the neighborhood. My guess is that the Crabtree Street in this section of the census no longer exists, and that it's not the same as the Crabtree Avenue that you found near Carver Street.