I have found another archive of California Highways and Public Works PDF scans online at: http://libraryarchives.metro.net/DPGTL/Californiahighways/. I am not sure if this has been posted on the forum or not, so I thought I'd share just in case you haven't yet seen it and are interested.
I found it a while ago but haven't tried to mine it. Here is how the two versions compare:Internet Archive version
--essentially complete (except for missing issues early on, and the occasional missing page later on) between 1924 and 1967. (CH&PW
was published from 1923 to 1967.) This version was scanned from bound originals kept at the Seattle Public Library. Each page consists of multiple raster images arranged on top of each other in layers for more efficient compression, which yields satisfactorily readable text but very poor rendition of continuous-tone images, with large gaps between nearby tones that show up as blocking. PDF is the container format I used, but I think the volumes can be downloaded in DjVu format as well--I don't know if rendering of continuous-tone images is improved in DjVu, which in theory is a multi-resolution format but in practice can be deployed in much the same way as PDF raster layers. Accessibility, in my experience, is improved by converting the PDF pages to JPEG in Acrobat
(which expands the aggregate filesize by an approximate factor of six: 1.51 GB in PDF, 10.3 GB in JPEG) and writing scripts to steer an image browser to a volume-number-page reference entered at a command prompt. This conversion process yields page images with an uniform resolution of 2330 x 3363.LA MTA version
--Runs from 1924 to 1961 and is (presumably) scanned from originals kept at the LA MTA office library. Each page consists of a single raster scan (24-bit, I think, since blue document stamps show up as blue) at an uniform resolution. The resolution chosen is fairly low and compression level is fairly extreme, so JPEG artifacts are bad. Continuous-tone images render well but text looks watery and indistinct. PDF is the only container available and organization is by issue rather than annual or biennial volume (in other words, each PDF file contains one issue). Image resolution is variable--either 1040 x 1460 or 2060 x 2940--and it is unclear what rule is used for choosing the resolution in any given instance (there are, for example, many pages of fine print at the lower resolution).