Let me tell you a few concepts first:
1. The total span length is the sum of the clear spans of each hole in a porous bridge.
2. The clear span is the clear distance between two adjacent bridge piers (or abutments) at the design flood level.
3. The bridge length is the distance between the rear end points of the side walls or splayed walls of the two abutments at both ends of the bridge.
Then:
The difference of these few meters lies in the size of the pier body.
What’s next:
I guess you are confusing the concepts of net span and calculated span.
What’s next:
I’ve worked overtime and still typed so many words for you. If you understand, just accept it. Ha ha.