A Thomson Road Steamer at Edinburgh This steamer , with wheels bound round to a depth of five inches with an indiarubber tyre , was invented in 1868 for hauling loaded waggons above sharp inclines , " to the intense disgust of coachmen , and to the terror of nervous invalids in carriages . " In 1870 it was adapted as tractor for an omnibus , " a handsome and commodius vehicle , with only two wheels , built to carry 65 passengers - 20 inside and 44 out . 1870