Systems Planning Office
General Information on K Factor
WHAT IS K
- Selecting a proper time period is crucial for planning and designing transportation facilities. The ratio of peak hour to annual average daily traffic factor (K) is used in the Department's planning through design phases. It is one of, if not the most critical traffic considerations in the Department's efforts in planning and designing of highway facilities. Yet, in actual practice, there is considerable confusion and inconsistency in how this important traffic factor is used throughout the Department.
WHY STANDARDIZE K
- The concept of arranging hourly volumes in descending order of magnitude and the use of the 30th highest hour in relation to AADT was introduced in the 1950 Highway Capacity Manual. The term developed for the practice of converting daily volumes to the 30th highest volume became K30, commonly referred to as the "design hour". The concepts of using K30, K100, peak to daily ratios or other approaches has created much confusion throughout the state on what is the most appropriate K factor to use. During peak travel hours many Florida roadways are oversaturated or constrained: travel demand exceeds the capacity of the roadways to handle it. Using measured K factors for oversaturated roads distorts how roadways should be planned and designed. Measured volumes simply cannot exceed a roadway's capacity even during peak hours. Especially problematic is the determination of appropriate K values in large urbanized areas.
DEFINE STANDARD K
- FDOT should adopt a "design" approach in which K factors are set for roadways from planning through design. Rather than being a variable, K becomes a fixed, cost effective parameter, much like the use of 12-foot through lanes is on major high-speed roadways. The selected K factors should also reflect growth management and economic development considerations. There is not a single standard K value to be applied to every roadway in the state; rather there are multiple standard K factors depending upon the area type and facility type to be applied statewide. Values would be set primarily by the area in which roadways are located and facility type.
FDOT Recommended K Factors
Understanding Standard K Factors
Typically, K factors are calculated on a project by project basis for planning through design phases of transportation facilities. This practice characteristically causes inconsistency and confusion in the application of K factors. Experienced professionals recognized these factors derived were historically high and technically outdated. A methodical process was developed in order to obtain accurate, representative standard K factors based on area type and facility type with consideration to typical peak periods of the day. Specifically, on the freeways in the 7 largest urbanized areas in Florida, we have gone to a peak study period. For all other facilities we have gone to a peak hour not within the peak season. The recommended standard K factors developed are reflected in the adjacent table. Please note, it is recognized that adjustments will need to be applied to specialized areas like multimodal transportation districts.
Benefits of Standard K
Promotes Better Transportation
- Time savings to FDOT
- Updated latest research
Consistency: Planning through Design
- Within Department
- Throughout development community
- Simple to understand
- Positive for Development
- Supportive of Growth Management
District 4 Pilot Study
Draft Issue paper on Improving Florida's Transportation Planning and Design Analysis Time Period Process (Adopting Standard K Factors
and Level of Service Standards throughout FDOT)