Through the 1970s , the proportion of urban bus routes operated with conductors declined , as older vehicles were steadily replaced with new buses equipped for one - person operation .
Operators grappled with staff shortages , rapidly increasing costs and falling usage .
Through the 1970s , the proportion of urban bus routes operated with conductors declined , as older vehicles were steadily replaced with new buses equipped for one - person operation , and operators grappled with staff shortages , rapidly increasing costs and falling usage .