There are number of ways speed can be captured within the wide variety of fleet tracking systems available in today’s market…some good, some not so great. In our typical approach with transparency, we thought we would share how we do it. Happy reading!
1. GPS is used to calculate Speed and Distance –The unit is actually taking GPS readings 60 times a second and we use this to calculate both distance and speed. The quality of the GPS readings plays an important part in the calculations. If we have a good satellite count the data is more accurate. When you have a lower Satellite count you can actually get GPS readings that are “bad” (i.e. if we are getting GPS bounce off buildings or even certain roads in Mountainous areas can cause the “canyon” affect, which is simply false GPS readings due to the signal bouncing off things). So, when we get a reading that appears “false” we need to actually discard that particular data.
2. Mapping and Posted Speed Data – We use Google’s Mapping, Address Database and Posted Speed database in our system. The tracking unit actually records the location data in Latitude and Longitude. The location data (LAT/LON + date & time, + Speed + distance travelled) is sent into our servers (every 1 minute + turns of >20 degrees) by the tracking unit.
3. Location Data – Is converted to a Street Address by a reverse geocoder and stored in the system. It takes the LAT/LON and converts it to the Closest Address to that LAT/LON based on the google address database. The “closest address” depends on the property size and the spot on the property that the google address data base converts it to. So while accurate the vast majority of the time, certain properties could put our dot in a spot that’s different from the actual original LAT/LON reading. It’s actually something we can’t control.
4. Speed Data – We track Speed at each location reading (every 1 minute + turns) and we send in the MAX speed that occurred during that interval. We have two types of Speed alerts:
a) Max Speed Alert – The user can set a speed alert for a MAX speed. For example, MAX speed at 80 MPH. So as the speed data is analyzed, if the system sees a speed greater than 80 MPH, it will trigger an alert. This is truly only a MAX speed alert.
b) Posted Speed (also known as relative speed or Speed vs. Speed limit) – In the case of Posted Speed, the system is actually comparing the location of the speed reading to the actual Posted Speed limit in Googles Speed Limit database. While this would appear like a simple task, the challenge that all GPS providers face is the fact that the GPS readings are not exactly in the middle of the road and Posted Speed limit database information is not always 100% accurate (just imagine how many roads, how many school zones, curves, speed limit changes that happen throughout the country, it’s impossible to keep track of that perfectly).
5. Smart Speed Logic – This is sophisticated filtering that we designed, and it simply means, we verify a few readings before & a few readings after each speed reading we receive before we determine if it’s a Posted Speed Violation. We do these calculations on the server about every 10 minutes, so it’s essentially reviewing the speed data in clumps of data.
a) We are looking to make sure that we compare the speed readings and that there are at least 3 readings in a row on the same road with the same posted speed limit, before we consider it to be Posted Speed Alert. This ensures we don’t accidently report a speed alert from a side Street or from an underpass, tunnel etc., as we do not want to provide incorrect speed alerts.
b)Google does not have speed limits in their database for every inch of every highway. They use a default speed limit of 25KPH (16MPH) in their database and we have chosen to filter those out as well.
c) So, there will be cases where we show a speed on a location data view, yet there may not be a posted speed limit on that road.
d) Posted Speed Alerts are NOT instant alerts – since we are using the blocks of serval locations/speed data the alerts are generated in about 10-minute intervals.
Challenges with Posted Speed Alerts -There are times where the street addresses change, and since we are trying to reduce the false alerts (side streets, off ramps etc.) there will be times that we actually miss a posted speed alert as it’s impossible to create a logic that can anticipate a street name that changes and then changes back. Check out the image below, this customer had a Posted Speed limit set at + 15mph and you can see they clearly tried to trigger the speed alert. In this particular case, we missed the speed alert because the street names changed significantly. If you look at the two examples below, the roads clearly change names on the google address database. On the map, you can see it’s all the same road.
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