Instrumenting pavement with fiber optic sensors has recently gained popularity as a part of the digital infrastructure transformation. In this survey, we present some of the recent real-world implementations of fiber optic sensors as real-time traffic monitoring systems. We highlight advantages and limitations of the surveyed instrumentations. We identify preferred range of values for some of the key design parameters that are necessary for durability and accurate weighing of individual axles. These parameters include strain resolution, scanning rate, installation depth, spatial resolution, and sensor orientation. Some of the studies report excellent results in terms of vehicle axle count, weight, and speed achieving accuracy levels above 90% with single digit margin of error. Lastly, we draw attention to some of the outstanding challenges from technical, operational, and scalability points of views.