Assume you have a boundary file for, say, census tracts with population and a street layer.
Select the polyline feature representing MacArthur Blvd.
Create a 500 m buffer around the selection.
Use geoprocessing>intersect on the buffer and the census tract polygons.
Assume that the population of each census tract is uniformly distributed so we can use the area of the intersection with the buffer to estimate the population that lives within 500 m of MacArthur Blvd.