# Reply To: Frequency and the 20 min rule

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#13885

So in the 66s image means a vehicle will pass every point on the the line every 66s. In this case we have only 1 vehicle so it takes 66s to go from Stop 1 back to Stop 1. But also 66s from Stop 2 back to Stop 2. Or 66s from where the mouse is back to where the mouse is – start a timer. That vehicle makes one loop of the line every 66s.

Now if I add a 2nd vehicle each one will do a loop every 66s but because there are 2 – a vehicle will pass every point every 33s. So Stop one will have a vehicle every 33s, Stop 2 will have one every 33s and where the mouse is will have a vehicle pass every 33s. (66 / 2 = 33)

6 vehicles will make it 11s (66 / 6 = 11). etc.

So yes the reverse works, if you have 6 vehicles and the frequency is 11s – then you know that one vehicle does a loop of the line in 66s. (11 * 6 = 66)

I think you need to forget about the individual stops, it’s nothing to do with them – every point on the line (maybe think of it as a circle) will have a vehicle pass every frequency seconds. (assuming equal spacing)

Does that make sense?

What I understand the guide try to tell is, you take the number of busses and multiply by the frequency to get the TOTAL travel time.

Yes if you want to travel a full loop of the line – frequency has nothing to do with travel time of a passenger as I understand – it is waiting time at a station. But you can calculate the total time to do a hypothetical loop.

It’s best to think of frequency as the maximum time a person has to wait (at any station as I’ve shown above they’re all the same). The travel time is calculated while the person sits on the bus. But what the guide is trying to say in a complicated way is that from the frequency you can find how long it takes to do a loop of the line. Number of vehicles * frequency (as I showed above is 66s in that case).

So looking at the line in our example (with 6 vehicles) you can say that the maximum waiting time for a vehicle is 11s (the frequency) and the maximum travel time is 66s (6 * 11) if the person wishes to come back to where they started.