A detectable warning at a transit platform edge is a 24-inch deep truncated dome surface running the full length of any platform with vehicular drop-off, set 0 to 8 inches from the platform edge. ADA Standards 810.5.2 controls the placement at transit boarding platforms, with ADA 705.1 governing dome geometry and ADA 705.2 governing visual contrast. Bus stops, light-rail stations, and ferry terminal platforms all fall under this requirement.
This guide covers platform-edge placement specifically, where the requirements differ meaningfully from a sidewalk curb-cut application.
What Does ADA 810.5.2 Actually Require?
ADA Standards for Accessible Design, Section 810.5.2, addresses detectable warnings at boarding platforms used by buses, light-rail, commuter rail, and ferries. The federal text reads "Platform boarding edges not protected by platform screens or guards shall have detectable warnings complying with 705 along the full length of the public use area."
The cross-reference to ADA 705 brings in 705.1 dome geometry and 705.2 visual contrast. ADA 810.5.2 itself adds three platform-specific placement rules.
Full length of the public-use area
The dome surface runs the entire length of the platform that pedestrians use to board or disembark. This is different from a curb cut where the dome surface is local to the ramp; on a transit platform the dome surface can run hundreds of feet.
24-inch minimum depth
The same 24-inch depth as ADA 705.3, measured perpendicular to the platform edge.
Setback from the platform edge
ADA 810.5.2 allows the leading edge of the dome surface to sit 0 to 8 inches from the actual platform edge. The setback exists to protect the dome surface from being struck by transit vehicles approaching the platform. Most transit agencies set back 6 inches; some set back 8.
Where ADA 810.5.2 Applies
The standard applies to any boarding platform with vehicular drop-off, including:
| Platform type | Application |
|---|---|
| Bus stop with raised curb | Yes |
| Bus stop at street level | Generally not (no vertical drop) |
| Light-rail platform | Yes |
| Commuter-rail platform | Yes |
| Streetcar platform | Yes |
| Subway platform | Yes |
| Ferry terminal platform | Yes |
| Airport jet bridge transition | Special rules under 810.5 |
| Curbside taxi stand | No |
Placement Geometry
The dome surface placement at a platform edge is geometrically simpler than at a curb cut because the platform edge is a single straight or curved line rather than a 5-component ramp.
Perpendicular distance from edge
Leading edge of the dome surface is at 0 to 8 inches from the platform edge. Most transit agencies standardize on 6 inches.
Depth into the platform
24 inches minimum, measured perpendicular to the platform edge.
Length along the platform
Full length of the public-use area. This typically corresponds to the area where the train or bus can stop and discharge passengers, which for light-rail is often the full length of the platform and for buses is often a 50 to 100 foot zone.
Curved platforms
A curved platform edge requires the dome surface to follow the curve, which means custom-cut panels or a mat that conforms to the curve. The 24-inch depth is measured perpendicular to the local tangent of the curve.
How Bus, Light-Rail, and Ferry Differ
The three transit modes have different platform geometries that affect placement.
Bus
Most bus platforms are 30 to 50 feet long with a curb height of 6 to 14 inches. The dome surface runs the full platform length. TriMet, Lane Transit, and Cherriots use either replaceable cast-iron systems or polymer-concrete panels.
Light-rail and commuter-rail
Rail platforms are 100 to 400 feet long with a curb height of 0 to 8 inches above the rail. The dome surface runs the full platform length, often in 24-inch by 36-inch or 36-inch by 60-inch panel modules. TriMet MAX platforms use cast-iron systems.
Ferry
Ferry platforms have a unique consideration: the platform edge is the loading transition to the vessel, which moves with tides and water level. The dome surface goes at the fixed-platform edge with the same 24-inch depth and 0 to 8 inch setback.
Common Errors at Platform Edges
These are the placement and product errors Cojo crews see at transit-platform retrofits.
Setback exceeds 8 inches
A panel installed 12 inches back from the platform edge fails ADA 810.5.2 because the setback exceeds the 8-inch maximum. Common cause: the platform itself was poured deeper than the original design intended, leaving a flat zone between the platform edge and the panel.
Length does not run full public-use area
A 50-foot dome strip on a 75-foot bus platform fails ADA 810.5.2 length. The dome surface must extend the full public-use area, which typically corresponds to where the bus or train physically stops to discharge passengers.
Composite panel on a high-traffic rail platform
A composite plastic panel installed on a busy rail platform (TriMet MAX, Sounder commuter) wears below ADA 705.5 within 5 to 7 years. Cast-iron systems are the durability spec for high-traffic transit platforms.
Material mismatch at expansion joints
Long platform-edge runs cross expansion joints in the platform itself. Dome systems must accommodate the joint movement, either with discrete panel modules or with a mat that includes joint-compatible adhesive. Continuous-pour stamped overlays can crack at the joint.
LRV differential below 70 against the platform surface
Concrete platform surfaces sometimes weather to LRV 50 to 65, which can drop the differential against a federal-yellow dome below 70. LRV verification on the actual platform surface is required, not just the manufacturer's spec.
Compliance Disclaimer
This article reflects ADA Standards for Accessible Design as of 2026-05-07 and product spec sheets current at publication. Always verify current dimensions, contrast thresholds, and placement requirements with your local jurisdiction and the U.S. Access Board before issuing a final spec. Federal guidance under 36 CFR Part 1191 controls when state or local rules conflict. Transit-agency-specific Trade Standards may layer additional requirements on top of ADA 810.5.2.
Sources
- ADA Standards for Accessible Design, Section 810.5 Boarding Platforms, U.S. Access Board, https://www.access-board.gov/ada/
- ADA Standards for Accessible Design, Section 705 Detectable Warnings, U.S. Access Board, https://www.access-board.gov/ada/
- 36 CFR Part 1191, Americans with Disabilities Act Accessibility Guidelines, https://www.ecfr.gov/current/title-36/chapter-XI/part-1191
- FHWA Accessibility Resource Library, https://highways.dot.gov/civil-rights/programs/ada/accessibility-resource-library
- Oregon Department of Transportation, ADA Curb Ramp Design Guide, https://www.oregon.gov/odot/engineering/pages/ada.aspx
From Cojo's Crew
On a Portland TriMet bus platform retrofit in February 2026 we replaced 14 cast-iron dome panels along a 60-foot platform edge after the original 1998 panels reached year-28 wear and lost contrast at the leading edge. The new replaceable cast-iron plates installed in 35 minutes per panel because the original frames remained sound. Total project ran roughly 9 crew-hours including the LRV verification on the new plates against the weathered platform concrete. Differential read 76 LRV new plate to 18 LRV concrete, well above the 70-point threshold. Replaceable systems pay off on multi-decade transit assets.