This overtake is very well-known in
Japan's trainspotting world.
Keikyu deliberately designed that section of the route to be as
fast as possible and a timetable as such that it lines up with the
JR train's timetable - that it will always overtake and hence
demonstrate that it is faster than JR.
Talking of which they always get the load when the Tokaido Line
is down due to signal and passenger accidents... 
So, it is basically saying that "SBST"'s trains are faster than
the "SMRT"'s trains (Too bad our MRT trains have no similar lines
running in parallel / same lines running in different tracks as of
yet)
PS: Does the 2 tracks connected such that the JR train can come
over to Keikyu and vice versa?
Keikyu is on standard gauge (1435 mm) while JR is on Japanese
Narrow gauge (1067 mm).
What I would like to add on to folks who are in awe at the Ginza
Line timetable, I must remind that there are areas in Japan where
there are only one or two trains (for example, Iwazumi Line in
Iwate Prefecture) per day on the line. Why so few? It all down to
utilization.
I believe that its not the first time I brought up this topic
when it comes to transportation. Places where there are a lot of
commuters, service have to be upped. But this does not mean upping
the entire network's frequency. How about up s975's frequency when
adding buses to s190? Not sensible right.
Japan has a network of strict utilization and hence where its
busy, trains run frequent, where it is less utilized, services will
be cut.
How does it relate here? Well, you gotta weigh out the places
that are running empty buses and trains and places where its packed
like sardines. Frequency is one thing; the amount of people taking
them is another. However it is in responsible systems that we see
tight schedules coupled with packed trains, loose schedules with
well, a fully seated transport.
