Tailgating time/distance guide

While it is fairly clear from this that the Marten big-rig is way too close to the pickup, it is true that shots from angles like this tend to foreshorten distances and make vehicles look even closer together and it's sometimes hard to judge accurately.   How do we quantify it, especially for use in a report?   Here's what to look for.

visual guide to tailgating distance, Marten truck

The vast majority of highway lane stripes are painted in standardized length cycles, where the combined lengths of a stripe and the gap to the next one adds up to just about 40 feet.   The stripe length itself can vary a little, from 10 to maybe 13 feet, but they all start at regular 40-foot intervals.   This standard is used all over the country and is easily verified from satellite views of roads in any given area.

This serves as a convenient ruler for determining vehicle spacing in both distance and time.   60 MPH is about 88 feet per second, or a little over two full lane-dash cycles per second of distance.   Vehicles using the popular [but still insufficient] "two-second rule" at normal highway speeds should thus have at least FOUR full lane stripe intervals between them, and advisably more since most of them are likely moving at well over 60 MPH.   Leaving three seconds of space -- six lane stripes -- gives more margin to accomodate momentary distractions and more room for other vehicles to maneuver as they need to.   For heavy vehicles like trucks, popular training courses advocate at least five to six seconds of following distance which we almost never see in real life as soon as traffic begins to pack up even a little bit.

The numbers above verify the stripe spacing.   (1) is near the rear of the trailer.   (2) is the next 40-foot interval, at the same visual point in the next lane stripe, and (2a) marks the corresponding distance along the trailer.   The trailer is 53 feet long, and eyeballing (2) plus another estimated 13 feet to the nose of the trailer confirms that these are standard lane stripes.   A full sleeper-cab rig is 75 - 80 feet long and occupies most of two stripe intervals, thus between (1) and (3) here.   With the right sun angle, vehicle shadows can often make lining these correspondences up even easier.

More importantly, from (3) near the nose of the cab to (4) at the rear of the pickup can now be determined as about 50 - 60 feet.   That might sound like a healthy distance and looks fairly generous when viewed from above, but it is less than a second while we're all barreling up I-81 here.   When the pickup blows a tire and rapidly slows down, it will take about half a second for the truck driver to attain meaningful braking power *if* he's paying attention, after which there is very little margin left to bring the closing rate back to zero.   In other words, the pickup is toast and the Marten driver is 100% at fault.

If the truck's nose was behind the stripe at (1) that would give two seconds, which in this situation is still unsafe.   Ideally none of the Marten rig should be seen in the picture at all.   Granted, the polite course of action is for the pickup to move to the clear right lane as the rig approaches, but it's not up to the Marten driver to try forcing that with hazardous practice which was indeed the situation happening here.   If a supposed professional can't deal gracefully with traffic, he shouldn't drive.

As a safety manager at FedEx so aptly put it:   one has to ask the Marten driver and anyone else who behaves like this -- what if it's your parents or girlfriend in that car ahead of you?

[Photo:   2010 roadtrip, part 12]