Read the passage and answer the question. 'When the state government banned commercial motorcycles from the major roads of the capital, it argued that the measure would reduce accidents and curb crime. Six months on, the accident figures have indeed fallen. What the official statements do not mention is the army of young men who woke up one morning to find their only source of income declared illegal. Some have turned to tricycles; others have drifted back to the villages; a few, the police admit privately, have joined the very criminals the ban was meant to check.' The word 'curb' as used in the passage means