Enter Traffic Inputs
Example Data Table
| Scenario | Observed Count | Interval | Avg Speed | Lanes | Hourly Flow | Lane Density | LOS |
|---|---|---|---|---|---|---|---|
| Morning peak | 420 | 15 min | 48 km/h | 3 | 1,680 veh/h | 6.76 veh/km/ln | A |
| Midday | 300 | 15 min | 56 km/h | 3 | 1,200 veh/h | 4.14 veh/km/ln | A |
| Evening peak | 520 | 15 min | 34 km/h | 3 | 2,080 veh/h | 11.82 veh/km/ln | C |
Formula Used
Hourly flow rate: q = observed count × 60 ÷ count interval.
Peak hour factor: PHF = hourly volume ÷ (4 × peak 15-minute volume).
Space mean speed: u = segment length ÷ travel time.
Density: k = flow ÷ speed. Lane density uses directional flow per lane.
Headway: h = 3600 ÷ flow per lane.
Spacing: s = 1000 ÷ lane density.
Heavy vehicle adjustment: equivalent demand = directional volume × [1 + heavy share × (PCE - 1)].
Signal capacity: c = adjusted saturation flow per lane × lanes × green ratio.
Segment capacity: base capacity = 2200 × lanes × width factor × adjustment factor.
Volume to capacity ratio: v/c = equivalent demand ÷ selected effective capacity.
Greenshields values: critical density = jam density ÷ 2, critical speed = free flow speed ÷ 2, and maximum flow = free flow speed × jam density ÷ 4.
How to Use This Calculator
Enter the observed vehicle count and the exact count interval first. Add the peak 15-minute count when you want a peak hour factor.
Provide either average speed or a segment length with travel time. The tool uses these values to estimate operating speed and density.
Add lane count, lane width, heavy vehicle share, and passenger car equivalent. These inputs improve capacity and demand estimates.
Use signal timing and base saturation flow for junction analysis. Leave signal values at zero only when you want a basic segment review.
Enter AADT, K-factor, and D-factor when you need design hour demand. Then compare observed demand with design demand.
Press the submit button. The result section appears above the form, directly below the header. Export the final table as CSV or PDF when needed.
Traffic Flow Analysis for Better Roadway Decisions
Why this analysis matters
Traffic flow analysis helps engineers understand how roads perform under real demand. It links speed, density, capacity, and delay. These values explain whether a corridor runs smoothly or moves toward breakdown. A strong review supports safer design, signal timing, lane planning, and congestion management.
Core traffic variables
Flow shows how many vehicles pass a point during a period. Speed shows how fast vehicles move. Density shows how closely they travel together. These three variables shape the fundamental traffic relationship. When density rises too far, speed falls. When speed falls sharply, stable flow can disappear.
Why lane and vehicle mix matter
Lane count changes service quality quickly. More lanes can spread demand and reduce headway pressure. Lane width also matters. Narrow lanes usually lower operating efficiency. Heavy vehicles influence performance too. Trucks and buses occupy more road space and need more time to accelerate. That effect raises equivalent demand.
Using design hour demand
Observed counts describe current conditions. Design values describe future checks. AADT, K-factor, and D-factor help estimate peak directional demand. This is useful for corridor planning, intersection upgrades, and widening studies. It allows engineers to compare today’s flow with future operating needs.
Signal and capacity review
At signalized locations, green time and cycle length shape capacity. A shorter green split reduces discharge opportunity. That can increase volume to capacity ratio and control delay. Delay is important because users feel it directly. It also supports level of service review at intersections.
Applying the results
This calculator combines count data, speed data, heavy vehicle share, signal settings, and design factors in one place. Use it for quick screening, concept design, classroom work, and engineering checks. The best practice is to compare multiple scenarios, test peak conditions, and document assumptions clearly before final design decisions.
FAQs
1. What does traffic flow analysis measure?
It measures how vehicles move on a road or through an intersection. Common outputs include flow rate, speed, density, capacity, delay, headway, spacing, and level of service.
2. Why is peak hour factor important?
Peak hour factor shows how evenly traffic is spread within the peak hour. A lower value means traffic is concentrated in a shorter burst, which usually increases operational stress.
3. What is the difference between flow and capacity?
Flow is the actual or observed traffic demand. Capacity is the maximum rate that can reasonably pass under prevailing roadway, control, and traffic conditions.
4. Why do heavy vehicles affect the result?
Heavy vehicles take more road space and usually accelerate slower. They reduce efficiency, so engineers often convert them into passenger car equivalents for better comparison.
5. When should I use AADT, K-factor, and D-factor?
Use them when you want a design hour estimate from daily traffic. They are helpful for future planning, preliminary geometric design, and corridor expansion checks.
6. What does v/c ratio tell me?
The volume to capacity ratio shows how close demand is to the available capacity. Higher values indicate a busier facility and a greater risk of unstable flow.
7. Can this calculator be used for signalized intersections?
Yes. Enter green time, cycle time, and saturation flow. The calculator will estimate signal capacity and an approximate control delay for the analyzed movement.
8. Is the result suitable for final design alone?
No. It is useful for screening and early checks. Final design should also use field observations, local standards, detailed turning data, and full engineering judgment.