1\In HongKong,cars,buses and bikes usually keep to the left side of the road.这句话的keep to 起什么作用?

1\In HongKong,cars,buses and bikes usually keep to the left side of the road.这句话的keep to 起什么作用?
1\In HongKong,cars,buses and bikes usually keep to the left side of the road.这句话的keep to 起什么作用?

1\In HongKong,cars,buses and bikes usually keep to the left side of the road.这句话的keep to 起什么作用?
keep to the left side 靠左行驶,keep to我觉得就是谓语而已,没有什么特别的意思