Allocating vehicles to times

Hi guys, I am not sure where this question belongs. I have a problem in finding a suitable formula, etc for my problem. My problem is as follows: I have a timetable for trips departing every 5 minutes from point A to B. Each trip takes say 15 minutes and the vehicle then returns back to A for a next trip (also say taking 15 minutes to return). How do I set up a formula to allocate vehicles to the various trips to determine how many vehicles will be required to service such a timetable? Currently I do this by hand (as it is not cost efective to buy any scheduling software) but thought that Excel is so powerful and that there must be a way to do this automatically. I thought that it is almost a FIFO problem but cannot get to a satisfactory answer. Can somebody assist?

Hi
I don't think we have enough information. What do you mean by 'allocate vehicles to a trip'.

A de minimus solution is simple. A round trip of 30 minutes ignoring any change round time, requires 6 vehicles if each vehicle is 5 minutes behind the one in front. But I guess you have something else in mind.

Rgds

Hi Richard, thanks for the reply. The "allocate vehicles to trips" actually means allocating a vehicle to a time slot of a timetable (eg called a "trip" or "departure").

I attach a spreadsheet with an example of a time table between A and B and reverse on a specific route. A change round time of at least 5 minutes must be allowed for between arrival and departure. I want to calculate how many vehicles will be required to service this time table efficiently. As said in my previous post, it is done by hand but when you get a time table with frequencies of 2-3 minutes between the departures (on 20, 30, etc individual routes) it can get more complicated to do by hand and I need a quicker way to do it.

Thanx for your assistance.

Dan