Guidebook on Pedestrian and Bicycle Volume Data Collection (2014) / Chapter Skim
Currently Skimming:
Pages 57-74
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 57... ...
57 c h a p t e r 4 4.1 Chapter Overview This chapter discusses two types of factors that can be applied to raw count data: correction factors and expansion factors. Correction factors account for systematic inaccuracies in automated counter technology.
|
From page 58... ...
58 Guidebook on pedestrian and Bicycle Volume Data collection pronounced with higher volumes (i.e., errors are non-linear) (Ozbay et al.
|
From page 59... ...
adjusting count Data 59 were collected during heavy precipitation events. Anecdotal reports from active infrared sensors have suggested very high overcount rates in heavy rain and snow.
|
From page 60... ...
60 Guidebook on pedestrian and Bicycle Volume Data collection count. At higher values of AAPD, the counter is less consistent in its detection error, which means that more error will remain in the results after applying an adjustment factor.
|
From page 61... ...
adjusting count Data 61 have a much higher AAPD. Similarly, the active infrared data have a correlation coefficient extremely close to 1.
|
From page 62... ...
62 Guidebook on pedestrian and Bicycle Volume Data collection Comparison with Previous Research Previous research has primarily focused on active and passive infrared, inductive loops, and pneumatic tube sensors. Consistent definitions of error rates and data collection protocols have not been used, which makes direct comparisons difficult.
|
From page 63... ...
adjusting count Data 63 Multiplicative factors, as shown in Table 4-2, are the easiest form of correction factor to interpret and estimate. For most applications, using simple multiplicative factors is sufficient.
|
From page 64... ...
64 Guidebook on pedestrian and Bicycle Volume Data collection Possible explanations for differences between the NCHRP Project 07-19 results and previous results in the literature on environmental effects on count accuracy include (1) improvements in how vendors have implemented technology and (2)
|
From page 65... ...
adjusting count Data 65 loops that extended over most of the facility width, as well as channelization features that forced bicyclists to ride over the sensors. 4.4.2 Developing Site-Specific Correction Factors Developing a local correction factor requires conducting manual counts and comparing the results to the automated counter data.
|
From page 66... ...
66 Guidebook on pedestrian and Bicycle Volume Data collection collected) is recommended when developing correction factors.
|
From page 67... ...
adjusting count Data 67 • Land use and facility type adjustments. These adjustments can be used to account for differences in volumes attributable to differences in the surroundings of a count site, compared to a continuously counted control site.
|
From page 68... ...
68 Guidebook on pedestrian and Bicycle Volume Data collection Temporal expansion factors are simple to apply. A look-up table is generated from the permanent count data, giving the percentage of the total volume observed during each time period.
|
From page 69... ...
adjusting count Data 69 January was 44,143; and (552,592)
|
From page 70... ...
70 Guidebook on pedestrian and Bicycle Volume Data collection control site. This approach is more robust for estimating pedestrian volumes than bicycle volumes, because bicycle trips tend to be longer and more "through traffic" is counted that does not necessarily have much relation to the surrounding land use characteristics.
|
From page 71... ...
Table 4-5. Weather-related effects on non-motorized volumes documented in the literature.
|
From page 72... ...
72 Guidebook on Pedestrian and Bicycle Volume Data Collection Step 1A. Establish Site-Level Data Correction Factors Manual counts can be conducted at the study site and compared with the automated data from the counter.
|
From page 73... ...
Adjusting Count Data 73 the adjustment function, which is a mirror image of a best-fit line through the data points. Automated counts should be multiplied by the slope of the thick solid line to bring them closer to the perfect accuracy line.
|
From page 74... ...
74 Guidebook on Pedestrian and Bicycle Volume Data Collection Next, consider what could be done if only the first 8 days in October had been counted at the study site, resulting in a corrected volume of 14,031 for those days. One way to handle this would be to assume that all of the 31 days in October are roughly equal in terms of volume and expand the corrected volume by the proportion of the month it represents.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.