The Gann Republic road numbering scheme is influenced by a mix of different real-life countries.
Routes numbered 1-10: Primary national roads. These roads operate from border to border within the Gann Republic. Odd-numbered routes generally operate in an east-west direction, though the alignment of the coastline runs in a southwest-to-northeast direction. Even-numbered routes generally operate in a north-south direction, but can and often fail to follow an north-south axis. All primary national routes connect to an urban area (large or small). The only exception is #10, which is assigned to an non-motorway urban loop or bypass. Such routes can be limited-access trunk routes, full access primary routes, or "Jersey Freeways" (routes with full local access but no breaks in the median; grade-separated junctions and roundabouts serve as "turnarounds")
Routes numbered 11-99: Primary national routes - spurs from roads 1-9. These routes branch off from their "parent" route, i.e. routes 11 through 19 branch off of route 1, 21-29 from route 2, etc. The only exceptions are routes #20, #30, #40, #50, #60, #70, #80, and #90; which are assigned to an non-motorway urban loop or bypass. Such routes can be limited-access trunk routes, full access primary routes, or "Jersey Freeways" (routes with full local access but no breaks in the median; grade-separated junctions and roundabouts serve as "turnarounds")
Routes numbered 100-199: Motorway routes - fully limited access high-speed roadways. These roadways generally follow parallel and/or bypass their Primary national route counterparts and often connect to said routes (i.e. 101 will follow 1, 102 will follow 2, 155 would follow along 55, etc). The exceptions to this rule are routes 100, 110, 120, 130, 140, 150, 160, 170, 180, and 190; which are assigned to orbital and bypass routes and are found along their respective "parent" motorway (i.e. route 110 would be along route 101, 120 along 102, etc.). These orbital/bypass routes can be repeated for every urban area, with a letter suffix which increases along the parent motorway route in order from west-to-east or south-to-north. Examples of this would be 110A for the first bypass/orbital, 110B for the second, etc. In cases of large urban areas with complex motorway systems, the motorways will have numeric suffixes (i.e. 1100, 1101), with odd numbered last-digit are spurs, and even-numbered last-digit routes either serve as another orbital, or connect to another motorway not already found along a primary route. These numbers do not repeat, but increment first within the same urban area, then picking up on the next increment in the next urban area.
Routes numbered 200-299, 300-399, 400-499, 500-599, 600-699: These are secondary routes found in various state roadways, akin to state routes in the US or "B Routes" in the UK. These are often (but not always) former Primary routes which have been bypassed, and will often share the last one to two digits with the old primary route (201, 301, 401, ect. was a former routing of 1, for example)
Routes numbered 700-799, 800-899, 900-999, 1100-1999, or any other number beyond 1999: These are tertiary routes found widespread throughout each administrative area and country-wide. These would be akin to County routes (though not bound by county boundaries) in the US or "C Routes" in the UK. There is no logical organization to these routes.
Routes numbered 9000-9999, though rare, signify special tollways which do not correspond to a motorway or other route.
To note: If you were to query the roadways in the Republic, the number of lanes on a two-way single carriageway indicate the total number of lanes in both directions - an even number indicates a n/2 lanes in each direction; an odd numbered value can mean suicide lanes, climber lanes, or turn lanes. The number of lanes on a one-way roadway (part of a dual carriageway or one-way couplet) indicate the number of lanes in that direction.