The area where this is occurring is along that last segment of 99 to be converted to full freeway between the Madera county line and the southern outskirts of Merced. While it was being constructed, traffic -- in both directions -- was diverted onto what was a constantly changing set of alignments consisting of portions of the original highway (situated near the adjacent RR line), completed carriageways of the new freeway wherever feasible, or one or another of the frontage roads (one of which functionally replaced the old alignment on the west side of the freeway). Unusual for D10, the design featured quite a bit of frontage roads -- but those would flank the freeway for a while and eventually curve off as part of the local grid (D6 to the south really liked frontage roads in rural areas, but those tended to hug the flanks of the freeway quite closely and only occasionally segued into local grid patterns -- but then, that section of 99 was oriented much more N-S than the section near Merced, which is almost a 45-degree diagonal. With all the changes and temporary alignments serving as through lanes of CA 99 during the long construction process, it's likely that some frontage-road bridges were mileposted along the way -- and that at some point the Google car came through, which would tend to archive one or another of the interim configurations -- and subsequently show up on GE/GSV when specific road names are keyed in. When I saw the "Reply #63" post, I immediately googled up Silveira -- and it pointed to the east frontage road. Although the nearest community referenced was Athlone, Le Grand, about 5 miles to the east along the mostly parallel BNSF tracks, is probably the USPS reference town for the immediate area.