Dwelling Units (Residential)
1,000 Sq. Ft. Gross Floor Area (Commercial/Office)
Employees
Hotel Rooms
Parking Spaces
Students (School)
Fueling Positions (Gas Station)
Calculation Summary
Calculated Trip Generation Rate:
Interpretation:
Understanding Trip Generation Rates
Trip generation is the first step in the traditional four-step transportation forecasting process. It involves predicting the number of trips that will begin or end in a specific traffic analysis zone or at a particular land use site. This is critical for urban planners, civil engineers, and developers when performing Traffic Impact Studies (TIS).
The Mathematical Formula
The calculation is based on a linear relationship between the land use intensity and the movement of vehicles or people. The formula used in our calculator is:
T = R × X
Where:
T: Total trips generated.
R: Trip generation rate (Trips per unit of independent variable).
X: The quantity of the independent variable (e.g., thousands of square feet, number of units).
Common Independent Variables (IV)
Different land uses require different metrics to accurately predict traffic flow:
Land Use Type
Standard Independent Variable
Single-Family Housing
Number of Dwelling Units
Shopping Center
1,000 Sq. Ft. Leasable Area (GLA)
General Office Building
1,000 Sq. Ft. Gross Floor Area (GFA)
University/School
Number of Students or Employees
Example Calculation
Imagine you are analyzing a proposed 50-unit apartment complex. You observe a similar existing complex that generates 330 trips during a 24-hour period. To find the daily trip generation rate:
Total Trips: 330
Independent Variable: 50 (Dwelling Units)
Calculation: 330 / 50 = 6.6
The rate is 6.6 trips per dwelling unit per day. This rate can then be applied to other developments of the same land use category in the area.
Why Accurate Rates Matter
Inaccurate trip generation data can lead to two major issues. Underestimating trips results in unexpected traffic congestion and safety hazards on surrounding roads. Overestimating trips can lead to unnecessary infrastructure costs for developers, such as paying for excessive road widenings or oversized signalized intersections.
function calculateTripRate() {
var trips = document.getElementById('totalTrips').value;
var quantity = document.getElementById('ivQuantity').value;
var unit = document.getElementById('ivUnit').value;
var resultDiv = document.getElementById('tripResult');
var rateOutput = document.getElementById('rateOutput');
var interpretationOutput = document.getElementById('interpretationOutput');
// Validation
if (trips === "" || quantity === "" || trips <= 0 || quantity <= 0) {
alert("Please enter valid positive numbers for both trips and quantity.");
resultDiv.style.display = "none";
return;
}
var t = parseFloat(trips);
var q = parseFloat(quantity);
// Calculation
var rate = t / q;
var roundedRate = rate.toFixed(4);
// Display
rateOutput.innerHTML = roundedRate + " trips per " + unit;
interpretationOutput.innerHTML = "For every 1 " + unit + ", this development generates approximately " + rate.toFixed(2) + " trips during the studied period.";
resultDiv.style.display = "block";
}