Weigh-in-Motion:  Why are all those Trucks over in the Right Lane?

If you have traveled north on Interstate 5 from Olympia to Seattle, you have probably noticed two different areas where all of the trucks try to get over to the right lane — just before the scale houses at Nisqually and Federal Way.  You may have even seen the signs which say “Weigh In Motion: Trucks Use Right Lane Next 2 Miles.”  Here is the view about two miles south of the Nisqually scale:

If you think back to your driver’s education days, you know those white signs with black letters are referred to as a restrictive sign — they command a driver to do something.  So in this case, trucks are being ordered to get into the right lane.  In fact, they can be stopped by an officer if they are not in the right lane beyond these signs.  The driver must still move right in a safe manner, however — with proper signal and at a safe speed and distance from other vehicles. If you are in a passenger car, you should consider moving to the left two lanes and be aware of trucks trying to move over. 

For this particular scale, there are three sets of these signs reminding drivers to move right as they approach the Weigh in Motion (WIM) system. The entire system consists of sensors in the pavement as well as systems above ground which can sense vehicle heights and also read license plates and take photos of the trucks as they pass by so commercial vehicle enforcement officers can match up which vehicle is coming over the system with the weight being displayed on the computer inside the scale house.  The systems can also be monitored remotely. 

If you look at the photo above, you can see a few things: The pole contains the license plate readers and cameras and height sensing equipment.  If you look down at the roadway, you can see part of the weight system.  And bonus points if you also notice the truck which is definitely not in the right lane!

The WIM system helps officers focus on screening those trucks most likely to be overweight or have other safety violations — including those who may be operating in violation of an out-of-service order.  When it comes to overweight trucks, we know these impact of these trucks can not only damage infrastructure on our roadways but can also prove dangerous in decreased stopping distance and maneuverability. 

If a truck is screened in for further inspection, it is taken over the scales at the weigh station to verify and obtain a more precise weight.  Drivers face escalating penalties that correspond with the amount of exceeded weight. 

If you would like to learn more about the system, visit this page from our colleagues at the Washington State Department of Transportation (WSDOT).  If you are out traveling around our great state, keep an eye out for WIM at the following locations: