There was a message a few days (week or so back) regarding errata in relation to vehicle passenger carrying capacity. It had slipped my mind and I've now gone back to try and find it and cannot.
Anyway - if this is of any help:
1) Trucks & Lorries (as standard) will carry 2 INF: unit passengers - there will be exceptions noted in the army lists (down to 1 or up to 3) but they will appear in the Notes column in the lists.
2) Half-tracks and Jeeps/4x4s (as standard will carry 1 Inf: unit passengers) - it is highly unlikely that there will be exceptions to this
3) Tanks (as standard) will carry 1 Tank Descant Rider unit (usually INF:)
4). all other units (especially various transport aircraft and amphibious assault vehicles - classified as APCs) have the maximum numbers of units and types of units they can carry indicated in the Notes column of the army lists.
Thanks
Mark