Ask-a-Cop: Following Too Closely

“I often drive to and from Brattleboro on Rt 30, and often see extreme examples of tailgating. I usually set my cruise control close to the speed limit. This often results in a backup of cars behind me, and sometimes the car behind me doesn’t honor safe stopping distances.

Do they still teach about stopping distances in Driver Ed? Is there a specific law against driving too close?

What’s your advice in a tailgating situation? On a road like Rt 30, it’s not practical or safe to pull over and let all the other drivers speed by.”

You have a couple of questions here.  First, let’s talk about driver’s education.  Yes, they still teach stopping distances and here is a refresher.  An average vehicle traveling 50 mph (the limit for most of Route 30) with properly functioning brakes will travel about 123 feet once the brakes are applied. 

Keep in mind, however, that cars are driven by humans.  A driver who is focused and paying attention will take about 1.5 seconds to apply the brakes when faced with an unexpected emergency.  That breaks down to about 1 second to perceive the emergency and decide to brake and another .5 seconds to actually lift your foot and apply the brake.  Remember, the 1.5 second response time is for a focused and attentive driver.  Any kind of distraction will significantly increase that time.

During this 1.5 seconds of reaction time, the vehicle continues to move at 50 mph.  It will cover about 110 feet during that time, making total stopping distance about 233 feet.  How many of us leave 233 feet between you and the next car in front when you drive at 50mph?

A few other numbers – total stopping distance (reaction and braking).
25mph = 86 feet
35mph = 137 feet
65mph = 356 feet

Here are some more fun facts for you math geeks out there.  When going 25mph, the reaction time distance is 55 feet and the braking distance is 31 feet for a total of 86 feet.  When going 50mph (twice as fast), the reaction time distance is 110 feet (twice as far) but the braking distance is 123 feet (four times as far!), for a total of 233 feet!

So why does the reaction distance simply double, but the braking distance quadruples?  The answer is math and physics. 

The distance traveled during reaction time is in direct proportion to the speed of the car – simple math.  However, when you actually apply the brakes, physics comes into play.  The braking system is working to create friction to slow down the speed of the car.  The two forces at work are friction (created by the braking system and tires on the road) versus kinetic energy (the movement force created by all moving objects).  The formula to calculate kinetic energy (k) is k = 1/2mv2

What does all this mean?  Reaction distance is in direct relation to velocity.  Braking distance is a function of v2, or velocity multiplied by velocity, which results in a number that increases exponentially. 

Now for the legal question.  Vermont law 23VSA1039 states in part:

§ 1039. Following too closely, crowding, and harassment

(a) The driver of a vehicle shall not follow another vehicle more closely than is reasonable and prudent, having due regard for the speed of the vehicles and the traffic upon, and the conditions of, the highway. The operator of a vehicle shall not, in a careless or imprudent manner, approach, pass, or maintain speed unnecessarily close to a vulnerable user as defined in subdivision 4(81) of this title, and an occupant of a vehicle shall not throw any object or substance at a vulnerable user.

If someone is tailgating you, the best course of action is to pull over and let them pass.  Route 30 can be treacherous, but in many areas there is a sufficient shoulder to pull over and allow this.  Feel free to obtain a license plate and description of the vehicle as well and contact the police with this information.

Regarding Route 30 generally, the Brattleboro Police have received a number of complaints from residents and commuters related to this road and Upper Dummerston Road.  Over the past few months officers have been deployed to this corridor exclusively for the purpose of traffic enforcement.  Dozens of stops have been made and many tickets written.  Hopefully this ongoing effort will make it a safer route to travel.

Thanks to BPD’s accident reconstruction team for help with this aswer.

If you have a question for the Brattleboro Police Ask-a-Cop, please email it to and put “Ask-a-Cop” in the subject line.

Comments | 1

  • Following distance

    Next time I’m behind someone I’ll get out my iPhone calculator and figure out velocity, momentum, reaction time, and all the physics so I can calculate the distance I’ll need to stop. 🙁

    What I usually do is allow a 3 second gap between me and a vehicle ahead of me. Simple, effective. I especially leave this amount of distance when I’m on my motorcycle. I also keep an eye on traffic behind me too, because THAT driver has to stop if I do! Gaps fore and aft give you a cushion of safety.

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