Curious to see what the values the various states use.
Arkansas
Considered congested above
* Rural two lane: 9,000 ADT
* Urban two lane: 13,000 ADT
* Four lane freeway: 50,000 VPD
* Six lane freeway: 80,000 VPD
Source: http://www.arkansashighways.com/stip/2006_Needs_Study_Highway_Improvement_Plan.pdf (http://www.arkansashighways.com/stip/2006_Needs_Study_Highway_Improvement_Plan.pdf) (Page 19/73)
Iowa DOT
* Seems to be capacity of two lane road: 6,000 VPD
* Two lanes plus Two Way Left Turn Lane: 15,000 to 17,500 ADT
http://www.iowadot.gov/design/dmanual/06c-06.pdf (http://www.iowadot.gov/design/dmanual/06c-06.pdf)
Florida? (Not sure; see Page 50 of http://www.franklinmo.org/Highway_Department/Franklin_Co_long_range_transportationplan.pdf (http://www.franklinmo.org/Highway_Department/Franklin_Co_long_range_transportationplan.pdf)
Also see http://www.dot.state.fl.us/planning/systems/sm/los/pdfs/2009FDOTQLOS_Handbook.pdf (http://www.dot.state.fl.us/planning/systems/sm/los/pdfs/2009FDOTQLOS_Handbook.pdf)
For Level of Service E:
* Two lane undivided signalized: 16,600 ADT
* Four lane undivided signalized: 33,350 ADT
* Four lane divided signalized: 35,100 ADT
* Six lane divided signalized: 52,350 ADT
* Eight lane divided signalized: 67,400
* Two lane uninterrupted undivided: 27,000
* Four lane uninterrupted divided: 75,550
* Six lane uninterrupted divided: 117,750
* Eight lane uninterrupted divided: 159,950
* Ten lane uninterrupted divided: 202,000
* Twelve lane uninterrupted divided: 244,150
The engineering company Kimley-Horn uses Table 8 from the 2009 FDOT QLOS Handbook to evaluate roadway capacities, even outside of Florida.
Example: Appendix A of a traffic impact fee study in Monterey County, CA:
http://www.tamcmonterey.org/programs/devimpfee/pdf/2008-0326_TAMC_Nexus_Study_Update.pdf
The traditional Caltrans rule of thumb (cf. Newman's primer on highway capacity back in the 1960's) was LOS D in urban areas, and LOS B in rural areas. Both were measured in relation to facility type, taking DHV as the volume corresponding to the thirtieth highest (most-trafficked) hour in the design year.