Impacts of Trucks on Arterials LOS and Work Zone Lane Closure Analysis
Contracting Agency: FDOT
Principal Investigator: Dr. Lily Elefteriadou
Co-Principle Investigator: Dr. Scott Washburn
This project seeks to addresstwo distinct, but related areas of need for the Florida Departmentof Transportation. The first area relates to the impact of truckson arterial operations and Level of Service (LOS), while the secondarea of interest is regarding work zone lane closure analysis. Thebackgrounds and proposed tasks on each of these two areas are givenin the following sections.
A. Impact of Trucks onArterial LOS
Freight traffic growth hascontributed significantly to the growth in vehicle-miles traveled (VMT)as truck traffic has increased at a rate faster than person travelVMT. Trucks also have a disproportionate impact on roadway capacity.Depending on the context, a large truck can consume the equivalentof several cars worth of roadway capacity due to the physical size,the acceleration and other performance characteristics.
This disproportionate growth intruck volume can be attributed to a number of factors including thedispersion of population and employment, the shift of many freightitems from rail and other modes to truck and the changes in theeconomy and business practices such as just-in-time deliveries ofinventory items that increase delivery frequencies.
The Highway Capacity Manual (HCM),the world’s leading source for highway capacity and level of service determinations, provides a constant passenger car equivalent (PCE) factor of 1.5 cars for each heavy vehicle on a freeway and 2.0 carsfor an arterial. A growing number of professionals question thevalidity of this overall number in relation to today’s changingtraffic environment. In stop-and-go traffic, large tractor trailershave a much slower start-up time than passenger cars.
There is a growing need toquantify the actual effects of trucks on our arterial system. Withmore of the state system being physically or financially constrainedeach year, solutions for effectively moving freight traffic areneeded. By being better able to account for the effects of truckson the arterial system, it will be easier for planners and engineersto designate alternate routes which provide better and more reliabletruck movement.
With increasing numbers oftrucks on our roadways, the impact of heavy vehicles has become amore significant factor on our level of service analysis.Essentially, we may be under-reporting the Level of Service (LOS)on facilities with significant truck volumes. This impactstransportation concurrency efforts. These related issues haverecently surfaced in District 7, Martin County, and Central OfficeDesign.
B. Freeway Work Zone Capacity
Chapter 10 of the FDOT PlansPreparation Manual (PPM) titled “Work Zone Traffic Control” containsa lane closure analysis procedure (pp. 10-30 – 10-43) thatcalculates the restricted capacity for roadway segments with a laneclosure. Based on the hourly traffic demand, restrictions may thenbe placed on the time of day/night that the lane can be closed.This procedure applies capacity reduction factors and other factorsto the capacity flow rate to determine the restricted capacity.
This procedure wasdeveloped approximately 10 years ago, and it is the desire of theDepartment to evaluate and update this procedure against morecurrent publications including the HCM2000 and available pertinentresearch. For this project, the evaluation should include therelevancy and accuracy of this application to freeways.
The Departmentintends to develop a decision matrix to assist engineers andcontractors in selecting the proper tools to evaluate laneclosures. It should be determined if more complex procedures and/ortools should be used under certain scenarios.