Reinforced concrete decks are in most cases the fastest deteriorating components of a bridge due to the multitude of influencing factors: direct traffic loading and environmental effects, maintenance activities (salting), etc. Among many deterioration types, corrosion induced deterioration is the most common problem in reinforced concrete decks. The condition of bridge decks is predominantly evaluated through visual inspection, which can detect visible signs of deterioration. The results of visual inspection are quantitatively summarized by the NBI (National Bridge Inventory) condition rating. On the other hand, nondestructive evaluation (NDE) technologies enable detection and quantification of invisible deterioration. The assessment, most commonly, has three main components: assessment of corrosion, concrete degradation assessment, and assessment with respect to deck delamination. Four technologies are used for those purposes: electrical resistivity (ER) to estimate the corrosion rate, ground penetrating radar (GPR) to describe corrosive environment and qualitatively describe concrete deterioration, ultrasonic surface waves (USW) method to describe concrete quality, and impact echo (IE) to detect and characterize delamination. The results of NDE surveys are described in terms of condition maps and summarized in terms of condition indices with respect to corrosion, concrete quality and delamination, and the summary or combined condition index. The paper concentrates on the comparison of the NBI ratings and condition indices for a cluster of eighteen bridges that were surveyed as a part of the Federal Highway Administration's (FHWA's) Long Term Bridge Performance (LTBP) Program. The comparison of NBI ratings and NDE condition indices was conducted on both individual NDE technology level, and with respect to the combined NDE condition index. The main conclusion is that, while there is a correlation between the NBI condition rating and the average NDE condition index for the cluster, significant differences can exist on an individual bridge level.

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