Isikhongozeli yiyunithi yokupakisha imithwalo esemgangathweni esetyenziselwa ukuthutha iimpahla. Ngokuqhelekileyo yenziwe ngetsimbi, intsimbi okanye i-aluminium kwaye inobukhulu obuqhelekileyo kunye nesakhiwo sokuququzelela ukuhanjiswa phakathi kweendlela ezahlukeneyo zokuthutha, ezifana neenqanawa zempahla, izitimela kunye neelori. Ubungakanani obuqhelekileyo besitya buziimitha ezingama-20 kunye neemitha ezingama-40 ubude kunye neemitha ezi-8 kunye ne-6 ukuphakama.