In message , Helen Deborah
Vecht writes

We actually caught up with the 302 that we'd missed.
Every 8-12 minutes could be more frequent than every 12 minutes.

But only if the buses are not running to schedule, since the exact
timetable at http://www.londonbusroutes.net/routes.htm indicates that at
the time of day concerned, buses leave Mill Hill at 12-minute intervals.

Off-peak buses often run rather faster than scheduled.

But there lies the rub - even if they leave on time, people later on the
route cannot rely on catching the bus they hope for if they run ahead of
schedule, whether such folk have used the journey planner or looked-up
the timetable. For instance, if each successive bus makes up 10 minutes
on the journey, the frequency at a stop near the end of the route could
end up with a 20-minute service interval instead of a 12-minute one.

My overall impression is that JP underestimates Tube journeys and
overestimates bus journeys.

It uses published timetables and I don't think it gets those times
wrong. But I think it creates more of a safety margin for buses - which
is perhaps understandable, given the state of London's roads.

Having said all that, I think it is inevitable that local knowledge and
personal circumstance can often beat the journey planner on bus
journeys.

For instance, from almost outside my house we have buses every 8 minutes
to Hammersmith tube station - but they start some miles away and are
therefore subject to delay. Only 3 minutes' walk away we have the
terminus of the number 209, from whence buses depart every 3-4 minutes
for the same destination - and, being the terminus, they mostly leave on
time. But which do you choose? I don't know - in whichever direction I
go I generally miss one or the other! Added to that is the fact that the
3-minute walk includes a steep climb over a railway bridge, which won't
suit everyone! I don't really see how the journey planner can cope with
quite this level of detail - it can only really be a rough guide.

--
Paul Terry