Passenger car equivalents (PCEs) have been used extensively in the Highway Capacity Manual to establish the impact of trucks, buses, and recreational vehicles on traffic operations. PCEs are currently being used for studying freeways, multilane highways, and two-lane highways. A heavy-vehicle factor is directly given for the impact of heavy vehicles at signalized intersections (and indirectly along arterials). These PCE values are typically based on a limited number of simulations and on older simulation models. In addition, the impact of variables such as traffic flow, truck percentage, truck type (i.e., length and weight/horsepower ratio), grade, and length of grade on PCEs has not been evaluated in depth for all facility types. The methodology for developing PCEs for different truck types for the full range of traffic conditions on freeways, two-lane highways, and arterials is described. Given the scope of this research and the variability of traffic conditions to be examined, simulation was selected a...

Development of Passenger Car Equivalents for Freeways, Two-Lane Highways, and Arterials

This study aims to propose a new algorithm to evaluate the rear-end collision risk under fog conditions considering reduced visibility. The proposed algorithm compares the safe stopping distance of the leading and following vehicles. According to the relationship between clearance distance between the two consecutive vehicles and visibility distance, the car-following maneuver is divided into different situations and the algorithms to calculate the safe stopping distances are suggested correspondingly. The visibility distance is collected by a new visibility detection system with adaptive learning modules and the clearance distance is obtained from a vehicle-based detector. By comparing the safe stopping distances of the following and leading vehicles, the potential rear-end collision can be identified. Subsequently, statistical tests are conducted to analyze rear-end collision risk and compare the different impact of reduced visibility on the collision risk for different vehicle types and lanes. Furthermore, random parameters logistic and negative binomial models are estimated by using individual vehicle data and aggregated traffic flow data, respectively, in order to explore the relationship between the potential rear-end crash and the reduced visibility together with other traffic parameters. The results suggest that the proposed algorithm works well in evaluating rear-end collision risk under fog conditions. It is found that reduced visibility has significant impact on the rear-end collision risk and the impact vary by the different vehicle types and by lane. Further, it is concluded that the driving maneuver of the leading and following vehicles can affect the rear-end collision risk. It is expected that the proposed algorithm can be implemented in a Traffic Management context to improve road safety under fog conditions. Specifically, it is suggested to implement the proposed algorithms in real-time and integrate it with ITS technologies such as Variable Speed Limit (VSL) and Dynamic Message Signs (DMS) to enhance traffic safety when the visibility declines. This car following algorithm could also be extended to adapt for the advent of Connected Vehicles in Fog conditions.

Developing an algorithm to assess the rear-end collision risk under fog conditions using real-time data

Gap-acceptance data are used to determine intersection sight distance, capacity, queue length, and delay at unsignalized intersections. They have also been used to determine the need for a traffic signal, the capacity of a left-turn lane, and warrants for left-turn signal phasing and storage lanes. A field study was performed to determine the gap-acceptance values of truck and passenger car drivers at six intersections. Each intersection was formed by two 2-lane roads; the minor road was controlled by a stop sign. The data obtained in the field were evaluated by three methods: Greenshield, Raff, and logit. The findings from the field studies were summarized into generalized values. Passenger car drivers had a 50% probability of accepting a gap of 6.5 sec for both left and right turns and an 85% probability of accepting a gap of 8.25 sec at a moderate- to high-volume intersection. A 10.5-sec gap represented the 85% probability of accepting a gap at an intersection where accepted gaps were influenced by low volume and the intersection's geometry. Truck drivers' 50% probability of accepting a gap was 8.5 sec. At a high-volume location, 85% of the truck drivers accepted a 10-sec gap; at a low-volume location, 15.0 sec was the accepted gap value.

Gaps accepted at stop-controlled intersections

The findings of a research project that was conducted to determine the amount of side friction demanded and provided for a range of roadway curvatures, vehicle speeds and types, and pavement surface conditions are described. Seven horizontal curves located on rural two-lane highways in Alberta as well as curves at the Calgary Police Service's Driver Training Facility were used as test sites. A three-axis accelerometer and a ball bank indicator were installed in seven test vehicles, including passenger cars, a half-ton pick-up, and a tandem-axle gravel truck. Lateral accelerations and ball bank readings were taken as the vehicles traversed test curves at constant speeds. Speeds were increased in increments of 10 km/hr until impending side skid conditions were reached. Ball bank readings are regressed upon lateral accelerations for each vehicle type, and equations predicting the implied value of safe side friction, the safe speed of the curve, and the margin of safety provided by the safe speed are developed. Maximum values of side friction demanded on dry and icy roadways are determined and used to calculate the margin of safety provided at various speeds. It was found that the current design standards are quite conservative and provide a more-than-sufficient margin of safety for motorists.

Side friction demanded and margins of safety on horizontal curves

The adequacy of the 1990 AASHTO geometric design policy for safely accommodating both passenger cars and trucks on horizontal curves is evaluated. The evaluation includes both the high-speed or open-highway horizontal curve design criteria in AASHTO Green Book Table III-6 and the low-speed design criteria for intersections and turning roadways in AASHTO Green Book Table III-17. The evaluation of current horizontal curve design policy is conducted by means of a sensitivity analysis that evaluates the margin of safety against vehicle skidding and rollover for both passenger cars and trucks traveling at the design speed on minimum-radius curves designed in accordance with AASHTO policy. It is concluded that current AASHTO horizontal curve design policy for rural highways and high-speed urban streets in Green Book Table III-6 provides an adequate margin of safety against both skidding and rollover as long as vehicles do not exceed the design speed of the curve. However under nearly worst-case conditions, skidding and rollover can occur on a horizontal curve, particularly at lower design speeds, if vehicles exceed the design speed by only a small amount. This finding suggests the importance of selecting a realistic horizontal curve design speed that will not be exceeded by substantial portions of the traffic stream. The AASHTO horizontal curve design criteria for intersections and turning roadways and low-speed urban streets, presented in Green Book Tables III-16 and III-17, are generally adequate for passenger cars that do not exceed the design speed, but may not be adequate for all trucks.

Horizontal curve design for passenger cars and trucks

Highway geometric design and traffic operations are based in part on consideration of vehicle characteristics. However, many of the current highway design and operational criteria are based on passenger car characteristics, even though truck characteristics may be more critical. This report reviews existing data for the truck characteristics that need to be considered in highway design, including truck dimensions, braking distance, driver eye height, acceleration capabilities, speed-maintenance capabilities on grades, turning radius and offtracking characteristics, suspension characteristics, and rollover threshold. The report also includes these truck characteristics. The highway design and operational criteria evaluated include sight distances, vertical curve length, intersection design, critical length of grade, lane width, horizontal curve design, vehicle change intervals at traffic signals, sign placement, and highway capacity. An assessment has been made of the need to change the current highway design and operational criteria to accommodate trucks. The cost effectiveness of proposed changes in design and operational criteria has been evaluated. This volume, Volume I, of the report presents the main findings of the study including recommended changes in highway geometric design and operational criteria to accommodate trucks. Volume II of the report contains appendixes documenting the detailed data collection and analysis activities.

Truck characteristics for use in highway design and operation. volume i: research report. final report

Highway geometric design and traffic operations are based in part on consideration of vehicle characteristics. However, many of the current highway design and operational criteria are based on passenger car characteristics, even though truck characteristics may be more critical. This report reviews existing data for the truck characteristics that need to be considered in highway design, including truck dimensions, braking distance, driver eye height, acceleration capabilities, speed-maintenance capabilities on grades, turning radius and offtracking characteristics, suspension characteristics, and rollover threshold. The report also includes these truck characteristics. The highway design and operational criteria evaluated include sight distances, vertical curve length, intersection design, critical length of grade, lane width, horizontal curve design, vehicle change intervals at traffic signals, sign placement, and highway capacity. An assessment has been made of the need to change the current highway design and operational criteria to accommodate trucks. The cost effectiveness of proposed changes in design and operational criteria has been evaluated (A).

Truck characteristics for use in highway design and operation; volumes 1 and 2

Highway geometric design and traffic operations are based in part on consideration of vehicle characteristics. However, many of the current highway design and operational criteria are based on passenger car characteristics, even though truck characteristics may be more critical. This report reviews existing data for the truck characteristics that need to be considered in highway design, including truck dimensions, braking distance, driver eye height, acceleration capabilities, speed-maintenance capabilities on grades, turning radius and offtracking characteristics, suspension characteristics, and rollover threshold. The report also includes these truck characteristics. The highway design and operational criteria evaluated include sight distances, vertical curve length, intersection design, critical length of grade, lane width, horizontal curve design, vehicle change intervals at traffic signals, sign placement, and highway capacity. An assessment has been made of the need to change the current highway design and operational criteria to accommodate trucks. The cost effectiveness of proposed changes in design and operational criteria has been evaluated. This volume, Volume II, of the report contains appendixes documenting the detailed data collection and analysis activities. Volume I of the report presents the main findings of the study including recommended changes in highway geometric design and operational criteria to accommodate trucks.

Truck characteristics for use in highway design and operation. volume ii: appendixes. final report

https://rosap.ntl.bts.gov/view/dot/933/dot_933_DS1.pdf

B T Kulakowski

Papers

Truck characteristics for use in highway design and operation. volume i: research report. final report

Truck characteristics for use in highway design and operation; volumes 1 and 2

Truck characteristics for use in highway design and operation. volume ii: appendixes. final report

Truck characteristics for use in highway design and operation. Volume II, Appendices