At the most basic, if your table is "tData" for lack of better name and your particular variable used not provided,
tG=groupcounts(tData,{'TTC','ConflictType','Veh1type','Veh12ype'});
will return a table of counts for all groups; you can then select from it the record(s) with TTC==1; the above would produce only one, of course.
The question with more data is whether/how to count the subcategories if are more than one or to add them altogether for the count. We don't have that complete a definition of the desired output.
There are a number of grouping functions available, see the list of functions in the doc at the top of the doc page for the above for further ideas.
Or, if it is really only the one single set of specific values that is of interest, then logical addressing --
tData=convertvars(tData,'ConflictType','categorical'); % set appropriate variable type
ix=(tData.TTC==1)&(tData.ConflictType=="rear end")&(tData.Veh1Type==630)&(tData.Veh2Type==630);
nCounts=nnz(ix); % just the counts, ma'am...
tSubset=tData(ix,:); % select the subset --> number would be height(tSubset)
