Impact factors were recorded on main members and deck slabs (where appropriate) of 12 bridges of between 9 and 30 metre span, under normal traffic conditions.
Correlation of impact factor was checked against span length, natural frequency, damping, support member material, end conditions and road roughness, and against vehicle speed and proportion of design load.
Significant correlation was seen only against proportion of design load. Although there was marked variation between the bridges, the variation at design load level was limited.
The conclusion was that current design criteria covered the impact factor adequately and should be retained.
Keywords: bridge, load, dynamic, impact, New Zealand, highway