The expansion rate is the rate at which the field round time gets longer throughout the day or tee block time slot.
We enter the course at the tee time interval e.g. 7 or 8 minutes. We would like to exit the course at the same interval. This would bring the last group of the day in with the same round time as the first group. But this is not always possible and should not always be expected.
So what is an acceptable expansion rate?
If a tee block contains 13 tiers and the expansion rate is 1 minute, the last group will experience a round time 13 minutes longer than the first group. If the first group finishes in 4:10, the last group will have 4:23. If a 2 minute expansion is experienced, the last group will have 4:36. So we can see that we are getting pretty long times if we accept a 2 minute average expansion rate.
Of course the first group may be faster than the policy time 4:10. But since this is the policy we should always measure the total expansion in time after assuming a policy time from the first group. That way we can be consistent.
The graph above shows the individual expansion rates of each tee block for the day (lines) and the average across the tee blocks for the day (bars).
The graph shows that it is possible to have negative expansion rates. It is indeed possible to have groups coming off the course faster than the 8 minute tee time they use to enter it.
Generally, though, a 1-2 minute expansion rate is typical and that’s where we would like to see it. This graph tell us that the last groups in the field are not being unduly delayed throughout the day.