Updated March 21, 2019
There is a known issue in GPS-enabled devices, including those GPS units installed in traffic signal cabinets to provide time-based coordination, that may cause the GPS receivers to malfunction. This could have already happened without you realizing it or could begin happening on or after April 6, 2019. The issue is caused by the technology used to calculate the date. Here’s what it means and what you can do about it.
Traffic signal controllers that utilize external GPS receivers to set and maintain accurate date and time, may malfunction by resetting the date by up to 19.7 years. As an example, if a rollover took effect at 12:00:00 AM on Sunday, August 12, 2018 it would reset the controller’s date and time to 12:00:00 AM on Sunday, December 27, 1998. Note that the time-of-day and day-of-week are the same.
Many DOTs, County and City agencies rely on GPS units to maintain accurate time in their traffic signal controllers when utility or powerline frequencies drift from their 60 Hz cycle. In other instances, transportation agencies utilize GPS units to synchronize traffic controllers to a common time-base to promote the smooth flow of traffic. The GPS Week Rollover can hamper these coordinated corridors by resetting the day-of-week schedule where holiday timing plans may be in place.
For instance, the first holiday after August 12, 2018 was Labor Day, Monday September 3 (22 days later) where a holiday timing plan would have been in place. In the instance of the rollover, 22 days after December 27, 1998 is Monday, January 18, 1999 – a non-holiday where a holiday timing plan should not be in place. This could potentially create traffic backup for agencies who use holiday schedules in their signal timing plans.
Since not all chips were manufacturered on that same date, it is difficult to predict the exact date the rollover will take effect. After conferring with the chip manufacturers utilized in McCain's GPS modules, this is what we know thus far.
|Chip Manufacturer||Predicted Rollover Date|
We have every reason to believe that McCain units purchased within the last year are only one year into their 19.7-year lifecycle. The longer ago a unit was purchased, the more difficult it is to ascertain with a high-level of certainty, when the chip will reset. Accordingly, McCain recommends replacing any units purchased over 7-10 years ago.
There are no known fixes to universally update the GPS chips used in GPS Time Source Modules in part because the chips could be from one of many suppliers – namely Delorme, Trimble, or even from some suppliers that cannot be updated, like Furuno.
For obsolete or discontinued GPS modules, there is likely no choice but to upgrade the unit. For current GPS units, solutions include updating the existing GPS chip, disabling the date function via your local control software, or replacing the unit.
Trade-in your outdated GPS modules, regardless of who manufactured the original unit, and receive a 20% discount off the purchase of any new McCain GPS Modules.
Send us your McCain GPS units and we will attempt to upgrade the chip for you. Please note that not all units are repairable, such as those with Furuno GPS chips or obsolete plug-ins for 170 controllers.
To place your order, simply contact us and mention this offer. Offer valid for orders placed on or before September 30, 2019.
To help decide which solution is ideal for you, we recommend making a list of currently deployed units with their respective locations, and ranking them in order of priority. Priority should be based on the impact to your agency pending a GPS rollover, especially as it relates to your traffic coordination.
GPS modules from all traffic equipment vendors are at risk of being impacted by the GPS Week Rollover, including the following McCain GPS modules:
As a reminder, we have every reason to believe that GPS units purchased within the last few years, are only at the beginning of their lifespan. Issues will likely be more prevalent in units acquired in 2008 or earlier. However, we do not recommend updating units more than 7-10 years old; as it would be more cost effective to replace the units.
As we hear from other users and information develops on potential solutions, we will continue to bring you the latest information available.
If you have any information on methods you have identified, or if you have been able to resolve the issue, please share it with us.
The Global Positioning System (GPS) provides accurate timing information to many critical systems including the power grid, communications, financial markets, emergency services, and industrial controls. GPS-enabled receivers get date and time with accuracy to the second.
The methods used to develop this technology rely on a 10-bit transistor chip which allows binary numbers to range from zero (namely binary 0000000000) to 1,023 (binary 1111111111) for a total of 1,024 different combinations. This range of binary digits are then translated into working weeks in GPS systems, thus the GPS unit can distinguish 1,024 total weeks (19.7 years) within its range of 10 binary digits.
The first GPS units were deployed on January 6, 1980. For those units, the 1,024-week counter ran out and rolled over on August 21, 1999 at which time it reset to zero. Those units, which have been recounting since, will again reset on April 6, 2019.
While this recurring rollover issue is in effect, there are currently some chip manufacturers looking to increase the number of bits on the GPS chips to 13 binary digits. Though there are no chip manufactures that presently produce this chip-set, the transition to 13-bit technology would increase the timeframe between GPS resets to 8,192 weeks or nearly 158 years.