It is a four-lane divided highway for 7.6 miles (12.2 km) from LA 30 eastward to an intersection with Highland Road and Siegen Lane in southeastern Baton Rouge.

[1] From this intersection, LA 42 turns east and follows Highland Road to US 61 (Airline Highway).

In this segment, it passes the Highland Road Park and Observatory and the Louisiana Country Club.

Curving to the northeast, LA 42 widens to four lanes and passes through an interchange with I-10 (exit 166).

[1] As of 2018, the portion west of US 61 is under agreement to be removed from the state highway system and transferred to local control.