Facts Examination

Speed Trap, Highway 58 Lacrosse, VA

By Rachel Hallgarth (NASA Scientist, Ret.)

 

Highway 58 ‘Pacing’ Claim:

Police Impossibility!

This analysis is being done at the request of Mr. Scott Colley. Not knowing the mass or specifics of the police vehicle I am only guessing about its acceleration rate once on the highway chasing Mr. Colley.

This incident happened on Highway 58 in Virginia at night and the total distance traveled is approx ½ of one mile or 2640 feet. We are going to assume the police vehicle is rather quick and can accelerate at a constant rate of 10 mph per second or 14.6 f/s acceleration. Acceleration of a vehicle is not constant because of drag and power to weight ratio be let us assume the good officer had a quick ride.

There are some other assumptions that need to be made and they are.

1. The police vehicle required a certain time frame to start moving and turn left onto the highway. We are assuming the officer just went and turned and since he was sitting off the road it is reasonable to assume it took him 3-4 seconds to get turned onto the road and straight enough to accelerate rapidly.
2. Mr. Colley was moving at a constant rate of speed of 50 mph in the 50 mph speed zone after he reached the speed zone.
3. The officer began his move to pursue Mr. Colley when Mr. Colley was 150 yards past him since the officer was stationary and assuming Mr. Colley’s car was traveling at 40 mph it would have traveled some distance before the officer could even move.
4. The entire distance traveled by Mr. Colley was ½ of a mile that has been verified by video.

 

I am going to ignore the officer admission that he was 150 yards behind the Colley car when he began to move which is even more damning.

40 mph is equivalent to traveling at 59 feet per second. At 40 mph as Mr. Colley passed the officer he was traveling at 58.7 feet per second. So at 40 mph in one minute Mr. Colley would travel 3520

It would take a minimum of 2 seconds for the officer to believe he needed to tail this driver to get an average speed to ticket him unless his mind was already made up regardless. This puts Mr. Colley approx 118 feet down the road before the officer has even begun to move.

It would take at least another 3 seconds for the officer to get the car in gear, turned and in pursuit of Mr. Colley at let us say 10 mph when he is straight. Mr. Colley has now traveled an additional 177 feet and is now accelerating to 50 mph the new speed limit. 

Mr. Colley is now 295 feet down the road as the officer starts accelerating from 10 mph to a pursuit speed of 65 mph. Assuming the officer’s car accelerated like a Mustang at about 10 mph per second he is accelerating at 14.6 feet per second for 5.5 seconds to reach 65 miles per hour.

During these 5.5 seconds Mr. Colley is now traveling at 73.5 fps so he traveled an additional 404 feet and is now at 700 feet.

During this time the officer is accelerating he travels a distance based on the following physics formulas:

Distance = ut + 0.5at^2 where us is starting velocity in fps multiplied by time

a == acceleration rate of  14.7 f/s 

t is time of 5.5 squared

so (14.7 x 5.5) + 0.5 * 14.7 * (5.5 x 5.5) the officer traveled

229 + 222 or 451 feet, which leaves him 250 feet behind Mr. Colley.

He would need to begin matching his speed to Mr. Colley’s speed which would take at least 10 seconds which would mean Mr. Colley traveled an additional 735 feet and is now at the 1400 foot mark.  The officer by law must follow for a specified time, which I am unsure of but we are currently closing in on the 2640 feet that this event happened over. If we add the officer admission that when he pulled out the officer was 150 yards behind Colley it is even more damning and this is with the Colley car obeying the speed limit. With this distance we are at 1750 feet give a take a bit.

In reality the officer could ONLY have caught Mr. Colley if Mr. Colley was in fact going the speed limit and in fact he barely caught him and had no time to actually time him, turn on his lights and pull over Mr. Colley in the 2640 foot distance.  The minute you plug in that Mr. Colley was going 65 mph it is physically impossible for the officer to have caught him, follow him, and validate his speed in 2640 feet.

65 mph is 95.5 fps

Recalculating the numbers is enlightening if Mr. Colley was actually speeding.

By the time the officer has reacted Mr. Colley is 286 feet down the road. By the time he is turned and started and straightening out Mr. Colley is now 572 feet down the road. If he accelerates to just 65 mph he is 5.5 * 95.5 or 525 additional feet so Colley is at almost 1100 feet and the officer has traveled his 451 feet and is nearly 650 feet behind Mr. Colley in the dark or to be more clearly almost 1/8 of a mile. There is no way to judge the speed of the other vehicle from that distance unless it is done over a significant distance. The California Highway patrol used this methodology for many years and they required vehicles this close to the actual speed limit to be followed for a least a mile or longer to obtain an accurate speed unless the speed was insanely over the limit

In the dark it would take a significant amount of time to equalize speeds and be sure the driver is going too fast. The officer would need to close the distance to a more manageable distance where he can maintain or match the speed of Mr. Colley.

Since the officer is attempting to pace the Colley car for speed it needs to be done over a reasonable distance. It is not possible to judge the speed of a car 1/8 of a mile from a car following another car because it is difficult to determine whether you are closing on the vehicle in front of you at that distance. The officer must keep the exact distance of 650 or any calculation he makes is wrong. If the officer was closing at 22 fps he is going 15 mph faster than the car in front of him

At the speeds the officer claims they were both going it is visually impossible for the officer to get an accurate measure of the Colley vehicle speed since the Colley vehicle has already traveled 1100 feet of the proven 2640 feet used in this incident and they are now both traveling at 95.5 fps but the officer is so far behind there is no accurate way he can judge speed in the ten seconds he had to perform this analysis because at that point his lights were flashing and he pulled the Colley vehicle over at slightly less than ½ mile.

It appears the officer made his decision rather quickly and in my estimate in less than 5 seconds. During the decision process at night he could have easily moved from 650 feet to 540 feet with little perception of being closer since distance at night is skewed by darkness and the fact the distance is judged not by the entire vehicle but by the tail lights and what little of the vehicle is illuminated by tail lights.

Humans use stereoscopic binocular vision to determine distance and it deteriorates at night in low light and based on the movie it was pitch black. To the human eyes in the dark a set of taillights cannot be followed keeping an exact distance because the human eyes uses this stereoscopic binocular vision based on size, and location, and lighting and both size and lighting are poor in this case. It is impossible to be 1/8 of a mile behind someone in the pitch dark of night and use taillights to judge distance between two vehicles. This requires good vision by the way and the officer was wearing glasses, which again could skew his perception of distance under these conditions.  I wonder when his last eye exam was.

Based on pure physics and the stereoscopic binocular vision we humans possess and its limitations in the dark this traffic citation is impossible to support under any circumstances.  The simple facts are the only way the officer could have caught and even attempted to tail and clock the Colley car in the distance traveled was if the Colley car was in fact going the speed limit.

Rachel Hallgarth

NASA, Retired

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