Track faults don’t begin at the surface. Let’s look at what’s happening underneath.
While rough ride alerts and track geometry exceptions are standard in rail condition monitoring, they are often treated as symptoms rather than diagnostic clues.
By combining in-service ride quality data with ground penetrating radar (GPR), we can go a step further — using these alerts to uncover why problems occur beneath the surface.
Turning vibration into insight
In this example, bogie- and body-mounted Inertial Measurement Units (IMUs) were used to record vertical acceleration, cyclic top, and alignment — all indicators of ride quality. These were collected in parallel with GPR data, which captured subsurface details of the ballast condition and subgrade support.
The combined data gives us a powerful toolkit for root cause analysis — correlating ride experience with trackbed condition and identifying where intervention is needed.
From network view to local insight
At the network scale, we compared GPR-derived ballast fouling against vertical ride comfort. The correlation revealed hotspots where ballast or subgrade conditions aligned with rough ride indicators.
Figure: Network scale GPR-derived ballast fouling (left) and vertical ride comfort (right).
Zooming into local areas tells a more specific story:
- Case 1: Poor ride comfort was linked to shallow, fouled ballast, mudspot development, and high moisture content — all clearly visible in the GPR data.
- Case 2: A rough ride was observed despite deep, clean ballast. GPR revealed a subgrade degradation spot, strongly suggesting that the issue lay in a lack of formation support.
Figure: Zoomed in view of GPR-derived ballast fouling levels and rough ride indications with areas of interest labelled.
In both cases, the GPR plots didn’t just confirm the ride quality data — they helped explained it.
Diagnostic power of GPR
GPR radargrams (down to ~1.2 m depth) provided visual confirmation of subsurface issues:
- Layer boundaries and fouling depths
- Areas of retained water or mud
- Loss of subgrade integrity
Figure: GPR radargram (showing an ~ 1.2 m depth window) with different rough ride causation attributes for the two cases.
This helps teams to differentiate between surface and structural problems — and avoid unnecessary ballast cleaning or misdirected maintenance.
Takeaway
Rough ride alerts shouldn’t just trigger more inspections — they should trigger smarter, targeted diagnostics.
By linking ride experience with what’s happening beneath the track, we can shift from reactive to predictive maintenance.