Two-way Highways Research Articles

Daytime High-Speed Passing Maneuvers Observed on Rural Two-Lane, Two-Way Highway

Daytime high-speed passing maneuvers were recorded along a straight and flat 15-mi section of a rural two-lane, two-way highway in Texas. The posted speed limit was 70 mph. Passing maneuvers were covertly recorded from the overtaken vehicle, which was driven at three specific study speeds: 55, 60, and 65 mph. A total of 105 single-vehicle daytime passes were analyzed. Speed profiles of the passing vehicles’ passes were developed for each of the three studied speeds. The results were compared with AASHTO's assumptions and criteria for minimum passing sight distance (PSD) for two-lane, two-way highways. In particular, the analysis focused on the elements associated with a passing vehicle while it occupied the opposing lane of travel. The specific elements that were studied included these four: the average passing speed, the speed differential between passing and passed vehicles, the distance traveled while making the pass, and the total elapsed time. The general findings provided support for the AASHTO PSD model. For the assumptions made, the model provided reasonable results. However, the assumptions may need to be updated or to have more flexibility added. For instance, for a 70 mph design speed, the assumed speed of the overtaken vehicle is 54 mph in the AASHTO PSD model. The PSD associated with these speeds was verified in this study. But what if the overtaken vehicle was traveling at 60 or 65 mph? The results of this study show that the current AASHTO PSD model would provide inadequate PSD values for overtaken speeds greater than those currently assumed.

Evaluation of Operational Impacts of Installation of Centerline and Edge Line Rumble Strips

Research findings have shown that centerline rumble strips (CRSs) and shoulder rumble strips (SRSs) have significant safety benefits. SRSs have proved successful in reducing run-off-the-road crashes, and more recent research has shown that CRSs can potentially reduce head-on collisions. However, concerns about the operational effects of CRSs and SRSs remain. Specifically, how do the installations affect vehicle lateral position, passing operations, and shoulder usage? This paper documents the findings of research conducted for the Texas Department of Transportation on CRSs and edge line rumble strips (ERSs), a variation on SRSs that are placed directly on the marked edge line. Before-and-after analyses were conducted on Texas highways where CRSs or ERSs, or both, were installed. CRSs were evaluated with respect to passing operations and vehicle lateral position within the travel lanes; ERSs were evaluated for shoulder usage and vehicle lateral position during shoulder encroachments. The results of the study showed that CRSs generally improve vehicle lateral position by increasing the separation between opposing traffic streams on rural highways, although the results were mixed for curve sites. CRSs also have little effect on passing operations when they are installed in passing zones on rural two-lane two-way highways. ERSs were successful in reducing small, inadvertent encroachments onto the shoulder, whereas they had little impact on most normal shoulder usage.

Work Zone Lengths for a Four-Lane Road with an Alternate Route

Highway maintenance, like rehabilitation or resurfacing, on four-lane, two-way highways usually requires closing one or two lanes to set up a work zone. In this paper we evaluate several alternatives defined by the number of closed lanes, fractions of traffic diverted to alternate routes, and crossover of diverted traffic to opposite lanes. A methodology is developed to minimize the total cost, including agency cost, user cost, and accident cost, by optimizing work zone length for each alternative and finding optimal diversion fraction, while considering the characteristics of the detour route bypassing the work zone. Finally, guidelines for selecting the best alternative for different characteristics of traffic flows, roads, and maintenance processes are developed by deriving thresholds among alternatives.

Predicted 95th Percentile Speeds on Curved Alignments Approaching a Stop

The objective of this project was to develop a model that describes design speed profiles of vehicles traversing horizontal curves on approaches to stop-controlled intersections on two-lane two-way rural highways. Once speed prediction models were determined, a procedure for the design of horizontal curves that would accommodate vehicles transitioning from high speeds to a stop was developed. Speed profiles were developed with the use of data from 15 study sites in Nebraska. The multiplicative model was used to provide prediction equations for speed profiles. Separate profiles were created for passenger cars and heavy vehicles because speeds were significantly different. The heavy vehicle data were separated further for alignments with and without horizontal curvature. It was concluded that posted speed, median type, presence of rumble bars, roadway surface condition, and degree of rutting did not significantly affect the vehicle speed profiles at these sites at a 95% confidence level. During the comparison of speeds, it was found that the intercepts of the regression lines for approaches with and without horizontal curves were significantly different in the case of heavy vehicles. The speed of heavy vehicles on tangent approaches was generally about 8 mph higher than on sites that exhibited horizontal curvature. The rate of deceleration remained almost the same on all approaches to intersections, except near the stop. For passenger cars, there was no statistically significant difference between curved and tangent alignments. A guidebook for the geometric design of intersection realignment Methods A through D, referred to in the 2004 Green Book, is also included in the project's report.

Predicted 95th Percentile Speeds on Curved Alignments Approaching a Stop

The objective of this project was to develop a model that describes design speed profiles of vehicles traversing horizontal curves on approaches to stop-controlled intersections on two-lane two-way rural highways. Once speed prediction models were determined, a procedure for the design of horizontal curves that would accommodate vehicles transitioning from high speeds to a stop was developed. Speed profiles were developed with the use of data from 15 study sites in Nebraska. The multiplicative model was used to provide prediction equations for speed profiles. Separate profiles were created for passenger cars and heavy vehicles because speeds were significantly different. The heavy vehicle data were separated further for alignments with and without horizontal curvature. It was concluded that posted speed, median type, presence of rumble bars, roadway surface condition, and degree of rutting did not significantly affect the vehicle speed profiles at these sites at a 95% confidence level. During the comparis...

Work Zone Optimization for Two-Lane Highway Resurfacing Projects with an Alternate Route

Pavements on two-lane two-way highways are usually resurfaced by closing one lane at a time. Vehicles then travel in the remaining lane along the work zone, alternating directions within each control cycle. In an earlier work, Chen and Schonfeld developed a work zone optimization model for two-lane highways with time-dependent inflows and no detours, based on simulated annealing. In this paper, several alternatives are evaluated, defined by the number of closed lanes and fractions of traffic diverted to alternate routes. The algorithm referred to as SAUASD (simulated annealing for uniform alternatives with a single detour) is developed to find the best single alternative within a resurfacing project. The algorithm referred to as SAMASD (simulated annealing for mixed alternatives with a single detour) is developed to search through possible mixed alternatives and their diverted fractions, to minimize total cost, further including agency cost (resurfacing cost and idling cost) and user cost (user delay cost and accident cost). Thus, traffic management plans are developed with uniform or mixed alternatives within a two-lane highway resurfacing project.

Work Zone Optimization for Two-Lane Highway Resurfacing Projects with an Alternate Route

Pavements on two-lane two-way highways are usually resurfaced by closing one lane at a time. Vehicles then travel in the remaining lane along the work zone, alternating directions within each control cycle. In an earlier work, Chen and Schonfeld developed a work zone optimization model for two-lane highways with time-dependent inflows and no detours, based on simulated annealing. In this paper, several alternatives are evaluated, defined by the number of closed lanes and fractions of traffic diverted to alternate routes. The algorithm referred to as SAUASD (simulated annealing for uniform alternatives with a single detour) is developed to find the best single alternative within a resurfacing project. The algorithm referred to as SAMASD (simulated annealing for mixed alternatives with a single detour) is developed to search through possible mixed alternatives and their diverted fractions, to minimize total cost, further including agency cost (resurfacing cost and idling cost) and user cost (user delay cost and accident cost). Thus, traffic management plans are developed with uniform or mixed alternatives within a two-lane highway resurfacing project.

Work Zone Optimization for Two-Lane Highway Maintenance Projects

On two-lane, two-way highways, pavement resurfacing is usually done by closing one lane at a time. Then, vehicles travel in the remaining lane along the work zone, alternating directions within each control cycle. Such a work zone can be analyzed as a one-way traffic-control system in which queuing and delay processes are analogous to those at a two-phase signalized intersection. Efficient scheduling and traffic control through work zones may significantly reduce the total cost. A model is presented for optimizing work plans, including zone lengths, work durations, starting times, pausing times (if any), and control-cycle times, for work zones on two-lane highways. This is done by minimizing total cost, including agency cost (maintenance cost and idling cost) and user cost (user delay cost and accident cost), while taking into account traffic-demand variations over time. Two optimization methods, Powell's and simulated annealing, are adapted for this problem and compared. In numerical tests, the simulated annealing algorithm yields better solutions using less computer time than Powell's method.

Optimizing Work Zones for Two-Lane Highway Maintenance Projects

Highway maintenance is very expensive in terms of not only costs to the responsible agencies but also disruptive delays to users. Construction and maintenance activities on two-lane two-way highways often require the closure of one lane. During certain periods of a day, the user delay associated with lane closure may be quite intolerable to motorists. A numerical method is developed to optimize work-zone scheduling and traffic control on two-lane two-way highways where one lane at a time is closed. The objective is to minimize the total cost, including maintenance, labor/equipment idle, and user-delay costs, considering traffic flows varying over time. The optimized variables (e.g., work-zone lengths and cycle times) and the sensitivity results generated from a numerical example are presented in this study.

Determining the Best Method for Measuring No-Passing Zones

The objective of this study was to develop and test a suitable method for measuring passing sight distance on two-lane, two-way highways by using one person and vehicle. A literature review and contacts with state department of transportation (DOT) engineers revealed a number of current methods, and the research team developed several new methods. However, many of the current and new methods had problems that precluded agencies from using them. Five promising methods remained for an experiment testing their accuracy relative to the slow but trust-worthy walking method: the two-vehicle method, which is the most popular method used by state DOTs, a one-vehicle method used in a few divisions of the North Carolina DOT, a new laser rangefinder method, a new optical rangefinder method, and a new speed and distance method. The experiment provided data at 20 horizontal curve sites and 20 hill sites, equally split between the piedmont and mountain regions of North Carolina. The researchers recorded the time required to perform each method and also considered equipment costs, conservatism, and training needs. On the basis of these factors, the researchers recommend that highway agencies use the one-vehicle method to measure passing sight distance in most cases. The one-vehicle method was generally more accurate than the two-vehicle method, and it was superior to the new methods in several important ways.

Optimal Work Zone Lengths for Two-Lane Highways

Highway pavement maintenance is very expensive not only in terms of costs to the responsible agencies, but also in terms of disruptive delays to users. Construction and maintenance activities on two-lane, two-way highways often require the closure of one travel lane. Longer work zones and the longer cycle times associated with such zones tend to increase the user delay costs. Maintenance work can be performed more efficiently, i.e., with fewer repeated setups, in longer zones. A mathematical model is developed to optimize the work zone length and traffic control on two-lane, two-way highways where one lane at a time is closed. The objective is to minimize the total cost, including the agency cost and user delay cost. Unbalanced traffic flows in both directions are considered. The optimized variables (e.g., work zone length and cycle time) and the sensitivity results generated from a numerical example are presented in this study.