I was asked, "How do you know when to use a Type 2 vs. a Type 3 Manhole Frame & Cover". The standard drawing shows the weight difference for these but I can not find any other information on these.
Keith L. Smith:Good question. The Type 2 Frame & Lid are rated for H-20 loading and are for pouring into a concrete slab. Std. Plan 604.30 shows 1A, 1B and Type 2 used in the Cast-in-place manholes. Type 2 is used for paved areas, 1A and 1B are used for unpaved areas. In Std. Plan 731.00, Type 2 is also used on unpaved areas where the Alternate Flat Slab Manhole is used (instead of a typical manhole, which is deeper). See also Std. Plan 604.30.
Type Type 3 Frame & Lid are not traffic rated and are for pouring into a concrete slab. Basically, use Type 3 for sidewalks. See Std. Plan 731.10, Sheet 6 of 8.
Type Type 4 Frame & Lid are rated for H-20 loading and can be used as a slab type of casting (poured into concrete slabe), set into corrugated pipe vertically or flip the frame upside down and it will set on top of a structure like the Type 1-C. Although it can be used like a Type 1-C, although we are unsure whether MoDOT uses it that way. Type 4 can be used for sidewalks and precast drop inlets (ex. Type T) where traffic is expected. See Std. Plan 731.00.
After additional discussion (involving MoDOT possibly revising the choices of manhole frames and covers), you may expect some cover selection guidance in the EPG along these lines.