Simple calculator for Rotary vs traffic signal decisions

Rotary vs Traffic Signal — Clean Decision Output (IRC referenced)

Enter site values below and click Calculate. The tool applies IRC‑referenced rules and outputs a clean scoring table with IRC clause references and final recommendation.

Are approach flows balanced? (approx. within ±25%) YesNo

Peak entering volume (veh/hr) — typical approach

Right-turn share (%)

Pedestrian crossing (p/h)

Reported accidents last 12 months (count)

85th percentile speed (km/h)

Available central island diameter (m) — set 0 if none

Criterion	IRC Reference	Condition met	Rotary pts	Signal pts

Total Rotary Score: 0

Total Signal Score: 0

Notes: The points and IRC references are for guidance and documentation. Always apply full IRC code and local engineering judgement for final decision and design.

Prepared per user request — clean output format with IRC clause references.

Detailed Solved Example & Engineering Manual

1. Indian Roads Congress (IRC) Evaluation Criteria

• Flow Balance (IRC:65-2017 Cl. 5.2.1): Balanced approach flows allow efficient continuous weaving without locking up any approach (+18 Rotary).
• Peak Entering Volume (IRC:65-2017 Cl. 5.3): Rotaries perform best between 500–1499 veh/hr (+12 Rotary). Above 1500 veh/hr, signal control handles higher capacities better (+8 Signal).
• Right-Turn Percentage (IRC:65-2017 Cl. 5.5): High right-turn demand (≥40%) heavily favors rotaries (+10 Rotary) as turning movements weave continuously without signal delays.
• Pedestrian Conflicts (IRC:93-1985 / IRC:SP:41): Heavy pedestrian crossings (≥150 p/h) demand traffic signals (+20 Signal) to provide dedicated pedestrian signal phases for safety.
• Accident History (IRC:93-1985 Warrant-4 / IRC:65-2017 Cl. 7.1): High accident intersections (≥5/yr) warrant signalization (+18 Signal) to reduce high-angle conflict points.
• Approach Speeds (IRC:65-2017 Cl. 5.7): High-speed approaches (≥60 km/h) make un-signalized merging dangerous (+10 Signal). Lower speeds (<50 km/h) suit rotaries (+2 Rotary).
• Available Diameter (IRC:65-2017 Cl. 6.2): A central island diameter ≥15 m provides sufficient weaving length (+8 Rotary). Space constraints heavily favor signals (+12 Signal).

2. Worked Solved Example (Default Input Values)

Input Conditions: Balanced Flows = Yes | Entering Volume = 900 veh/hr | Right Turns = 20% | Pedestrians = 60 p/h | Accidents = 1/yr | 85th Speed = 45 km/h | Island Diameter = 30 m

Step-by-Step Scoring:

1. Approach Balance: Balanced → Rotary +18
2. Entering Volume: 900 veh/hr (Range 500–1499) → Rotary +12
3. Right Turns: 20% (Moderate range 15–39%) → Rotary 0, Signal 0
4. Pedestrians: 60 p/h (Moderate range 50–149) → Signal +6
5. Accidents: 1 accident/yr (<2) → Rotary +2
6. 85th Speed: 45 km/h (<50 km/h) → Rotary +2
7. Island Diameter: 30 m (≥15 m) → Rotary +8

Final Verdict Calculation:

• Total Rotary Score: 18 + 12 + 0 + 0 + 2 + 2 + 8 = 42 Points
• Total Signal Score: 0 + 0 + 0 + 6 + 0 + 0 + 0 = 6 Points
• Score Difference: |42 - 6| = 36 points (> 8 points threshold)
• Conclusion: PREFER ROTARY (ROUNDABOUT)

Prepared for traffic engineering analysis per IRC:65-2017 and IRC:93-1985 standards.