Wonder if the constant vibration from the interstate above got to it?
Interstate highway pipeline crossings are usually cased in a larger heavy wall pipe.
You will normally see the vent pipes on each side of the road.
The problem is many of the original crossings had problems with shorted casings which prevented the corrosions systems from protecting the internal pipe when the casings flooded. It usually takes a fairly qualified engineer to interpret the data to find the problem.
There are remediation methods, however it is a problem that is regularly missed. Just a preliminary interpretation of the possible issue involved.