Intersection Capacity Calculator

Model intersection throughput with lane and signal factors. Review capacity, reserve, and v/c instantly online. Plan safer operations using responsive charts and export tools.

Enter Intersection Inputs

Formula Used

1) Adjusted demand flow
v = Hourly Volume / Peak Hour Factor
2) Saturation flow
s = Base Saturation Flow × Lanes × fw × fhv × fg × fp × fa × fu
3) Effective green and green ratio
g = Displayed Green − Lost Time
g/C = Effective Green / Cycle Length
4) Capacity and reserve
c = s × (g/C)
Reserve Capacity = c − v
5) v/c ratio and simplified delay
x = v / c
d = 0.5C(1 − g/C)2 / [1 − min(1,x)(g/C)]

This planner uses a practical signalized-intersection framework. It helps compare demand, timing, and adjustment factors quickly during design checks, concept studies, or operational reviews.

How to Use This Calculator

  1. Enter the observed hourly lane-group demand in vehicles per hour.
  2. Set the number of effective lanes serving that movement.
  3. Enter the base saturation flow, usually near local design guidance.
  4. Apply adjustment factors for width, heavy vehicles, grade, blockage, and area conditions.
  5. Enter displayed green, cycle length, and total lost time.
  6. Set peak hour factor and a planning target v/c ratio.
  7. Press Calculate Capacity to view metrics, graph, and report tools.
  8. Use the example table below to compare typical operating conditions.

Example Data Table

Scenario Hourly Volume Lanes Green Cycle Adj. Demand Capacity v/c Delay LOS
AM Peak 980 2 36 s 90 s 1,021 veh/h 1,258 veh/h 0.81 26.3 s/veh C
Midday 1,350 2 48 s 96 s 1,421 veh/h 1,523 veh/h 0.93 24.6 s/veh C
PM Peak 1,780 2 50 s 110 s 1,935 veh/h 1,213 veh/h 1.59 32.5 s/veh C

These examples are illustrative. Field calibration and local signal policies should guide final engineering decisions.

FAQs

1) What does intersection capacity mean?

It is the maximum traffic volume a lane group can serve during the analysis period under given signal timing, geometry, and traffic conditions.

2) Why is peak hour factor included?

Peak hour factor converts hourly demand into a more realistic peak flow rate. Lower values indicate sharper surges and usually reduce operational comfort.

3) What is saturation flow?

Saturation flow estimates how many vehicles can discharge per hour of effective green under prevailing field conditions for the studied movement.

4) What does a v/c ratio above 1.00 show?

A value above 1.00 suggests demand exceeds available capacity. That often indicates growing queues, unstable operation, and a likely need for timing or geometry changes.

5) Is the delay output exact?

No. It is a simplified planning estimate. Detailed design should use field counts, signal coordination effects, and full capacity analysis guidance.

6) Can I use this for unsignalized intersections?

Not directly. This setup is meant for signalized lane groups using green ratio and saturation concepts rather than gap-acceptance control.

7) Why do adjustment factors matter?

They account for conditions that change discharge rates, such as heavy vehicles, narrow lanes, grades, curb friction, and local operational effects.

8) What target v/c ratio should I choose?

Many planners screen operations around 0.85 to 0.95, but acceptable targets depend on policy, reliability needs, and growth expectations.

Input Guidance

  • Base saturation flow: Start with local standard values.
  • Lane width factor: Use less than 1.00 for constrained lanes.
  • Heavy vehicle factor: Lower values reduce discharge performance.
  • Parking blockage factor: Use lower values when curb friction is relevant.
  • Lost time: Include startup and clearance losses.
  • Target v/c: Use for planning volume thresholds.

Good Practice Notes

Use observed turning counts where possible.

Check each critical lane group separately.

Compare results against field queues and delay.

Recalculate after timing or lane changes.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.