  We present an algorithm to identify days that exhibit the seemingly
paradoxical behaviour of high traffic flow and, simultaneously, a striking
absence of traffic jams. We introduce the notion of high-performance days to
refer to these days. The developed algorithm consists of three steps: step 1,
based on the fundamental diagram (i.e. an empirical relation between the
traffic flow and traffic density), we estimate the critical speed by using
robust regression as a tool for labelling congested and uncongested data
points; step 2, based on this labelling of the data, the breakdown probability
can be estimated (i.e. the probability that the average speed drops below the
critical speed); step 3, we identify unperturbed moments (i.e. moments when a
breakdown is expected, but does not occur) and subsequently identify the
high-performance days based on the number of unperturbed moments.
  Identifying high-performance days could be a building block in the quest for
traffic jam reduction; using more detailed data one might be able to identify
specific characteristics of high-performance days. The algorithm is applied to
a case study featuring the highly congested A15 motorway in the Netherlands.
