CTM1 map files created from US Census Dept. TIGER data use the attribute 'CFCC', which gives the feature type. CFCC stands for Census Feature Class Code.
The original CFCC codes are made from an uppercase letter followed by a two-digit number. The codes used in CartoType's CTM1 data format are entirely numeric. The uppercase letter is replaced by one or two digits, using the range 1...26 for the letters A...Z. Thus A08 (road with rail line in center) becomes 108, and X00 (feature not yet classified) becomes 2400.
For roads, CFCC codes are translated into CartoType road types, which are explained in the previous section.
There is a list of CFCC codes at http://www.census.gov/geo/www/tiger/tigerua/ua2ktgr.pdf (in Chapter 3).