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A Complete Guide to Detectable Warnings or Truncated Domes: When and Why They're Required

  • Writer: Corey Taylor
    Corey Taylor
  • Aug 28
  • 6 min read
Detectable warnings or truncated domes at a curb cut ramp with an arrow pointing at it. There is also a slope level sitting at the access aisle


Ever noticed those yellow bumpy surfaces at crosswalks and wondered what they're for? As a property owner or tenant, understanding detectable warnings isn't just about curiosity—it's about avoiding lawsuits that can cost thousands of dollars.



What Are Detectable Warnings and Why Should You Care?


Picture this: You're walking to your car after grocery shopping, scrolling through your phone, when suddenly you feel those distinctive bumps under your feet. That tactile surface just saved you from wandering into traffic without looking up.


Detectable warnings are those standardized yellow surfaces with raised truncated domes that serve as "tactile stop signs" for people with visual impairments. But here's what many property owners don't realize—they protect everyone, not just the visually impaired.



The Real Problem They Solve


Before curb ramps became common, people with visual impairments could easily detect the edge of a sidewalk by feeling the raised curb with their cane. But when we added ramps to help wheelchair users, we accidentally created a dangerous situation for blind pedestrians—they could no longer tell where the safe sidewalk ended and dangerous vehicle traffic began.


The result? Blind travelers fail to detect streets before stepping into traffic at curb ramps without detectable warnings. That's why these surfaces became legally required.



Understanding Your Legal Requirements: Federal vs. California


Here's where it gets tricky—the rules are different depending on whether you're following federal ADA Standards or California's more stringent requirements.



Federal ADA Standards (Minimum Requirements)


Under the 2010 ADA Standards, detectable warnings are only required at:


  • Transit platform boarding edges (trains, buses, rail)

  • Curb ramps at transportation facilities only (airports, transit stations)


Citation: 2010 ADA Standards, Section 705.2

That's it. The federal requirements are surprisingly limited.



California Building Code Chapter 11B (Much More Extensive)


California requires detectable warnings at seven different types of locations:


  1. All curb ramps (perpendicular and parallel)

  2. Platform edges (transit boarding areas)

  3. Islands and cut-through medians (pedestrian refuges)

  4. Blended transitions (flush connections to parking lots)

  5. Bus stops (transit boarding areas)

  6. Track crossings (at-grade rail crossings)

  7. Reflecting pool edges (if not protected by barriers)


Citation: CBC 11B-247.1.2 and CBC 11B-705.1.2


Bottom Line for California Properties: You need to follow CBC Chapter 11B requirements, which are much more comprehensive than federal standards.



Real-World Examples: Where You'll See Them

Shopping Center Parking Lot Scenario


Let's walk through a typical shopping center to see where detectable warnings are required:


✅ Required Locations:

  • Curb ramps from sidewalks to parking areas

  • Pedestrian refuge islands in the middle of drive lanes

  • Blended transitions where sidewalks meet parking areas without curbs

  • Bus stop areas (if applicable)


Citation: CBC 11B-705.1.2.2 for curb ramps, CBC 11B-705.1.2.3 for islands



Transit Station Example


At a train or bus station, you'll find detectable warnings:

  • Along platform edges - 24 inches wide, full length of platform

  • At track crossings where pedestrians cross rails to reach platforms


Citation: CBC 11B-705.1.2.1 for platforms, CBC 11B-705.1.2.7 for track crossings



Office Building Campus


Around office buildings, detectable warnings appear at:

  • All curb ramps connecting sidewalks to parking areas

  • Pedestrian walkways that cross vehicular drives without curbs


Citation: CBC 11B-705.1.2.2 and CBC 11B-705.1.2.5



Technical Specifications You Need to Know

California Requirements (More Stringent)


Dome Specifications:

  • Base diameter: 0.9" to 0.92" (much tighter tolerance than federal)

  • Top diameter: 0.45" to 0.47"

  • Height: 0.2 inches exactly

  • Spacing: 2.3" to 2.4" center-to-center between domes


Citation: CBC 11B-705.1.1.1 and CBC 11B-705.1.1.2



Size and Placement Requirements


  • Curb ramps: 36 inches deep, full width of ramp excluding flared sides

  • Platform edges: 24 inches wide, full length of platform

  • Visual contrast: Minimum 70% contrast with adjacent surfaces

  • Color: Safety yellow (Federal Color No. 33538) for most applications


Citation: CBC 11B-705.1.2 for placement, CBC 11B-705.1.1.3 for color



Where Detectable Warnings Are PROHIBITED (Critical to Avoid Mistakes)


This is where many consultants and contractors get it wrong.California code specifically PROHIBITS detectable warnings in certain areas:


❌ NEVER Install Detectable Warnings In:

  • Parking spaces (including accessible spaces)

  • Access aisles (next to accessible parking)

  • Passenger drop-off zones and their access aisles

  • Door landings (entrances to buildings)

  • Ramp landings (on accessibility ramps)

  • Clear floor spaces (areas required to be level)

  • Wheelchair turning spaces

  • Stair treads


Why This Matters: Installing detectable warnings in prohibited areas creates serious safety hazards and can result in expensive lawsuits.



Common Costly Mistakes (That Even Professionals Make)

Mistake #1: The "More is Better" Fallacy


Real Example: A major retailer's parking lot has detectable warnings installed at seven different locations between the sidewalk and entrance, when only two are required.


The Problem: This confuses visually impaired users who rely on these surfaces as navigation cues. When they encounter multiple warning surfaces in what should be a safe pedestrian area, they can't tell where the actual hazards are.


The Fix: Only install detectable warnings where specifically required by code.



Mistake #2: Missing the Curb Ramp Entirely


Real Example: Contractors install detectable warnings on a sidewalk but forget to build the actual curb ramp, leaving a 6-inch drop.


The Problem: Blind pedestrians feel the warning surface and expect a ramp, then fall when they step down unexpectedly.


The Fix: Always ensure the physical infrastructure matches the warning system.



Mistake #3: Wrong Color Requirements


Real Example: Using generic colored detectable warnings instead of required safety yellow.


The Problem: California requires safety yellow (Federal Color #33538) for most applications. Using other colors, even if they contrast, may not meet code.


The Fix: Verify color requirements for your specific application.


Citation: CBC 11B-705.1.1.3



Mistake #4: Installing in Prohibited Areas


Real Example: Placing detectable warnings inside accessible parking spaces.


The Problem: This creates obstacles for wheelchair users and violates ADA requirements for level parking surfaces.


The Fix: Learn where detectable warnings are specifically prohibited.



Mistake #5: Incorrect Sizing and Spacing


Real Example: Using federal specifications (0.9"-1.4" dome diameter) instead of California's tighter requirements (0.9"-0.92").


The Problem: California inspectors will cite non-compliant installations, requiring expensive replacement.


The Fix: Always use California CBC specifications for California projects.


Citation: CBC 11B-705.1.1.1



Step-by-Step Property Assessment Guide


Step 1: Identify Your Required Locations


Walk your property with this checklist:


✅ Curb Ramps Checklist:

  • All perpendicular curb ramps (straight down from sidewalk)

  • All parallel curb ramps (along the street)

  • Ramps from sidewalks to parking areas

  • Ramps at building entrances


✅ Transit Areas Checklist:

  • Bus stops (if on your property)

  • Platform edges (if applicable)

  • Track crossings (if applicable)


✅ Vehicular Transition Checklist:

  • Blended transitions (flush sidewalk to parking)

  • Pedestrian islands in parking lots

  • Cut-through medians at crosswalks



Step 2: Verify What You DON'T Need


✅ Prohibited Areas Checklist:

  • No detectable warnings IN parking spaces

  • No detectable warnings IN access aisles

  • No detectable warnings on ramp landings

  • No detectable warnings at door entrances

  • No detectable warnings on stair treads



Step 3: Measure and Specify


For each required location:

  • Width: Full width of ramp/platform

  • Depth: 36" for curb ramps, 24" for platforms

  • Color: Safety yellow (Federal Color #33538)

  • Product: DSA-AC approved for California


Citation: CBC 11B-705.3 for product approval



Step 4: Professional Installation


  • Use only California-approved products

  • Ensure proper dome spacing (2.3"-2.4" center-to-center)

  • Verify 70% color contrast

  • Get proper permits and inspections



Pro Tips from the Field

What Accessibility Experts Recommend:


  1. Always err on the side of California requirements - they're more protective than federal standards

  2. Consult a Certified Access Specialist (CASp) before major installations

  3. Document your compliance with photos and specifications

  4. Regular maintenance - damaged or worn detectable warnings lose their effectiveness

  5. Think like a blind pedestrian - would these warnings make sense to someone who can't see?



Red Flags to Watch For:


  • Contractors who don't know California vs. federal differences

  • "One-size-fits-all" approaches to detectable warnings

  • Installations that seem excessive or confusing

  • Missing technical specifications or product approvals



Your Next Steps

For New Construction:


  1. Include detectable warning requirements in your architectural plans

  2. Specify California CBC Chapter 11B compliance

  3. Require DSA-AC approved products

  4. Plan for proper placement during design phase



For Existing Properties:


  1. Conduct a thorough property assessment using this guide

  2. Prioritize high-traffic and high-liability areas

  3. Budget for phased compliance if needed

  4. Consider hiring a CASp for complex situations



For Property Management:


  1. Include detectable warnings in your regular maintenance inspections

  2. Train staff to identify damage or wear

  3. Keep documentation of compliance efforts

  4. Stay updated on code changes



The Bottom Line


Detectable warnings aren't just about legal compliance—they're about creating safe, accessible environments for everyone who visits your property. When installed correctly, they prevent accidents and lawsuits while demonstrating your commitment to accessibility.


Key Takeaways:

  • California requirements are much more extensive than federal ADA standards

  • More isn't always better—incorrect placement can be dangerous

  • Professional consultation can save thousands in retrofit costs

  • Proper installation protects both users and property owners


Remember: The goal isn't just to avoid lawsuits—it's to create spaces that work safely for everyone. When you get detectable warnings right, you're not just checking a compliance box; you're potentially saving someone from serious injury.



DISCLAIMER: The information provided in this post is for informational purposes only and does not constitute legal advice. Please consult a qualified attorney or consultant for advice tailored to your situation.

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