Structural identification (St-Id) of long-span bridges by ambient vibration testing provides a starting point for quantitatively characterizing the actual in-service mechanical characteristics and behaviours of these complex constructed systems.However, various uncertainties involved in the experimental and identification processes impact the reliability of St-Id especially if vibration testing is the sole experiment.Such uncertainties represent perhaps the most fundamental barri er to more widespread applications of measurements in civil engineering practice.The goal of this paper is to leverage a vi bration test of a long-span suspension bridge to illustrate a number of possible strategies for coping with the uncertainties confronted when identifying the dynamic characteristics of large-scale constructed systems.The design and implementation of a field test in the context of St-Id are first presented to illustrate how uncertainties can be mitigated by following a disci plined approach to designing the experiment.Next, data pre-processing strategies including data inspection, time window selection, band-pass filtering, averaging and windowing are proposed to reduce data errors.Three separate post-processing methods, including Peak-Picking, PolyMAX, and Complex Mode Indicator Function (CMIF), are executed independently tO verify the reliability of the data processing results.Experimental results for both the towers and suspended spans are cor related with the simulations from 3D finite element analysis of the long span bridge for St-Ic.