When trying to define Traffic Line Lanes using AASHTO LRFD, why is the Lane Width locked at 10ft when it should be 12ft?

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Answer:

According to clause 3.6.1.2.4 concerning the Design Lane Load, 




The design lane load of 0.64 kips/ft in the longitudinal direction has been defined for 10 ft lane width. To accommodate this clause, we have kept the lane width fixed at 10 ft. Having a proper design load according to code allows us to get precise results. Using this, standard vehicles have been created in Midas civil which could be used directly.