Seems like they could cut out a lot of that code by using macros. Here's a quick and dirty Common Lisp script that reads the CSVs from the .zip file and generates classes at runtime using the headers in each CSV for the slot names. It also defines a 'select' function to make queries easy to write. It's a little too long to post here:

https://gist.github.com/jl2/fd324fa3faa919803152465fade14b6b

And here's what it looks like to use it:

    CL-USER> (defparameter *transit-data* (read-transit-data "~/Downloads/gtfs_current.zip"))
    
    CL-USER> (select (table *transit-data* :stops) 'stop-name "PIERNE")
    
    ((STOPS  "PIERNE01"  ""  "PIERNE"  ""  "49.102273"  "6.179863"  ""  "http://lemet.fr/screen/index2.php?stop=257"  "0"  ""  "1")
     (STOPS  "PIERNE02"  ""  "PIERNE"  ""  "49.102558"  "6.179825"  ""  "http://lemet.fr/screen/index2.php?stop=234"  "0"  ""  "1"))
    
    CL-USER> (select
      (select (table *transit-data* :trips) 'trip-headsign "L5a - MAISON NEUVE")
     'route-id "5-77")
    
    ((TRIPS  "5-77"  "SMIN_H1920-CLaS50V2-Lun-Sam-98"  "409137-SMIN_H1920-CLaS50V2-Lun-Sam-98"  "L5a - MAISON NEUVE"  "1"  "60112"  "50057")
     (TRIPS  "5-77"  "SMIN_H1920-CLaS50V2-Lun-Sam-98"  "409138-SMIN_H1920-CLaS50V2-Lun-Sam-98"  "L5a - MAISON NEUVE"  "1"  "60111"  "50057")
     ;; ...
    )