whether the front end of the car crossing the bridge is straight or arc refers to whether the intersection of the front end of the car and the bridge deck is straight or arc.

if it is a straight line, it means that the intersection of the front of the car and the bridge deck is a straight line, and this design is usually called a "straight bridge". If it is curved, it means that the intersection of the front of the car and the bridge deck is curved. This design is usually called "arch bridge".