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50 Supplemental Grade Study During the process of developing guidelines for bike lane widths under various conditions, it was desirable to under- stand how roadway grade affects cyclist position. Specifically, the question of how much a cyclist drifts and sways back and forth while pedaling up a moderate to steep grade was of interest. Understanding the operating characteristics of cyclists pedaling up hills is important in determining whether wider bicycle lanes may be appropriate on upgrades. 4.1 Description of Field Study A small study was conducted near the MRIGlobal campus in Kansas City, Missouri, in which six volunteers (four males and two females) rode their bicycles up a moderate grade. The volunteers were recruited from the MRIGlobal staff and were not members of the Transportation Research Center to avoid any potential bias. They ranged in skills from regular commuters to those who bicycle only recreationally. The par- ticipants used their own bicycles (from high-end road to inex- pensive mountain bikes) during the study. Table 18 specifies the age and skill level of each participant and type of bicycle used during the testing. A low-volume roadway with an upgrade of 3% to 4% was selected for the study. A temporary 4-in. longitudinal line was painted on the roadway surface 5 ft from the edge of the curb face, beginning approximately 80 ft from the bottom of the hill and extending for 60 ft along the roadway. A video camera was positioned downstream of the study section to record cyclists traversing the 60-ft section. Reference markings were placed at 10-ft increments along the study section, permitting six measurements of cyclist lateral position per rider travers- ing the section once. One at a time, cyclists started from the bottom of the grade and pedaled up to and through the 60-ft study section. Each cyclist completed the course five times. The roadway was not closed for the study. Participants were directed to bicycle up the grade within the bike lane as they naturally would. Figure 32 shows video frames of a bicy- clist traversing the study section as part of the supplemental grade study. Following the field study, the video recordings were viewed to document the lateral position (relative to the curb) of each cyclist at 10-ft increments along the study section. Thus, a database of 180 records of lateral position (6 riders à 5 tra- versals à 6 measurements of lateral positioning) was assem- bled. From the lateral position of each cyclist relative to the curb at the six locations along the study section, two variables were derived to capture the cyclistsâ sway and drift along the section of road. The two indicators are defined and their esti- mates provided in the following. 4.2 Data Analysis Six measurements of lateral position were taken over a 60-ft section of the upgrade roadway for each rider during each run. From these, sway and deviation from a straight-line trajectory were defined as follows: ⢠Sway: For each rider and run, sway was calculated as the difference between the maximum and minimum of the six lateral positions from the curb. ⢠Deviation from a straight-line trajectory: For each rider and run, a straight-line trajectory was defined by the line connecting the lateral position at the first and last reference markings. The deviations at marking numbers 2 through 5 from that line were then calculated and averaged. The distribution of sway is shown separately for each cyclist in Figure 33, and the distribution of deviation from a straight- line trajectory is shown separately for each cyclist in Figure 34. Basic descriptive statistics (minimum and maximum, mean, median, and standard deviation) for each indicator are shown at the bottom of each box plot. The horizontal lines in each S E C T I O N 4
51 Figure 32. Video frames of a bicyclist traversing the upgrade during the supplemental grade study. Participant Age Skill Level Bike Type 1 44 Moderate Hybrid 2 66 High Road 3 28 Moderate Road 4 70 Low Mountain 5 34 High Cruiser 6 30 Moderate Mountain Table 18. Descriptives of supplemental grade study participants.
Horizontal dashed lines represent overall 5th, 50th, and 95th percentile sway (2.9 in.; 6.4 in.; and 9.3 in.) White dot = mean; Star = extreme value; Gray box = mid 50% of data 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 Sw ay (i n) Rider No. N 5 Min 3.0 Mean 4.6 Median 4.5 Max 7.3 Std Dev 1.66 5 3.6 6.0 5.9 9.1 2.31 5 5.2 7.6 7.7 9.3 1.52 5 2.9 6.4 7.5 9.9 2.83 5 2.0 5.4 6.8 7.7 2.43 5 3.5 5.8 5.6 7.7 1.58 Figure 33. Distribution of cyclistsâ sway. Horizontal dashed lines represent overall 5th, 50th, and 95th percentile deviation from straight-line trajectory (-3.2 in., -0.6 in., and 3.6 in.) White dot = mean; Star = extreme value; Gray box = mid 50% of data 1 2 3 4 5 6 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 )ni( yrotcejart enil-thgiarts morf noitaiveD Rider No. N 20 Min -3.8 Mean -0.7 Median -0.9 Max 4.2 Std Dev 1.95 20 -3.8 1.3 1.4 8.1 2.63 20 -6.9 0.7 0.8 7.8 3.51 19 -6.5 -0.7 -1.1 4.9 2.65 20 -4.3 -1.4 -1.2 1.1 1.56 20 -5.4 -1.1 -1.2 4.3 2.54 Figure 34. Distribution of cyclistsâ deviation from straight-line trajectory.
53 box plot mark the 5th, 50th (median), and 95th percentiles. Thus 90% of the sway measurements fall between 2.9 and 9.3 in.; 90% of the deviations from straight-line trajectory fall between â3.2 and 3.6 in. Overall mean estimates and 95% confidence intervals of both indicators were calculated, taking into account rider variability; the results for each are as follows: ⢠Average back-and-forth sway was 6 in., with a 95% con- fidence interval of 4.9 to 7.1 in. ⢠Average deviation from a straight-line trajectory was -0.3 in., with a 95% confidence interval of -1.4 to 0.81 in. 4.3 Summary of Key Findings The primary findings from the supplement grade study con- ducted to understand the operating characteristics of cyclists on a moderate to steep upgrade are summarized as follows: ⢠Cyclists do sway back and forth while pedaling up moder- ate to steep grades. ⢠There is considerable variability in the amount of sway among riders. ⢠The largest observed deviation from a given straight-line trajectory was approximately 8 in., but generally, cyclists deviated only 3 to 4 in. from their straight-line trajectory.
