Until the spell ends, when you use the Dash action and move at least 30 feet in a straight line, you leave behind a 5 foot wide streak of lightning that lasts until the start of your next turn. The streak originates from the space in which you began moving in a line and stops if you turn (i.e if you moved 20 feet then turned and moved 30 feet in a line then turned and moved 10 feet, it originates from the point where you first turned and ends at the point where you turned again). If you move 30 feet in a line then turn and move another 30 feet in a line, the first streak dissipates, leaving only a streak from the second path travelled.

While moving in a straight line, you do not provoke attacks of opportunity and can move through other creatures’ space and it does not count as difficult terrain. If you end your turn in another creature’s space, you take 1d8 Force Damage, you are shunted to the last unoccupied space you occupied, and the spell ends early. Each creature that starts or ends its turn in the lightning streak takes 2d12 Lightning Damage. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d12 for each slot level above 2nd and the lightning streak counts as difficult terrain for other creatures.