Tidbit Tuesday
Tuesday, November 12, 2019 at 3:14:17 PM
Tidbit Tuesday #6

It Ain't Heavy, It's My Trailer

Classifying heavy vehicles is an important part of data collection and analysis. Heavy vehicles affect everything from signal timing and pavement design to the size of roundabouts and intersections because their length, acceleration/decelerations rates and turning radiuses are different from typical vehicles. Accurately including vehicle classifications during counts could prevent future delay and design failures. When counting, remember that class 4 pickups and class 3 passenger cars pulling a trailer with 1 or 2 axles are still considered part of their respective class and not a heavy vehicle.

Understanding your analysis tool and how heavy vehicle classifications are considered is important, too. HCM analysis for an intersection combines classes 4 - 13 into one heavy vehicle percentage, but when using freeway analysis, you can separate it into Single-Unit Trucks and Tractor-Trailers. Microsimulation, on the other hand, allows you to categorize the vehicle classifications into whatever the analyst chooses to design. For analysis projects, DOTD recommends that vehicle classifications are separated into three (3) categories; Automobile classes 1-3, Bus/SU classes 4-7, and Truck classes 8-13.

For more detailed information on classifications and other topics, please see our TEPR website (http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Traffic_Engineering/Publications/Pages/TEPR.aspx).

If you'd like to contact us with any comments, questions or tidbits of your own, please email TrafficEngineering@la.gov. Thanks for reading!