Need More Stations?
After grouping the permanent counters by pattern, consider if additional counters would be beneficial.
1. Are there any major types of patterns not represented?
2. Is each geographic or climate region represented?
3. Would adding permanent counters to any of the factor groups improve the quality of the factors?
To answer Question 1, one might look at the patterns found at the short duration locations (you can start to see these if you have at least 12 hours of data per site). Are most of the patterns found in your short duration sites represented by permanent counters? If not, consider adding more permanent counters where these types of patterns might exist. If no short duration counts longer than 12 hours exist, consider the patterns found by others: commute, recreational, and mixed.1 Are each of these represented by your permanent counters? Are there other patterns in your community that should be represented, such as school patterns?
Answering Question 2 might require little more than mapping the locations and overlaying the climate and geography of the study area. Is each major climatic zone or geographic area that is likely to impact cycling and walking behavior represented?
To answer Question 3, the Traffic Monitoring Guide provides guidance that generally – for motorized traffic – five to eight permanent counters are needed per factor group. Since bicycle and pedestrian traffic is more variable, more counters might be required to compute reliable factors. While further research is needed to answer this question, research conducted in Colorado recommends at least seven permanent count stations per factor group.2
A graph from the 2013 Colorado Department of Transportation report is reproduced below showing the normalized precision interval of the monthly factors for various numbers of counters. The Traffic Monitoring Guide recommends analyzing the precision of the factors in order to judge the grouping of counters. The smaller the normalized interval, the tighter the precision. The average precision interval shown for the Colorado bicycle count data seems to suggest that to achieve reasonably accurate factors at least seven continuous counters per factor group are needed.
Source: Colorado Department of Transportation.
4.4.4 STEP 5: DETERMINE APPROPRIATE NUMBER OF CONTINUOUS MONITORING LOCATIONS
Very little is known about spatiotemporal variation of non-motorized traffic, and what is known is very location-specific and difficult to generalize nationwide. In most cases (where no non-motorized counting currently exists), the number of count locations will be based on what is feasible given existing traffic monitoring budgets.
1Turner, S., Qu, T., & Lasley, P. (2012). Strategic Plan for Non-Motorized Traffic Monitoring in Colorado (pp. 99). College Station, TX: Texas Transportation Institute.
2Nordback, K., Marshall, W. E., & Janson, B. N. (2013). Development of Estimation Methodology for Bicycle and Pedestrian Volumes Based on Existing Counts (pp. 157). Denver, CO: Colorado Department of Transportation (CDOT).