Source: The TomTom Traffic Index The TomTom Traffic Index is based on real travel time data captured by vehicles driving across the entire road network. TomTom's traffic database contains over nine trillion data measurements. The Traffic Index compares travel times during non-congested periods with travel times during peak hours. Cities with the highest rankings in the index experienced the sharpest increases in travel times between non-congested periods and peak periods. Cities in Asia were not included in the index due to insufficient data.