Geza Pesti

Guidelines for Spacing Between Freeway Ramps

Existing geometric design guidance related to interchange ramp spacing in the Texas Roadway Design Manual and AASHTOs Policy on Geometric Design of Highways and Streets is not speed dependent even though intuition indicates that spacing and speed are related. Understanding the relationship between interchange ramp spacing, speed, and freeway operations is important, especially in developing potential design values for higher speeds (e.g., 85 to 100 mph). The objectives of this Texas Department of Transportation project were (a) to investigate relationships between weaving length, speed, and overall vehicle operations for successive ramps on Texas freeways and (b) to propose updates to current guidance on recommended distances between ramps. Several methods were used to assist in developing guidance on ramp spacing lengths. The methods and resources used to generate potential lengths included (a) guidance provided in the Design Manual for Roads and Bridges published by the Highways Agency in England, (b) minimum deceleration and acceleration lengths for freeway conditions, (c) decision sight distance, (d) sign spacing needs, (e) NCHRP Project 3–75 findings, (f) findings from field studies at seven sites in Texas, (g) findings from simulation conducted as part of this research, and (h) safety relationships identified in the literature. Suggested ramp spacings were developed for the entrance–exit and exit–exit ramp scenarios.

Estimating Vehicular Emission Impact of Nighttime Construction with VISSIM and Different MOVES Emission Estimation Approaches

Shifting work zones from daytime to nighttime is a potential solution to air quality issues on roadway with high traffic volume and where it is undesirable to close lanes during peak hours. The expected benefit of such shifting is to reduce total fuel consumption and on-road vehicle emissions. However, the magnitude of emission reductions and air quality impacts has not been examined comprehensively at work zones. The study presented in this paper investigated the traffic-related emission impacts of work zones using an urban freeway case study. A VISSIM test bed combined with the Environmental Protection Agency’s MOVES emission model was used to estimate total emissions assuming daytime and nighttime lane-closure scenarios. Vehicle emissions were estimated using a link-based method and operating mode-based method. The results from both methods demonstrated that nighttime construction has a significant impact on both traffic speeds and vehicle emissions, primarily as a result of reductions in vehicle miles traveled. In addition, a horizontal comparison between the results from the two methods was made to assess the impact of different emission estimation approaches. The outcomes from the comparison highlight the potential importance of the operating mode-based approach for accurately estimate total traffic emission quantities when data or simulations are available.

Work Zone Impact Assessment Methods and Applications

Two work zone impact assessment methods were developed and their applicability was illustrated with data from recent construction projects on the I-35 Central Texas corridor. The first method was developed for postevent analyses of the impacts of freeway construction activities, incidents, and special events. The impacts were evaluated in terms of travel times and delay. An interval estimate for maximum queue length was also provided. Travel times and speeds were obtained by Bluetooth address matching. The method has also been used for determining work zone mobility performance measures, verifying the suitability of queue warning systems, and providing feedback for future deployment decisions. Based on more than 3 years’ experience with the analysis of impacts of road construction and maintenance projects as well as some major incidents on the I-35 corridor, the Bluetooth-based postevent closure analysis tool has proved to be very cost-effective. The second method was developed for determining the best closure schedule and start time for planned work zone lane closures. The best closure start time is the one that is expected to create the shortest queue lengths and has the least negative impact on travelers. The required input includes historical traffic volumes at a point upstream of the planned lane closure and estimated work zone capacity. The work zone capacity can vary over the duration of the work zone. The method runs input–output analysis in a dual-loop framework to analyze the impact of all available closure schedule scenarios and selects the best closure start time with the shortest expected queues.

Regional Impact of Roadway Construction on Traffic Operations

The objective of this study was to develop a methodology for assessing the impact of road construction that could be used to (a) predict the network-level impact of road construction projects, (b) identify critical roadway segments and corridors in which the impacts of construction are expected to be the most severe, and (c) compare alternative construction scenarios and schedules. Dynamic traffic assignment formed the basis of an approach to assess the regional impact of road construction and compare alternative construction schedule scenarios. The application of the model was illustrated with the use of a hypothetical case of two road construction projects in the roadway system of El Paso, Texas.