GUIDANCE FROM THE TRAFFIC MONITORING GUIDE 2013, SECTION 4.5.5
4.5.5 FACTORING SHORT-DURATION COUNTS
As indicated in the previous section, a factoring process may be necessary to adjust short-duration counts to best represent an annualized estimate. The factoring process for motorized traffic has been described in depth in Chapter 3. It is recommended that a similar factoring process be used to annualize non-motorized traffic counts.
Depending on the count duration, type of automated equipment used, and presence of inclement weather, there may be up to five factors that could be applied:
6. Time-of-day: If less than a full day of data is collected, this factor adjusts a sub-daily count to a total daily count.
7. DOW: If data is collected on a single weekday or weekend day, this factor adjusts a single daily count to an average daily weekday count, weekend count, or day of week count.
8. Month/season-of-year: If less than a full year of data is collected, this factor adjusts an average daily count to an annual average daily count.
9. Occlusion: If certain types of automatic counter equipment are used, this factor adjusts for occlusion that occurs when pedestrian or cyclists passing the detection zone at the same time (i.e., side-by-side or passing from different directions).
10. Weather: If short-duration counts are collected during periods of inclement weather, this factor adjusts an inclement weather count to an average, typical count.
Adjustment factors are developed for distinct factor groups, which are groups of continuous counters that have similar traffic patterns. The continuous counters in the factor groups provide year-round non-motorized traffic counts and permit these short-duration counts to be annualized in a way that minimize error.
The non-motorized data submittal formats in Chapter 7 provide the capability to report these five types of adjustment factors in five separate factor groups.
Although factoring is a straightforward mathematical process, very few agencies are using factor groups for non-motorized traffic counts. There is no consensus yet on several aspects of the factoring process, such as the required type of factor adjustments, the number of factor groups for each adjustment type, and the number of continuous count locations within each factor group. It is hoped that future editions of the Guide will be able to provide additional guidance on this non-motorized count factoring process.
Many State DOTs do have data warehouse tools that already perform the factoring process for motorized traffic counts. Many of these tools and factoring processes could be used for non-motorized traffic factoring, given some adaptation as discussed in this section.