The Self-Enforcing Street Design Code

Also known as: The Vision Zero Design Mandate

The Core Mandate: Speed limits shall be determined by geometry, not signage. It is hereby prohibited to post a speed limit lower than the “Design Speed” of the roadway. If a street is designed for 40mph (wide lanes, clear zones), it cannot be signed for 20mph. To lower the limit, the city must physically alter the street geometry to make high speeds uncomfortable.

---

1. The Value Stack (Why This Matters)

🧪 The Science: “The Optical Narrowing Effect”

Drivers do not look at speedometers; they drive as fast as the road “feels.”

• The Psychology: Wide, open lanes signal “Highway” to the brain, causing involuntary acceleration.
• The Physics: Planting trees close to the curb or narrowing lanes creates “Visual Friction.” This triggers the Optical Narrowing Effect, causing drivers to instinctively slow down by 10-15mph to maintain comfort levels.

❤️ The Life: “The 20mph Survival Line”

Kinetic energy increases exponentially with speed. A small reduction in speed creates a massive increase in survival.

• 30 mph Impact: ~50% chance of pedestrian survival.
• 20 mph Impact: ~90% chance of pedestrian survival.
• The Rule: All residential and high-pedestrian zones must be designed for a 20 mph maximum impact speed.

💼 The Business: “The Cafe Zone”

• The Trade: Narrowing vehicle lanes releases 4-8 feet of public right-of-way.
• The Profit: This reclaimed space is converted into wider sidewalks and “Furniture Zones” (outdoor dining/retail displays).
• The Stat: Streets with high “Walkability Scores” and outdoor seating generate +30-50% higher revenue for local retail compared to car-centric stroads.

Real-World Examples:

• Barcelona, Spain: The Superblocks program redesigns entire neighborhoods with traffic-calmed interiors, reducing through-traffic speeds to 10 km/h (6 mph) through physical geometry. See C40 Cities Barcelona Superblocks Case Study.
• Netherlands: The Sustainable Safety program mandates self-explaining road design where geometry matches function—residential streets are physically designed for 30 km/h maximum speeds. See Dutch Road Safety Initiatives and PIARC Road Safety Guide.

---

2. Implementation Mechanisms

2.1 The “10-Foot” Lane Standard

• Prohibition: 12-foot travel lanes (standard highway width) are banned on urban streets.
• Mandate: Travel lanes shall be a maximum of 10 feet (3.0m).
• Effect: This forces driver attention and naturally caps speeds at ~35mph without police enforcement.

2.2 Vertical Deflection (The “Speed Table”)

• Requirement: Any crosswalk spanning more than 2 lanes must be raised to sidewalk level (a “Speed Table”).
• Function: This forces vehicles to slow to 15mph physically, prioritizes the pedestrian (who stays level), and acts as a mechanical enforcement of the speed limit.

2.3 The “Tree Shield” Requirement

• Mandate: Street trees must be planted between the sidewalk and the curb (not behind the sidewalk).
• Function: This creates a physical steel-and-timber barrier protecting pedestrians from cars, while simultaneously providing the “Visual Friction” needed to slow traffic.

---

3. The Integrity Engine Checks

🤖 The “Physicist” Agent Trigger

• Logic: The AI scans engineering road plans.
• The Test: IF signed_speed < 30mph AND lane_width > 10ft THEN flag_error("🚨 FATAL DESIGN FLAW: Geometry contradicts Signage.")
• Why: You cannot put a 20mph sign on a road designed for 45mph. That is an engineering hallucination.

---

4. Enforcement & Penalties

1. Design Certification: A construction permit shall be issued only after stamped plans certify that design speed, lane widths, and vertical deflection meet this code, and any active permit shall be suspended if the certification is missing. The transportation department shall log this approval as a mandatory pre-condition for every corridor project.
2. Field Verification: Inspectors shall conduct post-construction audits within 90 days of opening. Streets that fail the geometry test trigger immediate closure to through traffic, and the applicable building permit shall be revoked until the retrofit is verified.
3. Financial Consequences: Developers and contractors that open a non-compliant street shall pay fines up to $25,000 per segment and reimburse the city for temporary traffic-calming installations. Repeat violations trigger a two-year suspension from future city contracts and ineligibility for new right-of-way permits.

---

🤝 For the Business Community (BIA)

Bottom Line Impact:

• CapEx (Upfront Cost): Neutral to Low Savings. Less asphalt to pour/maintain means lower road costs. Trees cost less than concrete.
• Revenue Opportunity: High. Creating a “Patio Zone” essentially gives restaurants free square footage to expand their seating capacity.
• Liability: “Self-Enforcing” streets reduce catastrophic accidents, lowering municipal liability insurance premiums.

---

🗣️ The Drafting Room

This policy is a living document. Help us break it, fix it, and pass it.

🧪 Science Check

• Emergency Vehicles: Fire Departments often demand 12-foot lanes. Does the “10-Foot Standard” hinder fire trucks in your city? Can we use “Mountable Curbs” as a compromise?
• The “Tree” Risk: Do street trees block sightlines at intersections? How do we balance “Visual Friction” with “Intersection Visibility”?

💼 Business Reality

• Delivery Loading: If we narrow the street, where does the Amazon truck park? Do we need dedicated “Loading Zones” every 100 meters to prevent double-parking chaos?

🏠 Local Life

• The “Speed Bump” Hate: Residents often hate the noise of cars hitting speed bumps. Are “Speed Cushions” (which allow fire trucks to pass smoothly) a better option?

👉 Join the Official Discussion on GitHub ** layout: policy title: The Self-Enforcing Street Design Code id: self-enforcing-streets status: Draft tags: [transportation, safety, urban-design, vision-zero] discussion_id: vision-zero-feedback **

The Self-Enforcing Street Design Code

Also known as: The Vision Zero Design Mandate

The Core Mandate: Speed limits shall be determined by geometry, not signage. It is hereby prohibited to post a speed limit lower than the “Design Speed” of the roadway. If a street is designed for 40mph (wide lanes, clear zones), it cannot be signed for 20mph. To lower the limit, the city must physically alter the street geometry to make high speeds uncomfortable.

---

1. The Value Stack (Why This Matters)

🧪 The Science: “The Optical Narrowing Effect”

Drivers do not look at speedometers; they drive as fast as the road “feels.”

• The Psychology: Wide, open lanes signal “Highway” to the brain, causing involuntary acceleration.
• The Physics: Planting trees close to the curb or narrowing lanes creates “Visual Friction.” This triggers the Optical Narrowing Effect, causing drivers to instinctively slow down by 10-15mph to maintain comfort levels.

❤️ The Life: “The 20mph Survival Line”

Kinetic energy increases exponentially with speed. A small reduction in speed creates a massive increase in survival.

• 30 mph Impact: ~50% chance of pedestrian survival.
• 20 mph Impact: ~90% chance of pedestrian survival.
• The Rule: All residential and high-pedestrian zones must be designed for a 20 mph maximum impact speed.

💼 The Business: “The Cafe Zone”

• The Trade: Narrowing vehicle lanes releases 4-8 feet of public right-of-way.
• The Profit: This reclaimed space is converted into wider sidewalks and “Furniture Zones” (outdoor dining/retail displays).
• The Stat: Streets with high “Walkability Scores” and outdoor seating generate +30-50% higher revenue for local retail compared to car-centric stroads.

---

2. Implementation Mechanisms

2.1 The “10-Foot” Lane Standard

• Prohibition: 12-foot travel lanes (standard highway width) are banned on urban streets.
• Mandate: Travel lanes shall be a maximum of 10 feet (3.0m).
• Effect: This forces driver attention and naturally caps speeds at ~35mph without police enforcement.

2.2 Vertical Deflection (The “Speed Table”)

• Requirement: Any crosswalk spanning more than 2 lanes must be raised to sidewalk level (a “Speed Table”).
• Function: This forces vehicles to slow to 15mph physically, prioritizes the pedestrian (who stays level), and acts as a mechanical enforcement of the speed limit.

2.3 The “Tree Shield” Requirement

• Mandate: Street trees must be planted between the sidewalk and the curb (not behind the sidewalk).
• Function: This creates a physical steel-and-timber barrier protecting pedestrians from cars, while simultaneously providing the “Visual Friction” needed to slow traffic.

---

3. The Integrity Engine Checks

🤖 The “Physicist” Agent Trigger

• Logic: The AI scans engineering road plans.
• The Test: IF signed_speed < 30mph AND lane_width > 10ft THEN flag_error("🚨 FATAL DESIGN FLAW: Geometry contradicts Signage.")
• Why: You cannot put a 20mph sign on a road designed for 45mph. That is an engineering hallucination.

---

🤝 For the Business Community (BIA)

Bottom Line Impact:

• CapEx (Upfront Cost): Neutral to Low Savings. Less asphalt to pour/maintain means lower road costs. Trees cost less than concrete.
• Revenue Opportunity: High. Creating a “Patio Zone” essentially gives restaurants free square footage to expand their seating capacity.
• Liability: “Self-Enforcing” streets reduce catastrophic accidents, lowering municipal liability insurance premiums.

---

🗣️ The Drafting Room

This policy is a living document. Help us break it, fix it, and pass it.

🧪 Science Check

• Emergency Vehicles: Fire Departments often demand 12-foot lanes. Does the “10-Foot Standard” hinder fire trucks in your city? Can we use “Mountable Curbs” as a compromise?
• The “Tree” Risk: Do street trees block sightlines at intersections? How do we balance “Visual Friction” with “Intersection Visibility”?

💼 Business Reality

• Delivery Loading: If we narrow the street, where does the Amazon truck park? Do we need dedicated “Loading Zones” every 100 meters to prevent double-parking chaos?

🏠 Local Life

• The “Speed Bump” Hate: Residents often hate the noise of cars hitting speed bumps. Are “Speed Cushions” (which allow fire trucks to pass smoothly) a better option?

👉 Join the Official Discussion on GitHub