Traffic Speed Report No. 121

Narrow, rural two-lane highways are mostly characterized by low design features, light traffic volumes with high crash rates, and particularly high fatal crash rates. About 5,000 mi of these highways are administered by the Louisiana Department of Transportation and Development. Run-off-roadway (ROR) crashes are the most common type of crashes on narrow, rural two-lane highways. Because the Manual on Uniform Traffic Control Devices does not require edgelines, edgelines are not found on many such highways because of their low traffic volumes. There are two main concerns for edgeline implementation on narrow two-lane highways: the potential increase in head-on collisions and the added maintenance cost to the already constrained annual maintenance budget. The second part of a study that evaluated the safety impact of edgelines on narrow, rural two-lane highways in Louisiana is presented. On the basis of data collected from 10 locations, the first part of the study proved that edge lines centralized the lateral position of vehicles. This second part of the study evaluated the safety performance before and after the implementation of edgelines on roadway segments selected from all Louisiana districts. By using the empirical Bayes method, the study showed that edgeline implementation significantly reduced expected crash frequencies. Edgeline implementation reduced ROR crashes as well as head-on crashes. The implementation of edgelines benefited primarily male drivers and young drivers. Because of the crash-decreasing trend observed in the 3-year period classified as the after period in this study, the final estimated crash modification factor was 0.85 with a standard deviation of 0.039. The high benefit–cost ratio strongly supports edgeline implementation on narrow, rural two-lane highways in Louisiana.

This report is an analysis of spot speed observations made during the 1983 summer months of June, July and August. All observations were made of free-flowing vehicles on level, tangent sections of rural and urban highways under favorable conditions. All observations were made during daylight. This is the third report with exclusively summer observations since 1975. From 1976 until 1980 (Traffic Speed Reports Nos. 95 through 114) 14 primary and secondary stations as well as another 14 randomly selected stations were monitored every quarter in conjunction with the speed certification performed for the Federal Highway Administration. Since 1981 the state and federal studies have been conducted separately. Fourteen speed monitoring stations were used for the 1983 Traffic Speed Report calculations. These stations are divided into four categories which include: four rural interstate locations, four rural four-lane locations, four rural two-lane locations and two urban interstate locations. These 14 stations are the same as the primary and secondary control stations monitored since 1975 in Indiana. Prior to 1975 only the 12 rural stations were monitored. The locations of the 12 rural stations are essentially the same since 1970 except for stations 4L-32 (formerly number 6 on US 52) and 2L-54 (formerly number 11 on US 31), which changed in 1975. The speed limit at all the stations is 55 mph. The site locations are given in Table 1 and shown in Figure 1. The vehicles were classified as Indiana or Non-Indiana Passenger Cars and light (less than 5000 lbs. gross weight) or heavy (equal to or more than 5000 lbs. gross weight) trucks. Computer analysis was performed for each vehicle classification and for combined passenger cars and combined trucks.

Mixed logit model-based driver injury severity investigations in single- and multi-vehicle crashes on rural two-lane highways

This paper presents an empirical investigation into performance indicators on two-lane rural highways. Field data from four study sites in the state of Montana were used in this investigation. Six performance indicators were investigated: average travel speed, average travel speed of passenger cars, average travel speed as a percent of free-flow speed, average travel speed of passenger cars as a percent of free-flow speed of passenger cars, percent followers, and follower density. The study examined the level of association between the selected performance indicators and major platooning variables, namely, traffic flow in the direction of travel, opposing traffic flow, percent heavy vehicles, standard deviation of free-flow speeds, and percent no-passing zones. Among all platooning variables investigated, traffic flow in the direction of travel was found to have the highest correlation with performance indicators. Other platooning variables exhibited only weak correlations with performance indicators. Also, follower density followed by percent followers exhibited the highest correlations with platooning variables.

Rural Interstate Highways *RI-21 (1-69) First bridge south of junction with S.R. 18 [Had to move location due to construction. Location taken was 3.4 miles north of S.R. 18 and near 68 mile marker.] *RI-6

A coordinated effort is under way to develop a Highway Safety Manual (HSM) for use in making quantitative estimates of the safety performance of specific highway types and quantitative estimates of proposed improvements to specific highway types. The highway types being addressed in the first edition of HSM are rural two-lane highways, rural multilane highways, and urban and suburban arterials. Explicit consideration of pedestrian safety on urban and suburban arterials is considered critical to implementation of the first edition of HSM. The objective of the present research was to develop a methodology for quantifying the effects of existing site characteristics and proposed improvements on urban and suburban arterials on pedestrian safety. The pedestrian safety prediction methodology has been developed to function as a component of the overall safety prediction methodology for urban and suburban arterials proposed for the first edition of HSM. In the present research, a methodology for prediction of vehicle–pedestrian collisions at signalized intersections was developed. This methodology includes base models for three- and four-leg signalized intersections and several accident modification factors.

The effects of the new 65 mile-per-hour speed limit on rural highway fatalities: A state-by-state analysis

The objective of the research presented in this paper was to develop a volume warrant for free right-turn (FRT) lanes at unsignalized intersections on rural two-lane highways. The warrant was based on a cost-benefit analysis that determined the right-turn volumes required to justify the construction and maintenance of FRT lanes at such locations. The research involved the evaluation of the safety and operational effects of FRT lanes. The safety effects of FRT lanes were determined from a comparison of the accident experience at intersections with and without FRT lanes. The operational effects of FRT lanes were analyzed using kinematic and traffic flow models. FRT lanes were not found to affect the frequency, severity, or types of accidents that occur at unsignalized intersections on rural two-lane highways. Thus, the benefits of FRT lanes are limited to improving the efficiency of right-turn movements. The results of the research indicate that design-year right-turn annual average daily traffic ranging from 440 to 825 vehicles per day, depending on the percentage of trucks, is required to warrant an FRT lane. A design speed of 64 km/h (40 mph) was found to be the most cost-effective design speed for FRT lanes. However, design speeds up to 89 km/h (55 mph) do not significantly reduce the cost effectiveness of an FRT lane.

Calibration and development of safety performance functions for two-way stop-control intersections on rural two-lane highways in Louisiana

Passing Behavior on Rural Two-Lane Highways Ayman A. Abdul-Mawjoud Gandhi G. Sofia College of Engineering College of Engineering University of Mosul-Iraq University of Al-Mustansriya-Iraq Abstract Passing on rural two-lane highways is one of the most important driving tasks. More than 28000 vehicles were observed and the passing maneuvers were recorded of 10 two-lane highways in northern Iraq during June and July months of 2005. It was found that the number of passing maneuver increase as the flow rate for both directions increase up to 1500 veh/hr flow rate. The passing maneuvers decreases with the increase in flow rate. The increase in flow rate causes an increase in demand of passing and decrease in passing supply. Volume of around 212 veh/hr gives a balance between demand of passing and passing supply. Keywords: flow rate, passing maneuvers, rural highway, two-lane highway. الاجتياز في الطرق الخارجية ذات الممرين د. أيمن عبد الموجود د. غاندي صوفيا كلية الهندسة / جامعة الموصل كلية الهندسة الجامعة المستنصرية المستخلص تعتبر عملية الاجتياز في الطرق الخارجية ذات الممرين واحدة من اهم مهمات قيادة المركبات. تم ملاحظة اكثر من 00222 مركبة وتسجيل مناورات الاجتياز لعشرة طرق ذات الممرين في شمال العراق خلال شهري حزيران وتموز 0222 . تبين ان عدد مناورات الاجتياز يزداد والى معدل جريان 0222 مركبة/ساعة, مناورات الاجتياز تقل بزيادة معدل الجريان, الزيادة في معدل الجريان يسبب في زيادة على طلب الاجتياز ونقصان في تجهيز الاجتياز. ان الحجم المروري بحدود 000 مركبة/ساعة تعطي التوازن بين الطلب على الاجتياز وتجهيز الاجتياز. الكلمات الدالة: معدل الجريان, مناورة الاجتياز, الطرق الخارجية, الطرق ذات الممرين.

In the design consistency literature, the development of speed prediction models has concentrated on passenger cars, with little attention given to truck speed models. On some two-lane rural highways, however, trucks represent a large enough percentage of vehicles that they may be considered the design vehicle. The objective of the study was to develop operating speed prediction models for trucks on two-lane rural highways. A series of regression models was developed using a combination of field data and simulated data. First, the “Traffic on Rural Roads” and “Two-Lane with Passing” (TWOPAS) simulation models were critically assessed, and TWOPAS was selected to be used in further analysis. Next, field data from 17 sites were used to evaluate TWOPAS’s capability in the prediction of passenger car speeds and truck speeds. On the basis of the results of this evaluation, 13 sites were selected for use in simulating truck operating speeds. These sites were used to generate additional speed data for inclusion in the database for model development. Finally, a series of regression models was developed to predict 85th percentile truck operating speeds upstream, along, and downstream of a horizontal curve. These models consider the effect of length and grade of approach tangent, horizontal curve radius, and length and grade of departure tangent.

Predicting highway safety performance in quantitative terms on the basis of a set of highway geometric design and traffic control features is the core of the ongoing Highway Safety Manual (HSM) development. While great efforts have been made to develop safety performance models for different types of highways, evaluating the applicability of the models with crash data from states that were not used in the original model development is equally important. This step is critical in future HSM applications because of many noticeable differences in crash data recording practice and driving behaviors across the various states. Potential application concerns need to be evaluated fully and addressed before the manual is officially published. This paper presents the application experience of the safety prediction models and methodology for segments of two-lane rural roads as proposed for inclusion in Part III of the HSM. The study used data for state routes in Louisiana. The results indicate that the prediction models performed reasonably well: there were small differences between the observed and predicted crash frequencies, with calibration parameters applied, for all segments on rural two-lane highways in Louisiana. The results at different analysis levels (from individual segments to a network of segments) are summarized, and several application issues such as the level of effort versus degree of accuracy, simplification of the calibration process, and the need for a reliability measurement are discussed.

Predicting highway safety performance in quantitative terms on the basis of a set of highway geometric design and traffic control features is the core of the ongoing Highway Safety Manual (HSM) development. While great efforts have been made to develop safety performance models for different types of highways, evaluating the applicability of the models with crash data from states that were not used in the original model development is equally important. This step is critical in future HSM applications because of many noticeable differences in crash data recording practice and driving behaviors across the various states. Potential application concerns need to be evaluated fully and addressed before the manual is officially published. This paper presents the application experience of the safety prediction models and methodology for segments of two-lane rural roads as proposed for inclusion in Part III of the HSM. The study used data for state routes in Louisiana. The results indicate that the prediction models performed reasonably well: there were small differences between the observed and predicted crash frequencies, with calibration parameters applied, for all segments on rural two-lane highways in Louisiana. The results at different analysis levels (from individual segments to a network of segments) are summarized, and several application issues such as the level of effort versus degree of accuracy, simplification of the calibration process, and the need for a reliability measurement are discussed.

A Traffic Kinetic Model Considering Desired Speed

The Highway Capacity Manual prescribes level-of-service (LOS) criteria as a function of traffic density to categorize the operational conditions of both rural and urban freeway sections. This density-based level of service is ideally suited to the assessment of urban freeways when the performance must be optimized to meet high traffic demand. There is, however, some question as to whether density is the appropriate indicator of the quality of service on rural freeways, since drivers may think more in terms of psychological or emotional comfort for freeways, which generally serve long, high-speed trips and rarely experience more than moderate congestion levels. Three specific measures are examined that have at least an intuitive relationship to the concept of driver comfort: ( a) acceleration noise, which is a measure of the physical turbulence in the traffic stream; ( b) number and duration of cruise control applications, which could serve as a general indication of driver convenience or inconvenience; and ( c) percent time spent following, which is already accepted as the basis for determining the level of service on rural two-lane highways. The three candidate measures were estimated for a hypothetical section of rural freeway by simulation, using the CORSIM model. The kinematic relationships of individual vehicles within the traffic stream were estimated by postprocessing the simulation data for each second of operation. All of the measures considered in this study have conceptual appeal. All have produced interesting and potentially usable results with respect to their relationships to traffic volume. Although the simulation results are interesting, further studies focusing on driver opinions, behavior, or field measurements, or all three, would likely be necessary to support the development and recommendation of a specific set of LOS criteria that recognizes the differences between the urban and rural freeway driving environments.