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.