This is based on two courses, not the new short-short -- I don't know where the timing lights will be on that one. But --
on both of the traditional long and short courses you must run two miles before you get to the first timing light. The next light is at the 2 1/4, as Glen has correctly said (all of his information is correct). The following light is at the three, then the four, then one light 132' before the five and the last one at the five.
The stretch of salt from the 2 to the 2 1/4 is timed for only one (basic) reason -- to determine if the vehicle is qualified to run the long course, and that qualification is accomplished by having a speed through the quarter-mile-long stretch of 175 mph.
The first full mile -- is from the 2 to the three. That stretch of the course is the first place where your speed can be used for a record -- all SCTA/BNI records require speeds to be measured over a flying one mile. The racer may elect to turn off after the lights at the three mile marker and still have completed a run -- and still be eligible for a record, assuming his speed was above the existing record speed. The mile from 3 to four can be used for a record, and ditto from the four to the FIVE. The trap at the end of the five is "terminal speed", and is useful (as others have said here) for some, such as the heavy/fast vehicles that are still accelerating after five miles of run...so those vehicles can see the speed and make choices about gearing, etc. But the timed trap speed is unofficial (although just as accurately measured as any other speed) for record-setting purposes. As an example of "still accelerating after five miles" -- the Burkland car ran 415 and change in the last mile, but the exit speed was 403.99 or so. This implies Tom entered the last mile at something like 400 and gained 30 mph during that mile.
As for the new short-short course -- I think (note my caveat) that there is a timing light at the 1, at the two, at the 2 1/4, and at the three. The timed quarter mile is still in the traditional location -- and the timed first mile is a legitimate mile for record-setting purposes, such as the small-engine bikes that have a terminal speed in the double-digit range. Those hit top speed in a half-mile or so -- and no matter how long you hold the throttle pinned, the bike doesn't gain any more. Turn off after the first timed mile (which, in this case, would be the second mile from the start line) -- so the other competitors don't have to wait 'til darn near suppertime for you to finish your run.
How'd I do, Glen?
