Studies: I-81/I-581 Auxiliary Lane Transportation Study

Cost and schedule ►

The Interstate 81 (I-81)/Interstate 581 (I-581) corridor experiences significant congestion due to high traffic volumes, including high-truck volume along northbound (NB) I-81 from Exit 141 to Exit 143. The study area included an approximately 1.5-mile long segment along I-81 northbound from Exit 141 to Exit 143. Only I-81 northbound was analyzed in this study. The study sought to develop preliminary design plans and detailed costs for auxiliary lanes along northbound Interstate 81 connecting Exit 141 and Exit 143.

A safety analysis was conducted by first using historical data to identify crash “hot spots” and focusing particularly on the identified high-crash density locations. Based on the findings, appropriate recommendations were made for improving geometric deficiencies identified within the study corridor.

Traffic operational characteristics were identified by analyzing roadway capacity and traffic operations for the freeway mainline and merge/diverge areas within the study corridor. Highway Capacity Software (HCS) was used to assess freeway and ramp operations and to develop operating travel speeds along the study corridor. This software provides a macroscopic view of traffic operations. In recognizing the limitations of HCS procedures in oversaturated highway systems in urban areas, additional analyses were performed using CORSIM software. This software provides a microscopic level of traffic operations.

The preliminary design plans, along with the traffic and safety analysis, developed for this study were used by the Roanoke Valley Transportation Planning Organization (RVTPO) to apply for funding to construct the auxiliary lanes through the House Bill 2 (now called SMART SCALE) funding program. In the following funding cycle, the RVTPO applied for and received funding the a parallel project to construct auxiliary lanes in the southbound direction. These two projects are being delivered together. For information on this project, please visit Interstate 81 Northbound and Southbound Auxiliary Lanes - Roanoke County.

Study: I-81/I-581 Auxiliary Lane Transportation Study


The proposed improvement project, to extend the auxiliary lane between Exit 141 and Exit 143, will provide a near-term mitigation to alleviate traffic congestion and improve safety in the study limits until a major improvement is defined, funded and constructed.

Major Milestones 

The study was completed in July 2016. 


Contact Info:

Michael Gray
(540) 494-8288

Lat/Long: 37.334572, -80.016767

Locality: Roanoke

Page last modified: March 25, 2023