Truncated Domes
Truncated Domes for Transit Station Platforms (2026 Guide)
Cojo
May 7, 2026
7 min read
A transit station platform is the highest-stakes truncated dome environment. Bus, light-rail, and commuter-rail platforms carry tens of thousands of riders daily, expose dome surfaces to heavy mechanical and weather load, and answer to ADA Standards 810.5.2 — a stricter placement spec than the 705.3 curb-ramp rule. This guide covers the platform-edge dome product layer for Oregon transit-adjacent installations, including TriMet, Lane Transit District (LTD), Salem-Keizer Transit (Cherriots), and Rogue Valley Transportation District (RVTD) project coordination.
For the broader product comparison, see our truncated domes guide.
> Compliance disclaimer: Always verify current detectable warning requirements with your local jurisdiction and transit agency. This article reflects 2026 federal ADA Standards (28 CFR Part 36, Appendix B), ADA Accessibility Guidelines 810, and FTA accessibility guidance. Transit-agency standards may exceed federal minimums.
ADA Standards 810.5.2 covers detectable warnings at transit boarding platform edges. The rule:
This is stricter than ADA 705.3 (the curb-ramp rule). At a curb ramp, the dome field is 24 inch depth across the ramp width. At a transit platform, the dome field runs the full length of every platform edge — often 60 to 200 linear feet on a typical bus stop or 300+ linear feet on a light-rail station.
A bus or rail vehicle approaches at speeds and momentum that make a missed-edge fall a survivable-injury at best, fatal at worst. The 810.5.2 spec exists because the consequence of a vision-impaired rider stepping off the platform is severe. The U.S. Access Board's Chapter 8 Special Rooms, Spaces, and Elements covers transit platforms in detail.
| Spec point | Bus stop platform | Light rail platform |
|---|---|---|
| Depth from edge | 24 in min | 24 in min |
| Full-length requirement | Yes | Yes |
| Height tolerance vs platform | 0 in (flush) | 0 in (flush) |
| Snow / freeze-thaw exposure | Heavy | Heavy |
| Mechanical impact (cleaning) | Moderate | Heavy (sweepers, salt) |
| Recommended product | Cast-iron embedded or composite | Cast-iron embedded |
Industry Baseline Range
| Item | Range |
|---|---|
| Surface-applied composite panel (24 in by 48 in) | $260 to $480 |
| Cast-in-place composite panel (per panel) | $380 to $720 |
| Cast-iron embedded panel (per panel) | $620 to $1,200 |
| Linear foot of platform edge (composite) | $90 to $180 |
| Linear foot of platform edge (cast-iron) | $200 to $380 |
| Full bus-stop retrofit (60 lf typical) | $5,400 to $11,000 |
| Full light-rail platform (300 lf typical) | $60,000 to $115,000 |
Cast-iron panels run a 60 to 90 percent premium over composite but justify the cost on transit platforms by deferring replacement cycles. Composite panel material costs lifted 12 to 18 percent in late 2025; cast-iron pricing was steady because foundry capacity is the bottleneck not feedstock. Lead times on cast-iron run 6 to 14 weeks; plan ahead.
Each Oregon transit agency has its own coordination workflow:
Lead times for transit-platform work run 8 to 16 weeks from initial contact to install date because the platforms must remain in service during the work, requiring night-shift or off-peak scheduling.
| Application | Recommended | Reason |
|---|---|---|
| Low-volume bus stop (under 100 riders/day) | Surface-applied composite | Lifecycle cost matches usage |
| Mid-volume bus stop (100-500 riders/day) | Cast-in-place composite | Lifespan matches station capital cycle |
| High-volume bus stop (500+ riders/day) | Cast-iron embedded | Durability under cleaning load |
| Light-rail platform | Cast-iron embedded | Mechanical sweeper exposure |
| Commuter-rail platform | Cast-iron embedded | Salt exposure, freeze-thaw |
| Heritage / historic district | Custom-color composite | Aesthetic match |
Snow regions like Bend, Hood River, and high-elevation routes face two failure modes:
For Cherriots stops in the Cascade foothills and Cascades East Transit (CET) stops in central Oregon, the spec defaults to cast-iron embedded with an annual freeze-thaw inspection.
Transit platforms typically use safety yellow (RAL 1023) panels because the platform surface is usually a medium-to-dark concrete (LRV 18 to 30) and yellow (LRV 72 to 78) reliably hits the 70 percent ADA 705.2 contrast threshold. For platforms with light-colored stamped concrete or polished granite (LRV 50+), brick red (LRV 12 to 18) is the alternate choice.
| Inspection cadence | Trigger | Action |
|---|---|---|
| Quarterly | Platform sweep | Visual check for damage |
| Annually | Pre-winter | Full ADA 705 verification |
| Every 5 years | Mid-life | LRV contrast measurement |
| Every 10-15 years | Composite panels | Replacement |
| Every 25 years | Cast-iron panels | Inspection, possible insert swap |
On a 2026 ADA upgrade for a TriMet bus stop along a Sandy Boulevard route, Cojo replaced 90 linear feet of platform-edge detectable warnings. The original surface-applied composite panels (installed 2014) had developed edge-lift after 12 winters. We removed the failed panels, ground the existing concrete to bonding profile, and set new cast-in-place composite panels in a 4-inch overlay slab. The retrofit window was a Sunday-night through Monday-morning closure with TriMet rerouting service. Total panel material was 30 panels; total project cost ran near the upper end of the bus-stop baseline range due to the night-shift premium and the overlay-slab pour.
For a Portland service-area inquiry, see Portland truncated dome installation.
ADA 810.5.2 requires the full platform length. Inspectors flag any gap at the platform end where domes stop 6 inches before the actual edge. Fix: extend the field with matching panels or accept an audit failure.
Rotary sweepers running at high RPM crack composite domes. Fix: spec cast-iron at any platform with mechanical sweeper service.
Polyurethane sealant at panel perimeters fails after 5 to 8 years; water under the panel triggers freeze-thaw lift. Fix: re-seal joints every 5 years as part of standard maintenance.
UV exposure drops dome LRV. Cast-iron panels with replaceable colored inserts are the long-life answer. Fix: spec UV-stable formulations or accept a 8-to-12-year replacement cycle.
Cojo coordinates with TriMet, Lane Transit District, Salem-Keizer Transit (Cherriots), and Rogue Valley Transportation District on platform-edge truncated dome installation and retrofit work. Contact Cojo to schedule a platform inspection and scoping.
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