BridgeStation Condition performance measures are based upon national guidance. Below is the general definition of the Key Performance Indicator reported on BridgeStation. For detailed information please refer to below guidance.
Guidance Document for Performance Measurement of Highway Structures
Part B1: Condition Performance Indicator
Report prepared on behalf of: Highways Agency, CSS Bridges Group (2007)
Bridge Condition Indicator (BCI)
The term used for the Condition PI when it was originally developed by the CSS Bridges Group.
Condition Performance Indicator (Condition PI)
The generic term used for the Condition PI. For external reporting, the Condition PI refers to the highway structure stock, but for internal management/reporting the Condition PI may be used at the structure group and individual structure level. The Condition PI is calculated on a scale of 100 (best condition) to 0 (worst condition).
Structure/Bridge Condition Score (SCS/BCS)
An average and a critical SCS score are evaluated for each structure, where:
- SCS/BCS Average – the weighted average of all the ECI scores for the structure, the ECI scores are weighted by their respective EIF. The score is on the 1 (best condition) to 5 (worst condition) scale. o
- SCS/BCS Critical – equal to the ECI of the Very High-importance element on the structure that is in the worst condition.
The score is on the 1 (best condition) to 5 (worst condition) scale.
Condition PI Average / BCI Average
The conversion of the SCS/BCS Average score to a more readily understood and presentable 100 (best condition) to 0 (worst condition) scale.
Condition PI Critical / BCI Critical
The conversion of the SCS/BCS Critical score to a more readily understood and presentable 100 (best condition) to 0 (worst condition) scale
SOGR (% Area)
LoBEG and TfL have sought to simplify the way the condition of individuals and stocks of structures are indicated and reported in all their relevant performance reports, without moving away from the principles of the established Bridge Condition Indicators methodology. It was agreed that a single number (State of Good Repair) would achieve this as a measure of condition. The following formula for the State of Good Repair (SoGR) has been defined:
A structure is considered in a State of Good Repair (SOGR) if its "BCI Combined" is >= 65.
Where, BCI Combined (SOGR Condition) = (0.6 × BCI Average) + (0.4 × BCI Critical)
SOGR (% Area) is then calculated as % of structure stock area (weighted by AVF) in a State of Good Repair (ie BCI Combined >=65).
Structures At Risk
A total number of structures with safety or performance at risk. A structure's safety or performance is considered to be at risk if at least one element with a Very High importance rating has reached or exceeded condition 4B.
Structures (IM)
A total number of structures with Interim Measures. Calculated based on the number of Very High and High importance elements that have reached or exceeded 4B.
Total IM
A total number of Interim Measures. Calculated based on the number of Very High and High importance elements that have reached or exceeded 4B.
Restrictions
A total number of restrictions. It is considered that 20% of structures with IM (Structures (IM)) will have restrictions.
Please note that "Structure IM Factor" and "IM Count Factor" bands are derived with empirical data analysis carried out by LoBEG and TFL.