Chunho Yeom

Field Investigation of Highway Sign Damage Rates and Inspector Accuracy

This study sought to create a simulation model to provide the North Carolina Department of Transportation (NCDOT) with recommendations to improve its sign inspection and replacement procedures. This research focuses on two key factors built into the model: (a) the rate at which signs are damaged beyond usefulness based on natural or man-made causes and (b) the accuracy rate of visual sign inspections based on retroreflectivity. The research team conducted nighttime rides with sign inspectors in 5 of 14 NCDOT divisions. During subsequent daytime rides, the team measured sign retroreflectivity to allow estimation of sign deterioration and inspector accuracy rates. Data were collected for white, yellow, red, and green signs and for sheeting Types I and III. About 2.3% of inspected signs (per year) were damaged to the point of needing replacement, and inspectors did not reject a large percentage of signs that had retroreflectivity values below the proposed minimum Federal Highway Administration standard.

Analysis of Traffic Sign Asset Management Scenarios

Minimum traffic sign retroreflectivity standards proposed for the Manual on Uniform Traffic Control Devices by the FHWA will present numerous management challenges to state and local departments of transportation (DOTs) responsible for traffic sign assets. These DOTs are looking at how to comply with the standard while minimizing sign maintenance costs. This paper presents an analysis of several traffic sign retroreflectivity maintenance methods using a sign asset management simulation based on inspection and sign data gathered in the field. The simulation evaluated 30 sign asset management scenarios in terms of annual maintenance cost per sign and percentage of traffic signs not compliant with the proposed FHWA standard. The simulation results found that, generally, higher costs for sign maintenance resulted in a lower percentage of noncompliant signs. However, for some scenarios using the visual nighttime inspection method, lower percentages of noncompliant signs were found even with relatively low maintenance costs per sign. Increasing the maintenance cost per sign by 10% resulted in an approximately 10% or more reduction in the number of noncompliant signs. It is recommended that DOTs implement a 100% Type III sign replacement policy because Type I signs have a greater life-cycle cost than do Type III signs. DOTs need to allocate an adequate annual budget for sign replacement and should establish their own minimum retroreflectivity standards. The sign asset management simulation developed as part of this study could be modified so that its use could be extended to other DOTs.

Innovative Work Zone Capacity Models from Nationwide Field and Archival Sources

Freeway work zone capacity has been the focus of significant research, but most studies were limited to specific geographic regions or work zone configurations or both. To date, no work zone predictive capacity model exists for U.S. freeways that is based on a geographically representative data set or sensitive to key geometric and operational attributes of the work zone. This paper proposes a new capacity model for freeway work zones, developed from nationwide field data fused with data obtained from an in-depth review of archived literature of prior work zone capacity studies in the United States. The proposed model estimates work zone capacity as a function of the lane closure severity index, barrier type, area type, lateral clearances, and daytime or nighttime work conditions. The model was successfully validated with 25% of the combined data that were not used for the model development. In addition, findings from literature archives suggested a 13.4% difference between prebreakdown, uninterrupted capacity and the ensuing queue discharge rate. The developed capacity model is intended to be incorporated into the next release of the Highway Capacity Manual and provides important insights on the relative effects of work zone configuration and other variables on the expected capacity of freeway work zones.

Lane Utilization at Two-Lane Arterial Approaches to Double Crossover Diamond Interchanges

Double crossover diamond (DCD) interchanges, also known as diverging diamond interchanges, are popular and promising alternative interchanges that are increasingly being implemented nationwide. One unique feature of a DCD interchange is that through movements on the arterial road have to cross each other twice to complete their movements, while enabling left-turn movements from the arterial to the freeway to proceed without stopping at the downstream intersection. Consequently, interchanges with heavy left-turn movements are good candidates for DCD implementation. This unique feature of a DCD interchange means that there is a need to research lane utilization at the upstream approach intersection of DCD interchanges, as the lane use could be unbalanced. This unbalanced lane utilization could have a significant effect on operations at the first crossover and the interchange as a whole. This study examined lane utilization factors provided in the Highway Capacity Manual 2010 (HCM) for conventional diamond interchanges and found that they are not generally applicable to DCD interchanges. The study then proposed a lane utilization model calibrated with field data obtained at three DCD sites. The new model fit observed conditions at the DCD sites better than previously developed HCM factors. The model was then validated with three additional DCD interchanges, and validation results confirmed that the new model adequately predicted DCD lane utilization. The authors recommend that DCD interchange designers and analysts use the new model where it is applicable but also that more research be conducted to find lane utilization factors for other DCD configurations.

Comparison of Analytical and Field-Estimated Lost Times at DDIs

AbstractDiverging diamond interchanges (DDIs) are one of most successful unconventional type of diamond interchanges in the United States. This paper examines additional lost time due to internal l...

Simulation Guidance for Calibration of Freeway Lane Closure Capacity

This study provides a methodology for calibrating freeway work zone capacity in a microsimulation environment and guidance for replicating field-observed freeway work zone capacity through simulation. From 81 field observations at 12 U.S. work zone sites, 90 work zone sites from literature archival sources, and a macroscopic capacity model developed in NCHRP Project 03-107, the authors show how to replicate field-observed or forecast capacity in the Vissim simulation tool under various scenarios of freeway work zone lane closure. With guidance from an in-depth literature review, key car-following and lane-changing parameters are proposed as a result of the calibration effort and extensive sensitivity tests of numerous combinations of parameter values. Lane configuration specific guidance is provided for two key car-following parameters in Vissim, cc1 and cc2. During the process of developing the guidance, every tested capacity scenario was verified by using a lane use volume balance that was obtained upstream of the lane closure point in order to replicate realistic freeway work zone conditions. The calibration methodology as well as default parameter guidance developed through this research are useful to practitioners who wish to model freeway work zone impacts accurately through microsimulation.