Some digging around through the online records of the Multnomah County Surveyor showed that Interstate Avenue hasn't always been Interstate Avenue. Interstate Avenue jogs to the west at about N. Mason Street. North of that jog, Interstate Avenue was named Patton Street in 1887 (see the plat of Riverside Addition) and Patton Avenue in 1909 (see the plat of Havelock). By 1919 it had been renamed Interstate Avenue (see the plat of Principle Addition).
South of the Mason Street jog, it had been named Maryland Avenue, and what is now Massachusetts Avenue, a block to the west, was originally named Patton, after Matthew and Catherine Patton, who owned land along that street in the 19th century. (It's the street that's now in line with the northern part of Interstate Avenue.) The Pattons modestly called the street "A Street" when they platted some of their land in 1887.
What happened between 1909 and 1919 to cause the City Council to rename Maryland and Patton Avenues to be Interstate Avenue? The answer is that in 1916, the eastern of the Interstate Bridges opened to connect Portland and Vancouver, and the highway people condemned bits and pieces of additional land (including the Mason Street jog in Interstate) to make Interstate Avenue the main road between central Portland and Vancouver. (This bridge was the first bridge between Oregon and Washington.) So there is a certain historic significance to the existing name, and that presents a problem for the City Council, which is being asked to decide next week whether to rename Interstate Avenue for the late Cesar Chavez.
What's the problem? The problem is that Chapter 17.93 of the City Code sets out stringent criteria that must be met before the City can rename a street to honor a deceased person. One of the criteria is that the City cannot rename the street if the existing name is of historical significance. In this case the existing name is of historical significance, representing not the whim of a defunct developer but (I surmise) the decision of a long-ago mayor (likely Mayor George L. Baker, whose term started in 1917) and his Council to commemorate the opening of the first bridge between Oregon and Washington by renaming the street leading to the bridge in celebration.