Bridge Defect Investigations Expert Overview

The engineers at Robson Forensic are often retained in cases involving bridges: structural failures and collapse, vehicle crashes, pedestrian strikes, construction claims, and a multitude of other disputes that can result in litigation. This article focuses on the aspects of bridge safety that are most relevant to motor vehicle and pedestrian safety.

Investigating Bridge Defects

Federal law requires inspections at least every 2 years on all public highway bridges over twenty feet long. These inspections must comply with the National Bridge Inspection Standards (NBIS) and must be led by a Certified Bridge Safety Inspector (CBSI).

The Federal Highway Administration monitors inspections to ensure compliance with National Bridge inspection Standards (NBIS). Inspection requirements can differ from state to state in addition to variations among county and municipal owners within each state.

Bridge Safety Features

In many respects, bridges are a microcosm of the larger transportation system. Modern bridges contain the same design elements for positive vehicle guidance, crash attenuation, and pedestrian safeguarding as one would encounter in contemporary roadway projects.

Well-designed bridge features reduce exposure to dangerous conditions and increase public safety. Therefore, inspectors are tasked with identifying and reporting noteworthy conditions regarding:

1. Pavement surfaces: drop-offs, potholes, ruts, bumps, and/or excessive cracking
2. Drainage features: scuppers, inlets, and piping
3. Traffic control devices: signage, lane striping, traffic signals, rumble strips, reflective delineators
4. Bridge joints & barrier elements: bridge parapets, transitions, guide rails, end treatments, medians, curbs, and fencing

The following images demonstrate some of the conditions that bridge inspectors observe which potentially relate to public safety.

Bridge Inspection Expert Observations

In this image, the approach pavement (roadway leading up to the bridge) is on the left, and the bridge deck (roadway of the bridge) is on the right.

Approach pavement is typically asphalt constructed atop earth and layers of compacted stone. Conversely, bridge decks are usually concrete built upon precast girders with steel reinforcement.

The structural difference in these abutting surfaces will often cause approach pavements to settle, leading to bumps and other surface defects. In that respect, this bridge is typical.

The bridge joint is where the approach roadway meets the bridge deck and is one of the more vulnerable areas due to the difference in structural support beneath either side.

This image shows both deterioration (potholes) and repairs (patches). There are multiple patches visible, using different fill materials.

Asphalt patching signals that the bridge deck is reaching the end of its lifespan since it is permeable, which can accelerate degradation via corrosion or seasonal freeze/thaw cycles. While the presence of a patch does not necessarily raise any red flags, the presence of multiple patches may indicate a progression of deterioration.

The paint on this bridge is deteriorating as a result of pothole formations (white striping) and from age (faded yellow paint). New pavement markings will often require that the existing markings be covered with contrasting colors (covered in black and repainted) to eliminate “ghost markings” and ensure that the new paint is highly visible to help direct traffic.

Here we see an alternate view, looking from the approach pavement towards the bridge deck.

Focusing on the drainage grate, there is visible damage to the edge from a snowplow strike. Cyclists can lose control if they hit a bump along the pavement or get their wheel stuck in a drainage grate.

The presence of unprotected barrier ends, lacking any impact attenuating treatment or guiderail, indicates that this is an older bridge. Various methods of bridge end protection are available to decrease the severity of motor vehicle impacts and would be expected on new installations. 

The image above gives an alternate view of the bridge barrier, fencing, and sidewalk. Sidewalk settlement along the bridge joint transition here has resulted in an uneven transition, creating a hazardous condition for pedestrians.

Some bridges, like this one, that go over an interstate have protective fencing to limit rocks and other objects from being dropped or thrown on to vehicles below.

Where the fence was installed atop an existing barrier (labeled Fence to Barrier Connection), the fastener and plate edges present a snagging hazard.

Other potential hazards include broken elements on the chain link fences as fence openings over fast-moving traffic below that may allow falling objects to shatter windshields and injure motorists.

Documentation of Bridge Conditions & Timeline for Remediation

Inspectors document deteriorated conditions and track them to ensure they are fixed in a timely way. The following items are generally considered critical:

• Detached pedestrian railing
• Hazardous sidewalk or deck conditions
• Loose, sharp or severely deteriorated expansion joints
• Missing clearance signs
• Severely deteriorated expansion joints
• Traffic obstructions (detached metallic railing near traffic)
• Concrete that may fall on vehicles and/or pedestrians

While these items will not cause bridge collapses, they are to be addressed to limit danger and liability.

Bridge Engineering Expert Investigations

Robson Forensic boasts a team of structural engineers, civil engineers, construction safety experts, and accident reconstructionists well positioned to conduct forensic investigations of structural failures, vehicle crashes, and construction disputes related to bridges and roadway infrastructure.

To discuss your case with an expert, submit an inquiry or call us at 800.813.6736.