It depends on the geography, the road conditions and the condition of the cyclist. An out of shape cyclist on a steep hill is sure to slow down everyone. A couple of fit ones under the right circumstances may have the ability to outpace the traffic without resorting to running red lights and so on.
The screen shots below were taken over 2 minutes and 50 seconds on Lilyfield Rd. Distance is 1.6km, or 1 mile for us old sods. Take note of the black car.
There were several times when me and the other cyclist were preparing to overtake, but we throttled back because it looked like one of the cars was about to turn left in front of us, or the road narrowed too much to let us go past safely. In other words, cars were holding us up on this particular day.
Lilyfield Rd heading into the city is a fast run. From the corner of Balmain Rd, you get a good downhill and a road bike will rapidly hit 50km/h - which is the speed limit. I've seen crazy bastards fly down much faster than that. It goes into a short uphill before long, but if you have momentum and lots of power in your legs (I have stacks of both), you can maintain a speed of at least 35km/h up the hill and over the crest. From there, it is downhill most of the way to Victoria Rd, and if you still have your lungs after blasting over the first hill, you can hammer it all the way to Victoria Rd as fast as the corners will allow.
If you look closely in the last few frames, you can see that the stream of traffic was held up by a bus up the front.
Funny. We cyclists always seem to be accused by bus drivers of holding every one up.
This is a bit of an exception though. Going the other way, due to the hills, I am usually as slow as a wet week.