Changing start line

I would not remeasure course but would do the following...
Assuming the new "Start is on current course"
1) Need to be done before any roadwork begins.
2) Calibration not needed...
3) Do two rides recording counts between "New Start" and "Old Start"
4) Use highest count of the two rides assuming they are resonably close. Do additional rides if needed.
5) Divide hightest count by 2 to get counts needed to add to turn-around.
6) Ride from "old" TA to new TA by using the count in #5
7) Ride and record counts from new TA to old TA. Adjust new TA if second ride has few counts by the number of counts it was short.
8) For all mile markes before TA, move away from Start by the number of counts in #4

If new Start is not on course, then the net change would need to be computed and those counts used to adjust TA.

Same process in reverse could be used after roadwork is completed.

You will need to add length to Start or Finish (you didn't say if they were the same spot, so I will assume they are different locations).

Yes, you will have to re-measure from the road to the desired Start line, once the road is paved. You would do that in reverse - measure from this-year's turnaround to the old turnaround (twice), then use those counts to locate your new Start line on the new pavement.

Thanks Ken & Duane. That is sort of what I thought. But my next question is and I haven't been to the starting line yet but I have a feeling it might be all torn up already and if it is can I just go to the mile mark and measure back to the new starting line and then add the distance to the turn around point to make a mile.
1) Figure from start to 1 mile using prior rides and take the shortest count of the 2 rides to see what the distance of the mile mark would be.
2) ride from the mile mark to the new starting line (twice) and get the distance.
3) subtract the figure in step 2 from the figure in step 1. What ever is left over I would add to the turn around point to make the course the same distance.
Does this seem reasonable?

J.A., if the original Start is no longer accessible to measure to, you will have to re-measure the entire course, unless Mile 1 was a certified point. Most of the time we don't certify splits, as that would require adjusting them after two rides.

While one would believe that Mile 1 would be close enough for your method, the guidelines don't allow it, nor should they. There is too much uncertainty in the accuracy of non-certified splits, even though we believe they are within a foot or two of being precise.

You could certainly place the new Start using your stated method, but that would only give you a starting point for a complete re-measure. It is valuable information, but a certification can't be issued for an "adjusted" course if the original Start is not accessible. Sorry.

If Gene disagrees, he will let us know, and I will stand corrected.

Duane no the 1 mile split wasn't certified.
Let me ask you this what if I took from mile 1 to the finish for the 2 rides and come up with the shortest distance for the 2 rides. Than I could start at the 1 mile point and ride back to the new start and than add whatever distance I need to the turnaround to make it a half marathon distance that can be certified. This way I wouldn't have to ride the whole thing again if the road is all tore up.

Does the mile mark have to be officially "certified?" If I measure the first mile twice, and then put the mark at the shorter of the two measurements, then the mile mile mark is in the certified position, even though I didn't say the mile mark was certified on the map.
Following that logic, you could do this after the fact if you still have the measurement data. Use that data to figure out where the 1-mile mark certified position should be. This is essentially was J.A. is suggesting he could do.
All of this assumes though, that you have a good description of the original mile mark location, not just a paint line in the road and/or an approximate number of feet from a landmark.

Mark, I don't believe it has to be officially certified. If, as J.A. indicates, and you concurred, the original measurement data is available, and the split location can be positioned in the certifiable location, there is no reason this should not be considered proper.

If this is done, then a set of calibrated rides can be done to find the distance to the new desired Start line. Then, it is adjusting all the splits and turnaround points accordingly. Still lots of work, but likely less time than riding, unless the course is not entirely accessible by car.

Mark and J.A. - thinking outside the box makes this situation work. Way to go!

There is no sense in certifying the mile mark as it's not record eligible.

Working from an old mile mark is tricky. Unless the point is very well documented the possibility of getting the wrong point increases. This exact thing happened years ago. The measurer worked from a mile split and adjusted the new course from there. End result, recordworthy performances were achieved, the course was Validated and failed. The measurer and the race were mightily embarassed.