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TrafLoad uses TOD traffic ratios to convert partial-day classification counts to estimates of vol- ume by VC for the day on which the count is collected. These traffic ratios generally are devel- oped from hourly classification counts obtained for weekdays at Level 1A sites, as discussed in Section 3.3. For this purpose, each Level 2B site must be assigned to a TOD factor group that is believed to have a TOD pattern for truck volume (particularly for combination trucks) that is similar to the pattern that is believed to exist at the site in question. A separate set of TOD traffic ratios is used for each Type 1 VC group. For Level 2B sites, TrafLoad also produces a set of monthly traffic distribution factors and, at user option, it may produce a set of hourly distribution factors. As in the case of Level 2A sites, the monthly traffic distribution factors for each Level 2B site are equal to the monthly traffic ratios for the seasonal factor group to which the site has been assigned. For sites identified by the user as ones at which a business-day truck pattern exists, TrafLoad produces a set of hourly distribution factors that have the values shown in Table 3.2. For all other Level 2B sites, TrafLoad does not produce any hourly distribution factors. Instead, the Pavement Design Guide software provides its default TOD distribution.7 3.5 Level 3 Classification Sites Level 3 classification sites are sites for which volume counts exist but classification counts do not exist. There are two types of Level 3 classification site: · Level 3A sites are sites on the same road as an associated Level 1 or Level 2 site and suffi- ciently close to that site to carry a traffic mix that is similar to the mix at the associated site. · Level 3B sites are all other sites. For both types of Level 3 site, TrafLoad requires either an estimate of overall (two-way) annual average daily truck traffic (AADTT) or estimates of overall AADT and overall percent trucks from which AADTT can be derived. Level 3A Sites Level 3A classification sites are sites that are on the same road as an associated Level 1 or Level 2 site and sufficiently close to that site to carry a traffic mix that is similar to the mix at the associated site. For such sites, TrafLoad uses the estimates of AADTi by direction at the associated site to distribute the user-supplied estimate of AADTT over the various truck 7 There is a relationship between the hourly distribution factors (HDFs) required by the Pavement Design Guide software and the TOD traffic ratios (TODTRs) developed and used by TrafLoad. How- ever, the Pavement Design Guide software requires a single set of HDFs for all VCs combined, while TrafLoad generates separate sets of TODTRs for each VC group. The current version of TrafLoad does not contain a procedure for converting the TODTRs into HDFs. 2-37
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Table 3.2 Hourly Distribution Factors Used by TrafLoad for Level 2B Sites with Business-Day Trucking Hour Hourly Distribution Factor 0 0.6% 1 0.4% 2 0.4% 3 0.4% 4 0.9% 5 2.8% 6 4.8% 7 6.1% 8 7.4% 9 7.8% 10 7.7% 11 7.6% 12 7.5% 13 7.9% 14 8.0% 15 7.0% 16 5.9% 17 4.7% 18 3.6% 19 2.6% 20 1.9% 21 1.6% 22 1.3% 23 1.1% Derived from data for urban other principal arte- rials (Functional System 14) in Mark Hallenbeck, et al., Vehicle Volume Distributions by Classification, Chaparral Systems Corporation and Washington State Transportation Center, June 1997, for FHWA, FHWA-PL-97-025, pp. 79-80. 2-38