Quote:
Originally Posted by roflwaffle
The problem w/ a ~125-150ft interval IMO is that it can take ~130ft before someone even starts to slow down. |
If you are 130 ft behind a vehicle that begins braking and it takes you 130 ft to react and begin braking as well, you will begin braking at approximately the same point as the vehicle in front of you, if you have better braking capability or shorter stopping distance you will still be well behind that vehicle when stopped as the vehicle in front of you will be incapable of an instantaneous stop (except in the instance of something influencing the abrupt stopping of the vehicle in front of you such as the already mentioned reinforced wall, car hitting a stopped big rig, etc).
Assuming that average human reaction time from seeing a situation to applying brakes takes 130 ft, I'd say that 130+ ft is safe for a following distance. Of course that distance will vary with speed, so basing your folowing ditance on something fixed like time will allow your distance will vary appropriately. 3 seconds following distance generally considered safe (the "three second rule"). By my calculations, at 70mph you can cover 100 ft per second, putting your safe following distance at 300 ft or 100 yards (a football field length minus the field goals). At 55mph that is reduced to 240 ft or 80 yards.
I have drafted big trucks before, and have seen significant gains in efficiency. Once I drafted a typical big rig with a box trailer, can't say the exact following distance as I'm not good at guessing distance in numbers but a good number of car lengths back. I had a 2000 Honda Insight at the time, 5-speed, A/C off, driving from west Texas into New Mexico drafting the truck at 55 mph for half the drive, the other half solo and I average 74.6 mpg and easily put around 600 miles on a single tank. I was stopped at a border checkpoint station where most cars were simply waved through and suspicious ones stopped, just so the guys could check out the car and ask questions about fuel economy. In normal everday driving I would typically get 52-56 mpg and when really trying being able to get up to 60-62 mpg per tank.
The Insight was replaced with my current 2006 Prius, which I have drafted an big rig that had an oversized load, it was just the perfect drafting truck, it had some odd shaped object on a large and very low to the ground flatbed that was all tightly wrapped in white plastic and the back end of the object had a nice taper and because the trailer was so low the ground there was little chance of any rocks or other objects getting thrown and it was going rather slow at about 55 mph heading east on I-10 from San Antonio to Houston, I was able to draft it for nearly the last half of the drive into Houston (mind you the entire distance is gradually downhill to the gulf coast) averaging just over 60 mpg where I normally average about 56 mpg.