Speed Management Seems Simple

On the surface speed management seems almost like a silly topic. However, lawyers have won and lost cases based on speed. Police used radar guns to determine speed for many years and then introduced laser speed detectors because speed was not always correct. The definition for speed is “rate of motion” but what determines the “rate” varies. What also varies, is how fleet managers use the data to run their business. 

Calculating Speed

When you look into the mechanics of calculating speed all of the sudden your confidence wanes. Since a few MPH can make a difference when getting a ticket, violating company policy or acting in an unsafe manner, knowing an exact speed is important. 

In the “old days” speed was calculated using a mechanical process that could wear out. Many readers are old enough to have heard about a speed cable breaking when they were kids. Today, the cable has been replaced by a sensor. The general explanation of measuring speed and distance is to count the revolutions of a magnet mounted on the drive shaft or rotating component. The magnet passes a sensor and the time between rotations determines speed. The number of rotations determines distance. 

Speed Variables

The use of magnets and sensors eliminated the wearing of the old style cable making the speed more accurate. What has not changed is the rate of rotation is determine at a fixed wheel or tire size. In many vehicles, tires start with up to one inch of tread depth. From the day the vehicle moves, the speed is slowing getting inaccurate. To make things worse, tires that are not inflated to the exact amount used by the OEM will change the circumference of the tire as well. So treat wear and tire pressure but have a large combined impact on speed accuracy. 

Electronic-speedometer diagram

Electronic Speedometer

“Small magnets attached to the car’s rotating drive shaft sweep past tiny magnetic sensors (either reed switches or Hall-effect sensors) positioned nearby. Each time the magnets pass the sensors, they generate a brief pulse of electric current. An electronic circuit counts how quickly the pulses arrive and converts this into a speed, displayed electronically on an LCD display. Since the circuit is measuring the number of wheel rotations, it can also keep a count of how far you’ve traveled, doubling-up as an odometer (distance-measuring meter).”

by Chris Woodford, May, 23, 2021

GPS Speed

In modern times, technology has advanced with the introduction of GPS tracking using satellites. GPS tracking measures the time and distance between points on the ground and calculates the speed required to move from point A to point B. The benefit of GPS tracking speed management is the lack of moving parts which can wear out such as tires, cables and tire pressure. 

So Why Not Use GPS Speed Only?

GPS speed is used in some situations like heavy equipment. Speed management has to look at factors such as vehicle type, function, location, road conditions, weather, environment, and more. Controlling the speed of heavy trucks on a mining road keeps the road in a condition that allows trucks to travel at a known speed. A set speed is needed to coordinate the entire dance between vehicles transporting ore, the loading process and feeding the plant. If trucks cannot travel at a predictable rate, timing gets off. 

GPS speed is generally more accurate than the OEM speedometer the older a vehicle is. GPS speed is not without flaws. GPS speed is dependent on getting a signal from the satellites. If reception is blocked, speed calculations can be very far off, like by over 100 MPH. The anomalies are generally obvious but they can skew data if not filtered. 

Which Is More Accurate?

Generally speaking, GPS speed is more accurate when there are no mitigating circumstances like loss of signal from the GPS satellites. Tire pressure and wear are just to common to enable the OEM speedometer to be consistently accurate. One easy way to compare the two is to monitor speed on a smart phone to that on the dashboard. You will often times see a 3 MPH difference between the two. When pushing the envelope on the highway at staying 10 MPH below the speed limit, you may actually be over when you get measured with police radar. 

The historic challenge has been getting fleet operators and drivers to understand and accept the difference. In the GPS tracking and telematics industry this caused such an issue that most GPS tracking companies simply gave up and report the OEM speed. The difference in the data caused too many questions and long conversations; it was simply easier to go with what the customer was able to understand. 

Speed Management Consistency

Since speed can be measured several ways, which do you use when you have 300 vehicles and assets, from five different OEMs, and you are trying to standardize data? To do this on your own would be very expensive since data coming from OEMs varies even more.  Geotab has done the heavy lifting for you. The GO device can be used on any vehicle and this uses a single common method for collecting and reporting data. By installing a Geotab GO GPS device, fleets instantly have standardized data. In situations where OEM data is to be used, Geotab does some standardization when importing data through APIs but it is not at the same level or quality of plugging in a GO device. 

“To avoid data issues and variances, install a Geotab GO device, and avoid the OEM service differences.”

GPS Tracking & Dashcams

One method for improving speed management is to combine dashcams with GPS tracking and telematics. Dashcams bring a visualization to the circumstances in which speed is an important variable. Dashcams can help answer questions such as “Was a vehicle driving to fast for the weather conditions?” “Did the driver accelerate to run the yellow light?” With dashcam video information, fleet managers can better evaluate a situation to determine the best course of action. 

Although fleet dashcams are an optional expense, many insurance companies are requiring them to combat false accident claims and improve driver safe driving habits.

A single accident liability claim in the lifetime of a business can be more expensive than dashcams.