Changing the Guard switches to fixed days amid tightened security
The Changing the Guard ceremony at Buckingham Palace is switching days as part of tightened security measures.
From 16 January, the spectacle will be held on the same days each week - Mondays, Wednesdays, Fridays and Sundays - rather than alternate days.
The Royal Parks said the three-month trial was aimed at making it easier for tourists, motorists and businesses to plan ahead.
Roads have closed during ceremonies since December's Berlin market attack.
The Royal Parks spokesman said the ceremony would also take place earlier in the day - between 10:15 and 11:45 GMT - so the roads could reopen in time for lunchtime traffic.
This means the actual changeover will happen at 11:00, rather than 11:30 from mid-January until March.
"This new programme allows the public, visitors, motorists and businesses to forward plan following new road closures on guard change days which were introduced in December as part of ongoing security measures aimed at keeping the public safe," the Royal Parks spokesman said.
From April to July, Changing the Guard takes place every day.
An Army spokesman said it had not been decided whether to switch the daily event to set days in the summer as well.
Twelve people were killed and dozens injured when a lorry ploughed through a Christmas market in Berlin on 19 December.
Days after, the Royal Parks - which manages roads around the palace - shut vehicle access during ceremonies to Constitution Hill, the Queen Victoria Memorial, Spur Road, Link Road and The Mall up to the junction with Marlborough Road.
The Metropolitan Police said the closures were a necessary precaution due to the event's high profile, large crowds and substantial military presence.
Extra security barriers around the palace were also put in place.
The popular spectacle, which attracts thousands of tourists every year, sees the Old Guard - the soldiers currently on duty - formally hand over responsibilities to the New Guard, usually accompanied by a band or a corps of drums.
The guardsmen, typically from the Household Division, are identifiable by their distinctive red tunics and bearskin hats.
The scale of the ceremony is governed by the Queen's presence. If the Royal Standard is flying above the Palace, the Queen is in residence and the number of sentries is increased.