Knowing reliable measures of urban cycling speeds is helpful for:
-planning various types of facilities (e.g., turning radii),
-traffic flow estimations,
-better understanding the degree to which various users can comply with harmonious co-mingling,
-modelling exercises (e.g., accessibility metrics),
It is often thrown out there that speeds for cyclists who travel in urban areas hovers about 10 mph. What do we know of this? Any value, we would expect, would have wide variation. A compilation of a bunch of studies prior to 2000 suggested that free-flow bicycle speeds appears to be somewhere between 6.2 mph and 17.4; the majority of the observations were between 7.5 and 12.4. Of course a lot of the variation is explained by which type of facility the data are from.
Some other or follow up work found values of 9.2 mph during a recreational event that included adults and children, 13 mph along greenways in Indianapolis and 15.4 mph along a separated path in Denver.
Does this vary by city, time of day, or time of week? Hard to say. Studies using similar methods found average speeds in Toronto to be 9.3 versus 11. 6 in Ottawa. The most interesting revelation is coming from some 11.6 million bicycle trips analyzed as part of the Lyon bikesharing system. The average 2.49 km trip took 14.7 minutes—converting to 6.2 mph—much slower than the above values, probably owing to heavier bikes and more congested conditions. They observed some uptick in speeds during rush hour (people are more pressed for time). But here is the interesting nugget: wednesday morning speeds were systematically higher than other weekdays—a phenomenon the researchers suggest might be because of the higher proportion of (faster) masculine bikers, since a significant fraction of women stay home to care for children on Wednesdays.
It looks like 10 mph is a safe and reliable average.
 Along greenways in Indianapolis: Lindsey, Greg and Nguyen Luu Bao Doan. 10 Questions about use of urban greenway trails. in Paper presented at Southern Illinois Transportation
Alternatives Conference, 2002.
 Bike path in Denver: 8. Khan, Sarosh I. and Winai Raksuntorn. Characteristics of passing and meeting maneuvers on exclusive bicycle paths. Transportation Research Record. 1776,
2001: p. 220-228.