The Texas Congestion Index (TCI) is a measure describing how much longer a trip takes during the peak period ("rush hour") than it would when traffic is flowing freely. A TCI of 1.0 indicates there is no difference in travel time between peak and off-peak periods while a TCI of 1.35 suggests it takes about 35% longer to complete a trip during the peak period than it would in free-flow conditions. Put another way, if your daily commute to work takes 30 minutes when there is no traffic (say, midday or on a Saturday) and the road you travel has a TCI of 1.2, it will take an average of 36 minutes to make the same trip in the peak period.
TCI is a baseline we can use to compare levels of congestion across different kinds of roads in different parts of the state. In nearly all cases, actual congestion will be worse that what is suggested by the TCI because it does not take into account the traffic-slowing effects of accidents, construction, and other bottlenecks.