—The lack of vehicular traffic suggests a route not under heavy use by the Russian military and therefore a target of limited military value.”
The rail lines are one of two primary routes into Ukraine.
It is a big deal.
Daily traffic 15,000 cars
with bridge traffic peaking in the summer months – on 5 August 2018 the bridge broke a single-day record for car traffic, with 32,000 vehicles crossing the span, followed by over 33,000 vehicles on 12 August that year and over 35,000 a year later.
https://en.wikipedia.org/wiki/Crimean_Bridge
Scanning and searching each vehicle may slow the flow.
35,000 vehicles per day is not much.
In New Orleans, The Huey P. Long bridge and I-10 Twin Span Bridge are essentially the same transportation artery crossing the Mississippi river. The bridges share a common point on the New Orleans side and separate only 1.75 miles on the Slidel, LA side.
The Huey P. Long bridge carries over 50,000 vehicles per day. https://www.johnweeks.com/river_mississippi/pages/lmiss16.html
The 1-10 Twin Span Bridge carries 55,000 vehicles per day.