SPEED, does it effect safety in a city

[Kookas]

The faster you go, the lower the number of cars coming from behind that you encounter, so if cars behind you are your main danger then yes it's safer. Not to mention if you're going fast enough, the cars that do catch up behind you won't overtake as often.

That said, the faster you go, the more of a danger people pulling out on you/people stepping or running out into the road pose.

 

[mustang1]

In a traffic jam whole filtering, I slow right down.

While in traffic but able to use the oncoming lane (when its free of course), I'll speed up somewhat but need to be mindful of drivers coming out of side roads and not expecting to me to be there.

On long stretches of straight road, I'll pile on some megawatts.

 

[crazyjoe101]

I much prefer cycling closer to traffic speed in London, to a point. If I get up towards 30mph (obviously there would need to be a slope or tailwind to sustain this for any time, I'm not claiming to be some sort of pro here) I get a bit jittery as my chances of avoiding a sudden obstacle are low, hence why I'll normally match the traffic speed unless it's over 20 or really low, in which case I'll be filtering on the driver side. At 20 or so I can just sit in primary where I am away from car doors and am highly visible to other road users without holding anyone up which makes me feel less pressured. At a lower speed I find it harder to get away from the curb and into primary to get around parked cars because I'll sometimes get trapped by a constant stream of traffic to my right whereas at a higher speed, the gap between cars is longer and I feel I have an easier time merging into primary.
I think when it comes down to preference; I would rather risk hitting a car pulling out of a sideroad than have a vehicle alongside / overtaking me when I do not want it there as at least I can see the impact coming. As far as the pedestrian part goes, I find my speed in the pedestrian heavy parts of London is low enough to stop or swerve whilst still matching traffic speed as most of it just trundles along to the next red light if it's moving at all.

 

[Full Metal Sprocket]

Cant say,around the Cannon Street backstreets I have to cycle slower as at various times there are many pedestrians around.Depends on circumstances I guess.