Ama-semi trailer ethangi lensimbi engagqwali aklanyelwe ukuthutha uketshezi oludinga amazinga aphezulu okuhlanzeka nokuhlanzeka, njengemikhiqizo yokudla, imithi, namakhemikhali. Izakhiwo zensimbi engagqwali ezingagqwali zikwenza kube ukukhetha okuphelele ekuthuthweni kwezimpahla ezibucayi ezidinga ukuphepha okuqinile kanye nezindinganiso zokukhucululwa kwendle. Lawa ma-trailer avame ukusetshenziswa ezimbonini zokudla, iziphuzo, nezemithi, lapho ukuhlanzeka nokuphepha kubaluleke kakhulu. Ama-trailer amathangi ensimbi engagqwali ahlinzeka ngezinga elingenakuqhathaniswa lokuvikela ekugqwaleni nokugqwala, okuqinisekisa ubuqotho bokuqukethwe kugcinwa kukho konke ukuhamba. Indawo ebushelelezi yensimbi engagqwali futhi yenza lawa ma-trailer ahlanzeke kalula, avimbele ukungcoliswa kanye nokuqinisekisa ukuthobela imithetho yokuphepha kokudla. 

Lawa ma-trailer atholakala ngosayizi abahlukahlukene futhi angenziwa ngendlela oyifisayo ngezindonga ezivalekile namasistimu okulawula izinga lokushisa, okuwenza abe nezinto ezihlukahlukene ekuthutheni kokubili uketshezi olushisayo nolubandayo. Ukwakhiwa okuqinile, okuqinile kwama-trailer amathangi ensimbi engagqwali kuvumela ukuthuthwa okuphephile kwamakhemikhali, uwoyela, nolunye uketshezi oluyingozi, okuwenza abe yinketho ethenjwayo ezimbonini emhlabeni jikelele.