Are you saying that a features has one attribute for lane number and another attribute for lane length? If this is correct, you could use AttributeManager or AttributeCreator to create a new attribute that is the some of the lengths. If there are a different number of lanes for different features then you will have to handle null or missing values.

Are you saying that you would like to add all of the lengths for lane 1 together, and then the same for the other lanes? The StatisticsCalculator will do this.

Thanks for the solution, it works​