Application of the Traffic Thermostat for the I-30 Managed Lanes in Dallas
Corresponding Author: Nick Wood, Texas A&M Transportation Institute
Presented By: Nick Wood, Texas A&M Transportation Institute
- Mark Burris, Texas A&M University
- Tina Geiselbrecht, Texas A&M Transportation Institute
- Natalie Bettger, North Central Texas Council of Governments
- Dan Lamers, North Central Texas Council of Governments
Managed lanes have historically experienced an evolution of change in operational policies. Over time, speeds on a managed lane may degrade due to oversubscribed demand. Operators have strategies they can use to mitigate problems and maintain optimal performance, including changing the occupancy requirement, varying tolls (if the facility is priced), and altering transit service. Assessing the potential impact of operational strategies is a challenge. The traffic thermostat tool is a software-based guide that helps select specific strategies projected to influence the metrics for each goal. This presentation outlines how the tool was adapted for use on the I 30 managed lanes in Dallas, Texas, a high-occupancy toll lane with reduced toll rates for qualifying carpools. An example scenario shows the consideration of travel speed and throughput goals, with acceptable performance thresholds of 50 mph and 5700 persons per hour (for the entire facility). The thermostat estimated values of projected speed and throughout for selected operational fixes using the calibrated speed-flow relationship from the regional travel demand model. Results from a quantitative travel survey helped to derive mode shift elasticities for use by the tool. Overall, the dynamic nature of demand, diversity of user groups, ambiguity with exogenous factors (e.g., regional unemployment, fuel prices), and need for extensive data on the lanes led to uncertainty and difficulty with prediction capability. However, using the traffic thermostat can show policymakers and others the inherent challenge of performance management for managed lane facilities.