A speed limit of 40km/h will be imposed on a much larger part of Sydney's central business district in an attempt to reduce accidents involving pedestrians at night and in the early morning.

A reduction in the limit from 50km/h will come into force in April and cover an area bordered by Macquarie and College streets in the east of the CBD and Central Station in the south. It increases the size of the existing 40km/h speed zone – which also applies to cyclists – by about three-quarters.

The danger time for pedestrians is often at night and the early morning. Credit:Anthony Johnson

The changes are aimed mostly at improving pedestrian safety between 6pm and 6am because, as the state government concedes, congestion often prevents motorists from driving faster than 40km/h during the day.

Roads Minister Duncan Gay said the "greatest enemy" to pedestrians was often confusion among motorists about speed limits.