About Traffic Indices At This Website

Traffic Index is a composite index of time consumed in traffic due to job commute, estimation of time consumption dissatisfaction, CO₂ consumption estimation in traffic and overall inefficiencies in the traffic system.

Time Index - is an average one way time needed to transport, in minutes.

Time Exp. Index - is an estimation of dissatisfaction due to long commute times. It assumes that the dissatisfaction of commute times increases exponentially with each minute after one way commute time is longer than 25 minutes.

Inefficiency Index - is an estimation of inefficiencies in the traffic. High inefficiencies are usually caused by the fact that people drive a car instead of using a public transport or long commute times. It can be used as a traffic component measurement in economies of scale.

CO₂ Emission Index - is an estimation of CO₂ consumption due to traffic time. Measurement unit is grams for the return trip. To calculate an average estimation of emission in grams for one way commute to work, divide this value with 2.

Actual formulas to calculate indices are subject to change and at this moment, quite complex empirical formulas are used. Those formulas as written in the Java programming language are as follows:

  protected void calculateIndex() {
    index = new TrafficIndex();
    index.time = overall.getTimeOverall();
    double tooMuchTime = 0.0;
    if (index.time > 25.0) {
      tooMuchTime = index.time - 25;
    }
    index.timeExp = index.time + Math.pow(tooMuchTime, Math.E);
    double co2 = 0.0;
    co2 += overall.time_bus * 20.0; // bus produces 20g of CO2 per minute (for each passenger)
    co2 += overall.time_driving * 133.0; // car produces 133g of CO2 per minute (assumes only driver)
    co2 += overall.time_train * 10.0; // train produces 10g of CO2 per minute (for each passenger)
    co2 += overall.time_tram * 15.0; // tram produces 15g of CO2 per minute (for each passenger)
    co2 += overall.time_other * 10.0; // other produces 10g of CO2 per minute
    co2 += overall.time_motorbike * 80.0; // motorbike produces 80g of CO2 per minute
    index.co2 = 2 * co2; 

    index.main = index.time + Math.sqrt(index.timeExp) + Math.sqrt(index.co2) + Math.sqrt(index.inefficiency);
}

To estimate number of trees to cover CO₂ consumption, we assume 240 days of commuting during the year and we are using the cite "A single tree can absorb CO2 at a rate of 48 lb. per year." - Arbor Enviromental Alliance.
As java formula formula:

    double co2CommuteConsumptionYearly = 240 * index.co2;
    double treesNeededForCommute = (co2CommuteConsumptionYearly / 1000) / 21.77;  //each tree absorbs about 21.77kg of CO2