
MK6

check the mile markers on a highway and for every 60 seconds one goes by,  you're going 60 mph. 

Conductor Budgie

One way is to reference the tachometer (engine RPM gauge) to a previously determined point. NASCAR stock cars aren't equipped with speedometers, so during the pace laps of the race, the pace car travels at exactly the pit road speed limit (usually 3555mph), and the cars see where the tach is at this speed (ex. 3500 rpm in 2nd gear).
Another way is to time yourself between mile markers. A speed chart follows:
Time per mile = MPH
36 sec = 100
38 sec = 95
40 sec = 90
42 sec = 85.7
45 sec = 80
48 sec = 75
51 sec = 70.5
55 sec = 65.5
1 min = 60
1 min 5 sec = 55.4
1 min 12 sec = 50
1 min 20 sec = 45
1 min 30 sec = 40
1 min 43 sec = 35
2 min = 30
2 min 25 sec = 25
3 min = 20
4 min = 15
6 min = 10
12 min = 5
15 min = 4
20 min = 3
30 min = 2
1 hour = 1 

humanresourcesman

Watch the mile markers on the Interstate Highway. Time how long it takes you to go from one marker to the next (i.e. from 245 to 246 for example). If it takes you exactly one minute to go one marker (one mile) then you are going 60 miles per hour (because there are 60 minutes in an hour). If it takes 30 seconds then you are going 120 miles per hour. If it takes 2 minutes then you are going 30 miles per hour, and so forth. 

Mark

If you drive fast enough, soon a friendly police officer will stop you and tell you how fast you were going. 

Pork

Highspeed camera 

Frankie

drive it on a deserted airport landing strip and see how fast you can go.. 

Iam!!

When you pass the first mile sticker, or some other markers that you know are exactly one mile, you begin counting oneone thousand, twoone thousand. Keep counting until you come to the next marker. When you come to that marker, it will tell you how fast you are moving. If you count to seven one thousand, you are doing 70 mph. This is how the Highway Patrol explains it, or other accident investigators determine rate of speed. 

Ricvee

If your car has a revcounter (measures the number of revolutions the engine does per minute) and you know from past experience (i.e....before the speedo failed !) at what speed the car engine is doing various revs,you can determine your speed. For example : I know that my car's engine does 2000RPM at 60Km/h in 4th gear, 2500RPM at 100Km/h in 5th gear and 3000RPM at 120Km/h in 5th gear... 

joelgmt

just keep going faster and faster, eventually a police officer will let you know. 

shadeofwild

speed gun or
Calculate by the dist / time taken 

larryboy

obviously these answers are not good because there in no way for you to measure your velocity or momentum, you cant really buy a radar gun to use on yourself or even find a cheetah. the only sensible answer here is to watch the mile markers. but still that would be dificult. you cant go the speed of traffic all the time cuz they are often well above the limit. if your spedometer is broken then get a new one. your state probably doesnt allow cars without spedometers on its roads so that is reccommended highly uncase you get pulled over by a cop. then youd be in big trouble if you didnt have one. so get a new one if yours is broken, and/or have someone check your old one at a mechanic. they can tell you to what degree yours is off. good luck and please remember always give larry boy best answer points!! 

randyrich

Past experience 

hpc91

Step on the gas... when you see red and blue lights behind you, you know you're going too fast! 

Nyx

I did this at high school:
Distance x time = speed
Thats just one of the stuff that I bothered to learn in science, did it for homework. (That is why I don't want to be a traffic warden) 

FAA

Drive a known distance and time you trip.
Distance/time gives the speed. 

Volleyballâ™¥Country Musicâ™¥Amanda

Velocity times momentum equals excelleration.
(V*M=A)
Physics. 

lparker_2005

radar gun or follow speed of traffic 

Lionel M

use a stopwatch when you accelerate turn it on when you stop then stop the watch 

MiaDiva28

i guess that comes from experience. if you've been driving for a while then you will know about how fast you are driving. if not then go with the speed of traffic. sometimes they have those scanner things on the side of the road that tell you how fast you are going. 

Claude

Look at the whit lines on the road.. if thy pass you slowly, it means you are moving slowly but if they are moving so fast that they almost look like 1 solid line with no braks then you are probably going fast!! hahaha!!! just kidding!
I would honestly say calculate the distance travelled & the time in which you have travelled. that will give you the km/h or mph but that will only give you th average speed and thats after you have done the trip. Im sure there must be other ways that I cant think of at this moment cos Im acting like a daft cow due to the lack of sugar in my system. 

airbull0424

A cheetah can run right around 60 miles an hour. So find one and right before you run him over, you are doing slighty more than 60 miles an hour. 



