SAP Transportation Management aims also at multi-modal scenarios making it necessary to know a bit about the different definitions, what they are used for, and their effect on the solution.
Basically, there are 3 types to steer multi-modal behaviour: Transportation Mode Category, Transportation Mode (Code), and Means of Transport.
Transportation Mode Category: This is a fixed domain value with range [Road, Rail, Sea, Air]. It is used by the system to distinguish processes on a high level (for example decide which user interface shall be used), or the determination of icons and indicators. The Transportation Mode Category must be set for each Transportation Mode (Code), but does not appear on any TM UI later on. There always Transportation Mode (Code) is used.
Transportation Mode (Code): Why is there always the Code in brackets? Well, a bit of history. In the SCM basis there has always been the Transportation Mode, which is a CHAR10 field. Unfortunately, this does not match the ERP definitions. So with SAP TM 8.0, the new Transportation Mode Code has been introduced as a CHAR2 field. TM now defines its own view on Transportation Mode (Code) and the CHAR10 is obsolete. So never use the SCMB customizing activity to define Transportation Mode (Code), use the TM specific view instead(under Transportation Network).
A quite confusing field is the ‘MTrCat’. This is actually EH&S (Dangerous Goods) specific and documented via the F1 help. For a basic setup this should not be required.
The Transportation Mode Code is used in TM to create customer specific scenarios and can be set in different document types. It appears on the UI where required.
Means of Transport: The MTR finally is used to distinguish vehicle types below a Transportation Mode Code, which is a mandatory field in the customizing activity. The above told story of Transportation Mode (Code) made it necessary to also have a specific TM MTR definition using the CHAR2 Transportation Mode Code. So again: Never use the SCMB activity for MTR, but use the TM specific activity instead (under Master Data).
Within the MTR definition you can make setting for example for distance determination, cost, planning attributes. Specific MTRs can be used when defining resources, or in the schedule.
When setting up a customer scenario, think early enough about the consequences of Transportation Mode / Means of Transport definitions.