Specifying the traffic conditions (if you're looking to override the default ETAs) and Calculating Route ETAs with Traffic Included can be done in Configuration ⇒ Optimization⇒ ETA Calculation.

Next to the ETA Scaling Factor, there is the option to input a number that shows the number of times the traffic is faster or slower compared to the one calculated by eLogii.

If the traffic is twice as slow, input 0.5. Vice versa, if it is twice as fast, input 2.

Also possible is selecting any of the options available and the number will change accordingly.

Click Save once the parameters have been set.

Including the traffic factor in ETA calculation can be done in Configuration ⇒ Optimization⇒ ETA Calculation., right above the ETA scaling options.

It's important to note that Live traffic & ETA updates apply in real-time for the current date and day, not for the next day. This means that It doesn't apply today's live traffic metric to tomorrow's planning data.
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If you disable Calculate route ETAs with traffic included, the Routes won't be calculated with traffic included and the optimization doesn't use the last known traffic data as default.

Click Save once the feature has been enabled.