Definition of “Close” and Following Distance Guidelines
By “close” behind my truck I mean a distance less than the distance your personal vehicle travels in one second. For example if my truck and your vehicle were traveling at 60 miles per hour the “close” distance (risk zone) behind my trailer would be anything less than 90 feet (rounded up) or approximately 6 compact-size 14 1/2-foot car lengths. This threshold is arbitrary, not government-mandated. It is my way of advising a minimal time window to recognize and respond to any sudden action I may have to take.
One second is not much time to recognize and react to a sudden change in traffic flow. I feel your following distance should really be at least two seconds at speed (180 feet at 60 miles per hour or approximately 12 compact-size car lengths or approximately 2 1/2 big rig truck lengths). However, this is not always practical in light of current automobile performance and driver behavior in good weather and road conditions. At normal speeds on city freeways and other major highways in urban areas, drivers in personal vehicles routinely close to within one car length of each other and one or two car lengths behind a truck.
In bad weather and/or bad road conditions, you should of course allow more following distance. In winter there is an additional advantage to a longer following distance. Per a great message that I saw on the back of one trailer, stay back when you see snow or ice on the top of a trailer in front of you. This is because chunks of snow or ice blowing off can hit and damage your vehicle’s windshield or body if you are driving too close.
(NOTES: A common published guideline for personal vehicle drivers’ following distance is one car length for every 10 mph (miles per hour) of speed. At 60 mph this distance would again be approximately 6 compact-size car lengths. I prefer measuring following distance in seconds of travel as described above because it is a little easier to gauge your following distance by estimating in seconds how long it takes to reach some roadside object after the vehicle in front of you has passed it.
A general guideline for truck drivers’ following distance behind traffic in good weather and road conditions is one second of travel for every 10 miles per hour of speed. At 60 miles per hour this distance is 528 feet or one tenth of a mile. Another guideline is one second of travel for every 10 feet of truck length, plus one additional second for speeds over 40 miles per hour. With a tractor trailer length of about 75 feet, at 60 miles per hour this distance is 748 feet or a little less than one and a half tenths of a mile. Such distances are virtually impossible to maintain in heavy traffic—even if I hang back, drivers fill in the space in front of me.)
Though I may not detect you close and directly behind my truck, this zone should be less risky than others because theoretically you should be able to stay clear of any maneuver I might have to make. You in your personal vehicle can turn, slow down and stop more quickly than I in my truck. Nevertheless rear end collisions by personal vehicles and motorcycles do occur. The safety bar mounted on my trailer’s tail below its doors is there to keep your vehicle from sliding under the trailer in a rear end collision, thereby decreasing chances of critical injury, even decapitation. (Note that it might not work for a motorcycle collision.)
Other than preparing to pass me or merging into traffic behind me from an entrance ramp, I can’t think of any reasonable intrusion into this zone. In these instances you should still leave this zone as soon as possible. It is always better to keep a safe distance behind me. You might think you can save fuel by drafting me, especially in a strong head wind, but who wants to drive for any extended period of time so close to the rear of a truck that you can’t see anything ahead? In drafting close behind me, you may be lulled into a state of complacency and you are not allowing adequate safety margin in which to recognize an emergency and take evasive action.
The only instance where drafting makes some logical sense is in dense fog. I have had drivers draft me in fog in the apparent belief that I can see better than they and that I can “run interference” for them. In ground fog my angle of vision might be better than yours, but I make no guarantees. Especially in impaired vision conditions I advise hanging back and closely monitoring my truck to avoid rear ending it, should I have to suddenly slow down and/or stop.
I am limited in what I can do to help when you are following too closely. First, I need to detect you. If you swing out from directly behind me to one side (preferably my left side), I may see you in my large side mirror and/or in the small convex mirror below it. Failing that, in daylight the only way to know you are in that zone is to see the shadow of your vehicle in one of my side mirrors. At night I may notice the ambient (scattered) light from your headlights if we are not driving through a city or other well-lit area.
To help you and other drivers when I’m preparing to change lanes or exit a highway or interstate, I can usually signal a long enough time to give adequate notice. On multi-lane highways and interstates, I often signal then hesitate to let drivers close behind me pass before I pass another vehicle. I have to be especially careful in finishing a pass on the left that an impatient driver behind me does not “jump” me in the lane to my right before I can return to it. Truck drivers and some drivers in personal vehicles help by signaling me over as soon as my truck clears them so I can get out of the way of faster vehicles. (We will detail these and other maneuvers in the Passing You chapter.)
In some situations on a two-lane highway I slow down to let you pass more easily, but bear in mind that my job is to drive as fast as I can safely and lawfully. My truck’s top cruising speed is limited to 65 mph (miles per hour). Your personal vehicle can usually accelerate past me safely and lawfully. My truck loses significant momentum when I slow down, and it takes time and extra fuel to get back to my former speed. So to enable you to pass without help from me, I would rather wait for some traffic or road condition such as a traffic stop light, a grade that my truck will lug down on, a passing lane or a straight stretch of highway cleared of oncoming traffic. (I do watch your pass closely in case I have to slow down to let you in front of me before oncoming traffic arrives.)
You are in a risk zone when you follow a truck at less than the distance your vehicle travels in one second.
This risk zone may not seem as hazardous to you as others because your personal vehicle can turn, slow down and stop more quickly than a truck.
However, it is still safer to stay at least 2 seconds of travel behind a truck unless you are in the process of passing it or merging behind it from an entrance ramp.
Increase your following distance in bad weather and/or bad road conditions or if you see snow or ice on top of the trailer in front of you.
As a general rule, move out of all risk zones around a truck as soon as it is practical, safe and lawful to do so.