Level of service criteria
Presently, the Highway Capacity Manual does not define level of service (LOS) criteria for bicycles. For other modes of transportation, however, the term LOS is used to characterize the operational conditions of a roadway with six designations (LOS A through LOS F). The descriptive terms in the written definition of LOS include speed and travel time, comfort/convenience, traffic interruptions, and freedom to maneuver. While this concept and the subsequent defining terms were originally developed for motor vehicle applications, the qualitative descriptors of comfort/convenience and freedom to maneuver are most applicable to bicyclists traveling on the roadway in the presence of motor vehicles.
The LOS definition also states that it is the userís perception of the operational conditions within the traffic stream that dictates the ranges of qualitative measures included in each LOS designation. The perceived comfort level of bicyclists within a given set of operating conditions on the roadway is exactly what the BCI model produces. Thus for bicycle LOS, the measure of effectiveness (MOE) should be the BCI. Subsequently, each LOS designation should be defined by a range of values produced by the model. To remain consistent with the Highway Capacity Manual, six LOS designations (A through F) should be defined. A discussion of how these ranges were developed follows.
As a starting point, the distribution of overall mean comfort level ratings (averaged across all subjects) by site was examined. The site with the lowest rating produced a mean of 1.24; the site with the highest rating resulted in a mean of 5.49. The conditions included in the video survey and rated by the participants included a broad range of conditions. These sites were selected to range from environments that would be comfortable for every adult bicyclist to those that would not be comfortable for even the most experienced commuter bicyclist. Likewise, the participants in the study ranged from the very timid casual bicyclist who might ride once a month and only on off-street facilities to the most savvy experienced commuter who rode every single day in all types of traffic conditions. With this in mind, the extreme values noted above (1.24 and 5.49) are believed to represent the extremes that might be expected in practice. Shown in figure 15 is a line drawn between these two extreme points, which approximates the distribution of participant scores. On the lower end of the scale, the extreme value of 1.24 represents the point at which virtually all bicyclists feel comfortable riding under a given set of roadway conditions. On the upper end, the extreme value of 5.49 represents the opposite, i.e., the point at which virtually no bicyclists feel comfortable riding. In between these extremes, percentiles along the line can then be selected and used to represent the breakpoints between the various LOS designations. While the selection of these breakpoints is arbitrary (as are the breakpoints used in the Highway Capacity Manual for other LOS designations), they have been chosen to reflect the full range of site conditions and bicycling experience levels present in most urban and suburban areas.
The 50th percentile along the line corresponds to a mean overall rating of 3.40. Since there are six levels of service (A through F), the rating corresponding to the 50th percentile (3.40) was selected as the breakpoint in the middle of the scale between LOS C and LOS D (see table 13).
The breakpoints between the other levels were selected to reflect a slightly greater concentration of scores surrounding the 50th percentile and a very low concentration at the extremes. Extending 25 percent from either side of the 50th percentile results in a 75th percentile along the line corresponding to a mean overall rating of 4.40 and a 25th percentile corresponding to a value of 2.30. These values were selected as the breakpoints between LOS D and LOS E, and LOS C and LOS B, respectively.
To define the breakpoint between LOS E and LOS F, the 95th percentile was selected. From figure 15, this percentile corresponds to the mean overall rating of 5.30. On the other end of the scale, the 5th percentile was selected as the breakpoint between LOS A and LOS B, equivalent to a mean overall rating of 1.50. Note, the LOS designations were established using the BCI model for all bicyclists (see table 8). It is not appropriate to use the results from models for specific experience levels (i.e., experienced commuter vs. experienced recreational vs. casual recreational) with these LOS designations. A more complete discussion of how to use these LOS designations in cases where it is known that the majority of bicyclists using a particular route are indeed "casual" is provided in chapter 6.