A septic tank, riser or lid located anywhere a vehicle could drive or park over it, a parking lot, a driveway, a loading area, needs traffic-rated construction, commonly referenced in the industry as H-20 rated after the AASHTO loading standard, rather than the standard lightweight risers and lids used under a lawn or landscaped area.
On a typical residential lot, a septic tank and drainfield usually sit under a yard where the heaviest load is foot traffic or a lawn mower. Commercial sites are laid out around parking, loading and drive lanes, and available land for a drainfield or tank location often ends up under or near pavement, which means the tank access points, risers and lids have to be built to handle vehicle loading rather than the lighter components used residentially.
The reference point commonly used across the industry for this is AASHTO's H-20 highway loading standard, and septic tank, riser and lid manufacturers sell products specifically marketed as H-20 rated for exactly this use case.
Where possible, keeping tanks and access points out of drive lanes and parking stalls avoids the added cost and complexity of traffic-rated components entirely; where that is not possible given the site's layout, traffic-rated construction is not optional, it is what keeps the tank and its access intact under real vehicle loads.
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A new use, an addition, a remodel, a change of tenant, gets compared against what a commercial property is already permitted for. Where a recorded septic file exists for the property, it typically shows the tank size, the treatment components, the drainfield or dispersal area, and the design flow the system was approved for, which is the starting point for figuring out whether a change fits inside the existing approval or needs an upgrade. We publish where county septic records are kept and how many we hold, we list local septic companies by county, and we generate a free, code-referenced septic design for a parcel to use as a starting point.
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It refers to construction built to AASHTO's H-20 highway loading standard, the reference commonly used across the industry for septic components that will sit under vehicle traffic, as opposed to standard lightweight components used under a lawn.
Only where the tank, riser or lid is located anywhere a vehicle could drive or park over it. Components sited away from drive lanes and parking can generally use standard construction.
Sometimes, by siting the tank and access points outside drive lanes and parking areas during design; where the site layout does not allow that, traffic-rated construction is necessary.
Page last reviewed 2026-08-31.