Over 90% of tracks around the world are ballasted.
The essential functions of a ballasted trackbed are to:
- Transfer loads from sleepers to the subgrade
- Restrain the track
- Provide adequate drainage
- Maintain proper track geometry
To ensure ballast is fit for purpose, and assuming 30cm of track below the base of sleepers you will need about 3,400 tons per mile to build or renew track, about 1,500 tons to undercut (ballast clean) a mile of track assuming 40% of ballast is wasted, and about 1,000 tons to surface / lift a mile of track by 10cm.
The cost to source ballast and deliver to site is from $20-$60 per ton depending on many parameters. For simplicity let’s use $40/ton which equates to a per mile material cost alone of $136,000, $58,000 and $38,000 for each of the maintenance types respectively. This excludes the cost of manpower and machinery for each of these maintenance activities.
There is no one size fits all (railroads) but if you surface every two years, ballast clean every 10 years and renew ballast every 20 years, these figures equate to an annualized cost of ballast (ignoring inflation) of $32,000 per mile. If your network is 1,000 miles that’s $32M.
In the absence of evidence of actual ballast condition it would be safe to say that your ballast maintenance program might include track that doesn’t actually need maintenance – we would suggest about 10% to be kind, which would equate to $3,200 per mile of misspent budget.
Which leads neatly on to the answer to the question “Why bother inspecting ballast?”
One good reason (others will be discussed in following blogs) is because non-invasive inspection of your ballast every year can be achieved for an annualized data processing cost of a few hundred $ per mile which could lead to a potential saving of $3,000 per mile (in round terms), or $3M for a 1,000 mile network, in reduced ballast material spend.
The game changer is contextualised ground penetrating radar (GPR) information. This means GPR-derived below ground trackbed quality information used in conjunction with track geometry and other information like lidar (for surface ballast volume measurements), to provide a cost effective ballast maintenance plan.
If you’re interested to learn more about how this works take a look at this explainer video.
Stay tuned to our blog series on the benefits of railway asset condition mapping.