London's bridges are changing, in reaction to recent terrorist attacks.
This was Westminster Bridge in March.
This is Westminster Bridge today, with added Hostile Vehicle Mitigation Barriers.
These were installed last weekend along the full length of the bridge, to protect pedestrians from vehicles driven by anyone with murderous intent.
Vehicles are prevented from entering either end of the pavement area by streamlined metal barriers, of the kind that have been used around Parliament for many years.
Pedestrians are no longer able to cross the bridge, except at either end.
The same thing has happened on Waterloo Bridge.
The new barriers have a temporary feel, but there's no telling how long they might remain, nor whether a more permanent arrangement will be introduced.
Pedestrians used to be able to cross the bridge at any point, via the central reservation. This is no longer possible.
The bridge may be safer for pedestrians but the cycle lane is now about half its previous width, making it more dangerous for cyclists.
A more disruptive installation has taken place on Blackfriars Bridge.
Both entrances to the North-South Cycle Superhighway, and the pavement either side, have been blockaded with heavy metal barriers.
Cyclists are only able to ride through the obstruction in single file, which is causing hold-ups at peak periods.
Here's one cyclist pedalling through the wrong gap to overtake a slower cyclist.
Meanwhile two bus stops on the bridge have had to be closed, because the barriers mean it's no longer possible for passengers to get on board.
The only advice for would-be passengers is a generic notice saying "Please use next available stop", with no indication where that is, or how far.
Oddly at Southwark Bridge, the next road crossing over the Thames, no changes have been made.
The only barrier is a low concrete ridge about a foot high, installed a few years ago as part of the segregation of Cycle Superhighway 7.
Concrete blocks have not been added at either end of the bridge, so it remains perfectly possibly to drive a vehicle up onto the pavement/superhighway for its entire length.
Presumably Southwark Bridge isn't deemed famous enough for terrorists to consider it a target.
London Bridge, however has been swiftly barriered off.
The full width of the bridge used to be potentially accessible to pedestrians, cycles and rogue vehicles. Now cars are kept to the road and pedestrians are restricted to the pavement.
However, the barriers have been erected in a bus lane, which is now too narrow to be easily used by buses.
At the southern end of the bridge is a poignant reminder of why these barriers have been deemed necessary.
If two famous bridges can be targeted by terrorists, who'd bet against a third?
Even Tower Bridge has been given additional protection.
There have been safety barriers across the central span, where the bridge rises, for many years.
What's new are these barriers on the northern approach, where the bridge runs along the edge of the Tower of London's moat.
They're not exactly scenic, compared to the ironwork, but they do prevent vehicles from mounting the pavement.
They also prevent buses from opening their doors.
Two bus stops have been closed until further notice, and again the advice provided is less than helpful.
Inconsistently, there are no barriers on the southern approach.
There are also no barriers at thousands of other spots across London where a vehicle could drive into pedestrians and cause carnage.
This extra protection has served to move the problem elsewhere, and made our bridges harder to use and less safe to cycle across. Let's hope these hasty obstructive barriers won't become a permanent fixture.