Street Design

Street Design Skill

This skill provides comprehensive street design guidance based on NACTO Urban Street Design Guide, Global Designing Cities Initiative (GDCI), AASHTO Green Book, and international best practices. It covers the full workflow from street hierarchy classification through cross-section dimensioning, intersection design, streetscape specification, and traffic calming.

1. Street Hierarchy Classification

Use the following decision tree to classify any street. Start with the Average Daily Traffic (ADT) count, then apply contextual modifiers.

Primary Classification by ADT and Function

Arterial (>15,000 ADT)

• Right-of-Way (ROW): 30-40m
• Lanes: 2-3 per direction (3.0-3.3m each)
• Design speed: 40-50 km/h (urban), 50-60 km/h (suburban)
• Transit: dedicated bus/BRT lanes strongly recommended
• Cycling: protected bike lanes required (physically separated)
• Pedestrian: wide sidewalks 3.6-6.0m, pedestrian refuge islands at crossings
• Median: 3.0-6.0m landscaped or transit median
• Signal spacing: 200-400m typical
• Role: city-wide movement, connects districts, carries transit trunk routes

Collector (3,000-15,000 ADT)

• ROW: 22-30m
• Lanes: 1-2 per direction (3.0-3.3m each)
• Design speed: 30-40 km/h
• Transit: on-street bus stops with boarding islands
• Cycling: protected bike lanes or buffered bike lanes
• Pedestrian: generous sidewalks 2.4-3.6m
• Median: optional, 1.8-3.0m where present
• Role: connects neighborhoods to arterials, local commercial corridors

Local Street (<3,000 ADT)

• ROW: 15-22m
• Lanes: 1 per direction (2.7-3.0m each)
• Design speed: 30 km/h
• Transit: typically no fixed-route transit
• Cycling: shared lane markings (sharrows) or separated bike lanes depending on context
• Pedestrian: standard sidewalks 1.8-2.4m
• Parking: parallel one or both sides
• Role: neighborhood access, residential frontage, low-speed environment

Shared Street / Woonerf (<1,000 ADT)

• ROW: 8-15m
• Lanes: single surface, no lane markings
• Design speed: 10-20 km/h
• Cycling: shared surface, cyclists and pedestrians together
• Pedestrian: priority over vehicles, no curb separation
• Surface: textured paving, bollards, planters as speed controls
• Role: residential living streets, market streets, festival routes

Pedestrian Priority Street (variable ADT, typically <500)

• ROW: variable (4-20m)
• Vehicles: no through-traffic, emergency and service access only
• Design speed: 5-10 km/h (service vehicles only)
• Surface: high-quality paving, level, no curbs
• Role: retail promenades, civic spaces, historic cores

Contextual Modifiers

Apply these modifiers after primary classification to adjust cross-section priorities:

2. Cross-Section Design Methodology

Design cross-sections layer by layer, working from the building face toward the street centerline. Each layer has a defined function and dimensional range.

Layer Sequence (Building Face to Centerline)

BUILDING FACE
  |
  |--> [A] Building Setback (context-dependent)
  |--> [B] Frontage Zone (0.3 - 0.9m)
  |--> [C] Pedestrian Clear Zone (1.8 - 3.6m)
  |--> [D] Furnishing / Planting Zone (0.6 - 1.8m)
  |--> [E] Cycle Track + Buffer (optional: 1.5-2.5m track + 0.3-0.6m buffer)
  |--> [F] Parking Lane (optional: 2.1 - 2.4m parallel, 4.5-5.5m angled)
  |--> [G] Travel Lane(s) (3.0 - 3.3m each)
  |--> [H] Median (optional: 1.2 - 6.0m)
  |
  CENTERLINE (mirror layers G through A for opposite side)

Layer Definitions

[A] Building Setback Not part of the public ROW but affects street enclosure. Zero setback for urban retail frontage, 1.5-3.0m for residential, 3.0-6.0m+ for suburban or institutional.

[B] Frontage Zone (0.3 - 0.9m) The strip immediately adjacent to the building face. Accommodates door swings, window displays, awning drip lines, basement vault covers. In commercial areas, may include outdoor dining or merchandise display (with permit, requiring wider dimension of 1.2-2.4m).

[C] Pedestrian Clear Zone (1.8 - 3.6m) The unobstructed walking path. This is the most critical pedestrian dimension. No street furniture, signs, trees, or other obstructions. Minimum 1.8m allows two wheelchairs to pass. Recommended 2.4m for residential, 3.0m for commercial, 3.6m+ for high-volume pedestrian areas. Must comply with ADA/accessibility requirements: maximum cross-slope 2%, smooth and continuous surface.

[D] Furnishing / Planting Zone (0.6 - 1.8m) Contains street trees, light poles, sign posts, parking meters, benches, trash receptacles, bicycle racks, utility access covers. Serves as a buffer between pedestrians and the roadway. Tree wells minimum 1.5m x 1.5m, continuous tree trench preferred. Bioswales and rain gardens can be integrated here.

[E] Cycle Track + Buffer (optional) One-way protected bike lane: 1.5m minimum, 2.0m recommended, 2.5m for high-volume. Two-way cycle track: 2.4m minimum, 3.0m recommended, 3.6m+ for high-volume. Buffer between cycle track and travel/parking lane: 0.3m minimum (painted), 0.6m recommended (with vertical elements such as bollards, planters, or curb).

[F] Parking Lane (optional) Parallel parking: 2.1m minimum, 2.4m recommended (allows door opening without encroaching on bike lane). Angled parking (45-degree): 4.5-5.5m. Angled parking (60-degree): 5.2-5.8m. Perpendicular parking (90-degree): 5.5-6.0m. Consider flex zones: parking by day, loading in morning, outdoor dining in evening.

[G] Travel Lane(s) General travel lane: 3.0m minimum urban, 3.3m standard (NACTO). Bus/transit lane: 3.3-3.6m. Right-turn lane: 2.7-3.0m. Left-turn lane: 3.0-3.3m. Never exceed 3.6m for any urban lane (wider lanes induce higher speeds). Reduce to 2.7m for yield streets and very low-speed environments.

[H] Median (optional) Pedestrian refuge: 1.8m minimum (2.4m with accessibility), allows stroller or wheelchair to wait. Landscaped median: 2.4-6.0m, with trees, ground cover, stormwater management. Transit median: 3.6-5.0m for center-running BRT/LRT with platforms. Left-turn pocket in median: 3.0-3.3m wide, 30-45m long.

Worked Example: Urban Collector Street (26m ROW)

   2.4m   |  3.0m  | 1.2m |2.0m|0.6| 2.4m | 3.0m | 3.0m | 3.0m | 2.4m |0.6|2.0m| 1.2m |  3.0m  | 2.4m
 Frontage  | Ped CZ | Furn |Bike|Buf| Park | Lane | Lane | Lane | Park |Buf|Bike| Furn | Ped CZ | Frontage
           |        | Zone |    |   |      |  EB  |  EB  |  WB  |      |   |    | Zone |        |
   BLDG ---+--------+------+----+---+------+------+------+------+------+---+----+------+--------+--- BLDG

Wait -- the above totals to more than 26m. Let me provide a corrected, realistic example:

Worked Example: Urban Collector (26m ROW, Commercial Context)

 0.6 | 3.0  | 1.2  | 2.0+0.6 | 2.4  | 3.0  | 3.0  | 2.4  | 0.6+2.0 | 1.2  | 3.0  | 0.6
Front|PedCZ | Furn | Bike+Buf | Park | Lane | Lane | Park | Buf+Bike | Furn | PedCZ|Front
     |      | Zone |          |      |  EB  |  WB  |      |          | Zone |      |
BLDG-+------+------+----------+------+------+------+------+----------+------+------+-BLDG
= 0.6+3.0+1.2+2.6+2.4+3.0+3.0+2.4+2.6+1.2+3.0+0.6 = 25.6m (~26m)

Worked Example: Residential Local Street (18m ROW)

 0.3 | 1.8  | 1.2  | 2.1  | 3.0  | 3.0  | 2.1  | 1.2  | 1.8  | 0.3
Front|PedCZ | Furn | Park | Lane | Lane | Park | Furn | PedCZ|Front
     |      | Zone |      |  NB  |  SB  |      | Zone |      |
BLDG-+------+------+------+------+------+------+------+------+-BLDG
= 0.3+1.8+1.2+2.1+3.0+3.0+2.1+1.2+1.8+0.3 = 17.8m (~18m)

Worked Example: Arterial Boulevard (36m ROW)

 0.6 | 3.6  | 1.5  | 2.0+0.6 | 3.3  | 3.3  | 3.3  | 4.8  | 3.3  | 3.3  | 0.6+2.0 | 1.5  | 3.6  | 0.6
Front|PedCZ | Furn | Bike+Buf | Lane | Lane | Lane | Med  | Lane | Lane | Buf+Bike | Furn | PedCZ|Front
     |      | Zone |          |  EB  |  EB  |  EB  |      |  WB  |  WB  |          | Zone |      |
BLDG-+------+------+----------+------+------+------+------+------+------+----------+------+------+-BLDG
= 0.6+3.6+1.5+2.6+3.3+3.3+3.3+4.8+3.3+3.3+2.6+1.5+3.6+0.6 = 37.9m (~38m, adjust median to 2.9m for 36m)

Worked Example: Shared Street / Woonerf (12m ROW)

 1.5   |          9.0 single shared surface           | 1.5
Planter|  pedestrians + cyclists + vehicles at 15km/h |Planter
 zone  |  textured paving, flush, no curbs, bollards  | zone
BLDG---+----------------------------------------------+---BLDG
= 1.5+9.0+1.5 = 12.0m

3. Complete Street Elements Table

Pedestrian Zone Elements

Cycling Infrastructure

Travel Lanes

Parking

Medians

Street Furniture and Fixtures

4. Intersection Design

Compact Intersection Principles

Design intersections to be as compact as possible. Smaller intersections reduce pedestrian crossing distances, slow turning vehicles, improve sight lines, and reduce conflict points. Key principles:

• Minimize curb radii (tightest feasible for design vehicle)
• Eliminate unnecessary turn lanes
• Use curb extensions (bulb-outs) to shorten crossings
• Align crosswalks with pedestrian desire lines
• Provide pedestrian refuge islands for crossings >3 lanes
• Set back stop bars 1.2-2.4m from crosswalk (4.0m at signalized with bike box)

Curb Radius Standards

Note: Effective turning radius is often larger than the physical curb radius due to parking lane and bike lane setbacks. A 3.0m physical curb radius with a 2.4m parking lane yields an effective radius of approximately 7.5m, sufficient for buses and delivery trucks.

Pedestrian Crossing Types

Crossing Width Standards

Signal Timing for Pedestrians

• Minimum pedestrian walk phase: 7 seconds
• Pedestrian walking speed for clearance calculation: 1.2 m/s (standard), 1.0 m/s (elderly/school zones), 0.9 m/s (accessible design)
• Leading Pedestrian Interval (LPI): 3-7 seconds head start before parallel vehicle green
• Exclusive pedestrian phase (scramble): 15-25 seconds depending on crossing distances
• Pedestrian recall: recommended at all urban intersections (automatic pedestrian phase every cycle)
• Maximum wait time: 60-90 seconds (longer waits lead to non-compliance)

Roundabout Design

Roundabout pedestrian crossings: set back one car length (6.0m) from yield line, marked crosswalk, splitter island refuge minimum 1.8m wide.

5. Streetscape and Materials

Surface Materials by Zone

Street Tree Selection Criteria

Select species based on all of the following:

• Canopy spread: minimum 6m mature spread for shade, 8-12m for boulevards
• Root behavior: non-invasive root systems, deep-rooting species preferred, avoid surface root species near pavement
• Climate suitability: USDA hardiness zone compatible, drought tolerance for urban heat island, salt tolerance for winter-maintained streets
• Clearance: minimum 2.4m trunk clearance (pedestrian), 4.2m over bike lanes, 4.5m over roadways
• Soil volume: 15-20 cubic meters per tree minimum for healthy growth (use structural soil, silva cells, or continuous trenches)
• Maintenance: deciduous preferred for seasonal solar access, avoid messy fruit species over sidewalks, disease-resistant cultivars
• Spacing: 6.0-9.0m on center for continuous canopy, stagger with light poles

Lighting Standards

Green Infrastructure Integration

• Tree trenches: Continuous below-grade soil cells connecting multiple tree pits, shared soil volume, structural support for pavement above
• Bioswales: Located in furnishing zone or median, 0.6-1.8m wide, 150-300mm deep, planted with native grasses and sedges, accept road runoff through curb cuts
• Permeable paving: Use in parking lanes and furnishing zones, reduces runoff by 70-90%, requires regular vacuum sweeping
• Rain gardens: At curb extensions and median ends, capture and filter first flush of stormwater, sized for local rainfall intensity
• Stormwater planters: Contained planting areas with underdrains, suitable where infiltration is not feasible (high water table, contaminated soil)

6. Traffic Calming Toolkit

Measures by Target Speed Reduction

50 to 40 km/h (Arterial/Collector Transition)

• Road diet: convert 4 lanes to 3 (2 travel + center turn lane), reclaim space for bike lanes and wider sidewalks
• Curb extensions at intersections: narrow roadway from 12m to 9m at crossing points
• Median islands: 1.8m minimum width, planted, with pedestrian refuge
• Signal coordination at 40 km/h progression speed
• Roadway surface change at gateway (asphalt to textured)

40 to 30 km/h (Collector/Local Transition)

• Chicanes: alternating curb extensions that deflect the travel path laterally, 3.0-3.6m deflection
• Raised crossings: full-width speed tables at pedestrian crossings, 75-100mm height, 6.0m long platform
• Speed tables: flat-topped speed bumps, 6.0-7.5m long, 75-100mm height
• Gateway treatments: visual and physical narrowing at neighborhood entries
• Neckdowns: narrow roadway to one lane at pinch points, with priority signs

30 to 20 km/h (Local/Shared Street Transition)

• Pinch points: narrow roadway to 3.0-3.6m, one vehicle at a time, yield condition
• Raised intersections: entire intersection at sidewalk level, vehicles mount gentle ramp
• Horizontal deflection: S-curves using alternating parking or planting islands
• Surface material changes: transition from asphalt to unit pavers, textured concrete
• Vertical elements: trees, bollards, planters placed to reduce apparent width

20 to 10 km/h (Shared Street / Woonerf)

• Shared surface: remove curbs entirely, single-level surface
• Textured paving: cobblestone, unit pavers, or stamped concrete to create visual and physical friction
• Removable bollards: allow event closure and emergency access while defining edges
• Planting and furniture: place obstacles (planters, benches, play elements) in the vehicle path
• Tight geometry: no straight runs longer than 30-50m

7. Output Format

When producing a street design, deliver the following specification package:

Cross-Section Specification Template

STREET NAME: [Name]
CLASSIFICATION: [Arterial / Collector / Local / Shared / Pedestrian]
CONTEXT: [Commercial / Residential / Mixed-Use / Industrial / Other]
DESIGN SPEED: [km/h]
ADT: [vehicles/day]
ROW WIDTH: [m]

CROSS-SECTION (one side, building face to centerline):
+-----------+--------+-----------+
| Element   | Width  | Notes     |
+-----------+--------+-----------+
| Frontage  | X.Xm   |           |
| Ped CZ    | X.Xm   |           |
| Furnishing| X.Xm   |           |
| Bike Lane | X.Xm   | + X.Xm buffer |
| Parking   | X.Xm   |           |
| Travel Ln | X.Xm   | x N lanes |
| Median    | X.Xm   |           |
+-----------+--------+-----------+
TOTAL (half): XX.Xm
TOTAL (full): XX.Xm

ASCII CROSS-SECTION:
|BLD|Front|  Ped CZ  |Furn| Bike |Buf|Park| Lane | Lane |Med| Lane | Lane |Park|Buf| Bike |Furn|  Ped CZ  |Front|BLD|
|   | 0.6 |   3.0    |1.2 | 2.0  |0.6|2.4 | 3.0  | 3.0  |3.0| 3.0  | 3.0  |2.4 |0.6| 2.0  |1.2 |   3.0    | 0.6 |   |

INTERSECTION TREATMENT:
- Curb radius: X.Xm
- Crosswalk width: X.Xm
- Crossing type: [marked / raised / signalized]
- Pedestrian refuge: [yes/no, width]

STREETSCAPE:
- Trees: [species], [spacing]m o.c., [soil volume]m3 per tree
- Lighting: [pedestrian/roadway], [height]m poles, [spacing]m, [lux] target
- Surface: [material by zone]
- Furniture: [benches, racks, receptacles]
- Green infrastructure: [bioswales, permeable paving, rain gardens]

TRAFFIC CALMING:
- [List applicable measures]
- Target speed: [km/h]

8. Reference Links

Primary Standards and Guidelines

• NACTO Urban Street Design Guide: https://nacto.org/publication/urban-street-design-guide/
• NACTO Transit Street Design Guide: https://nacto.org/publication/transit-street-design-guide/
• NACTO Don't Give Up at the Intersection: https://nacto.org/publication/dont-give-up-at-the-intersection/
• NACTO Urban Bikeway Design Guide: https://nacto.org/publication/urban-bikeway-design-guide/
• Global Designing Cities Initiative (GDCI) Global Street Design Guide: https://globaldesigningcities.org/publication/global-street-design-guide/
• AASHTO A Policy on Geometric Design of Highways and Streets (Green Book): https://store.transportation.org/
• FHWA Manual on Uniform Traffic Control Devices (MUTCD): https://mutcd.fhwa.dot.gov/
• ADA Standards for Accessible Design: https://www.ada.gov/law-and-regs/design-standards/

Supplementary Resources

• FHWA Separated Bike Lane Planning and Design Guide: https://www.fhwa.dot.gov/environment/bicycle_pedestrian/publications/separated_bikelane_pdg/
• ITE Designing Walkable Urban Thoroughfares: https://www.ite.org/
• CROW Design Manual for Bicycle Traffic (Netherlands): https://crowplatform.com/
• Transport for London Streetscape Guidance: https://tfl.gov.uk/corporate/publications-and-reports/streets-toolkit
• Urban Street Stormwater Guide (NACTO): https://nacto.org/publication/urban-street-stormwater-guide/
• WHO Global Status Report on Road Safety: https://www.who.int/publications/i/item/9789241565684
• ITDP Transit-Oriented Development Standard: https://www.itdp.org/
• C40 Cities Green and Healthy Streets: https://www.c40.org/