A geographic information system (GIS) network data base is used to determine the characteristics of 397 routes used by commuter cyclists in Guelph, Ontario, Canada, and to compare them with the shortest-path routes between each origin and destination. The analysis of route data provides useful insight for understanding factors affecting travel behavior and in this case provides quantitative support for many existing assumptions regarding commuter cyclist behavior. Most commuters divert very little from their minimum path (0.4 km on average) and are found to use major road routes. The cyclists tend to avoid grades, grade-separated railway crossings, and high-activity areas, but not road (as opposed to pedestrian) bridges. Cyclists use traffic signals especially for crossing major roadways and turning. The high-quality direct off-road paths are used only infrequently by the commuter cyclists and the lower quality ones even less. The results of this analysis suggest that efforts to accommodate current commuter cyclists should be focused on improving cycling conditions on the road network, such as providing wider curb lanes, or actuated traffic signal detectors that recognize the presence of bicycles. If potential new commuters are similar to the minority of current commuter cyclists in this study who use mainly local roads, paths or trails, then projects that make the network of local roads and pathways more connective and direct may encourage a higher level of commuter cycling.