Marcus A Brewer

DESIGN FACTORS THAT AFFECT DRIVER SPEED ON SUBURBAN STREETS

Many roadway factors have an effect on driver behavior. Geometric, roadside, and traffic control device variables that may affect driver behavior on four-lane suburban arterials were investigated. Traffic signals and traffic volume were considered within the study site selection and data collection criteria and, therefore, were not included in the analysis. Regression techniques were used to determine how selected variables affect operating speed on horizontal curves and straight sections. When all variables were considered, posted speed limit was the most significant variable for both curves and straight sections. Other significant variables for curve sections were deflection angle and access density class. In another series of analyses performed without using posted speed limit, only lane width was a significant variable for straight sections, but median presence and roadside development were significant for curve sections. The analysis that included posted speed limit, however, produced stronger relationships between speed and significant variables than did the analysis that excluded posted speed limit.

Another Look at Pedestrian Walking Speed

Pedestrians have a wide range of needs and abilities. FHWAs Manual on Uniform Traffic Control Devices for Streets and Highways includes a walking speed of 4.0 ft/s (1.2 m/s) for calculating pedestrian clearance intervals for traffic signals. It also includes a comment that where pedestrians who walk slower than normal, or pedestrians who use wheelchairs, routinely use the crosswalk, a walking speed of less than 4.0 ft/s should be considered in determining the pedestrian clearance times. A 2005 TCRP-NCHRP study found a 15th percentile walking speed for young pedestrians of 3.77 ft/s (1.15 m/s) and a 15th percentile walking speed for older pedestrians of 3.03 ft/s (0.92 m/s). The study also determined that there is a statistical difference in walking speeds between older (older than 60 years) and younger (60 years and younger) pedestrians. Using population projections and the 15th percentile walking speeds for each population group more than 15 years old, the proportionally weighted 15th percentile walking...

Driver Yielding at Traffic Control Signals, Pedestrian Hybrid Beacons, and Rectangular Rapid-Flashing Beacons in Texas

This research effort explored the factors associated with higher driver yielding rates at pedestrian crossings with traffic control signal (TCS), pedestrian hybrid beacon (PHB), and rectangular rapid-flashing beacon (RRFB) treatments in Texas. The percentages of drivers yielding to a staged pedestrian were collected at 7 TCS sites, 22 RRFB sites, and 32 PHB sites. Overall, TCSs in Texas had the highest driver yielding rates, with an average of 98%. The average driver yielding rate for RRFBs in Texas was 86%, whereas the average for PHBs was 89%. The RRFB results for Texas were slightly higher than those found in other studies, perhaps because all RRFB sites included in this analysis had “School Crossing” signs and were located near a school. The number of devices within a city may have an impact on driver yielding. Those cities with a greater number of a particular device (i.e., Austin, Texas, for the PHBs and Garland, Texas, for the RRFBs) had higher driver yielding rates than cities where the device was used at only a few crossings. A comparison of the number of days since installation revealed statistically significantly higher driver yielding rates for those devices that had been installed longer. For PHBs, the results support the use of PHBs on roadways with multiple lanes or a wide crossing. For RRFBs, a lower rate of compliance was observed for longer crossing distances and indicated that for a certain crossing distance width, a device other than the RRFB should be considered.

Intermediate Access to Buffer-Separated Managed Lanes

A Texas Department of Transportation research project developed guidance on intermediate access to and from buffer-separated managed lanes located within general purpose lanes. For intermediate access openings, other communities recommend opening lengths between 1,300 ft and 2,000 ft (396 m to 610 m). While the recommended buffer width is 4 ft (1.2 m) or greater, many sites have a 2- to 3-ft (0.6- to 0.9-m) width. To assist in developing the guidance material, researchers recorded operations at five intermediate access sites. Characteristics measured included where the vehicle entered or left the managed lane (early, within one of two or three equal-distance zones, or late) and the lane of origin for the vehicle. A surprisingly large number of maneuvers (7%) was for vehicles passing a slower-moving vehicle. Approximately 9% of those moving into the high-occupancy vehicle (HOV) lane and 8% of those moving out of the HOV lane crossed the solid white markings (i.e., not in compliance with the pavement markings). The percentage of noncompliance increased to about 15% during those periods with low speeds [less than 40 mph (64 km/h)] or high speeds [greater than 60 mph (96 km/h)]. The percentage of maneuvers in compliance with the pavement markings varied by the length of the intermediate access opening. The compliance rate was greater for the longer access opening length [1,500 ft (457 m)] than for the shorter access opening length [1,160 ft (354 m)].

Safety Effectiveness of Super 2 Highways in Texas

The objective of this study was to evaluate the safety effectiveness of Super 2 highways in Texas. A before–after study was performed with the empirical Bayes (EB) method, which was superior to other methods because it could address the regression-to-the-mean bias. On the basis of potential study sites identified in seven districts (Paris, Childress, Corpus Christi, Austin, Wichita Falls, Yoakum, and Bryan) in Texas, four reference groups were considered by imposition of different restrictions. Negative binomial regression models were then used to develop safety performance functions for each reference group. From the model selection process, the most restricted reference group was selected for the final analysis. For roadway inventory and crash history data, 12 years (1997 to 2001 and 2003 to 2009) of data for Texas were examined. The analysis used fatal (K), incapacitating injury (A), nonincapacitating injury (B), and minor injury (C) crashes. Property-damage-only crashes were not included. The EB analyses were carried out on five corridors with about 53 centerline miles. The results showed that the installation of Super 2 highways led to statistically significant reductions in the incidence of crashes of 35% for crashes on segments only (KABC) and 42% for crashes on segments and at intersections (KABC) on the study corridors. These findings were consistent with those of previous studies of the safety of Super 2 corridors that showed improvements in safety with installation of passing lanes, even when traffic volumes were higher than those considered under previous guidance in Texas.

Super 2 highways in Texas: operational and safety characteristics

As traffic volumes increase in both urban and rural areas, so do demands on the highway network. Specifically, as rural traffic volumes rise in Texas, the pressure on the states network of two-lane highways rises accordingly. Previous research in Texas demonstrated that periodic passing lanes can improve operations on two-lane highways with average daily traffic lower than 5,000 vehicles. These highways, called Super 2 highways, can provide many of the benefits of a four-lane alignment at a lower cost. A recent project expanded on that research to develop design guidelines for passing lanes on two-lane highways with higher volumes. Researchers investigated the effects of volume, terrain, and heavy vehicles on traffic flow and safety. This paper discusses findings from field observations and crash analysis of existing Super 2 highway corridors in Texas and computer modeling of traffic conditions on a simulated Super 2 corridor. Results indicate that passing lanes provide added benefit at higher traffic volumes by reducing crashes, delay, and percent time spent following. Empirical Bayes analysis of crash data reveals a 35% reduction in expected nonintersection crashes with injuries. Simulation results indicate that most passing activity takes place within the first mile of the passing lane, so additional passing lanes can offer greater benefit than longer passing lanes. Whether new passing lanes are added or existing lanes are lengthened, the incremental benefit diminishes as additional length is provided and the highway more closely resembles a four-lane alignment.

Operational Characteristics of Super 2 Highways in Texas

As traffic volumes increase in many jurisdictions in both urban and rural areas, the demand on the highway network also increases. Specifically, as rural traffic volumes rise in Texas, the pressure on the states network of two-lane highways rises accordingly. High proportions of heavy vehicles compound the problem and contribute to a decrease in safety as impatient drivers attempt to pass slower vehicles in no-passing zones or to pass trucks, despite diminished sight distance beyond such vehicles. Previous research in Texas demonstrated that periodic passing lanes can improve operations on two-lane highways with low to moderate volumes; these Super 2 highways can provide many benefits of a four-lane alignment at lower cost. The current Texas Roadway Design Manual contains these guidelines for highways with average daily traffic (ADT) lower than 5,000 vehicles per day. A current project expands on that research to develop design guidelines for passing lanes on two-lane highways with higher volumes. The project investigates the effects of volume, terrain, and heavy vehicles on traffic flow. This paper discusses findings from field observations of existing Super 2 highway corridors in Texas and computer modeling of traffic conditions on a simulated Super 2 corridor. Results indicate that passing lanes do provide added benefit at higher traffic volumes by reducing delay and percent time spent following. The incremental benefit of adding passing lanes or adding length to lanes diminished, and the effects of ADT on operations were more substantial than the effects of terrain or truck percentage for the study corridor.

Traffic Enforcement Strategies for Work Zones

This report presents guidance for the safe and effective deployment of traffic enforcement strategies in work zones on high-speed highways (those with speed limits of 45 mph or greater). The planning, design, and operation of traffic enforcement strategies are discussed, as well as administrative issues that should be addressed. The report will be useful to traffic and construction engineers engaged in these types of projects.

Design Guidance for Freeway Main-Line Ramp Terminals

This paper presents the results of a study to develop improved design guidance for freeway main-line ramp terminals on the basis of modern driver behavior and vehicle performance capabilities. The primary steps included a crash analysis, an observational field study, and a driver behavioral study. This research reached several key conclusions, as follows. Vehicle merging speeds tend to be closer to freeway speeds at tapered acceleration lanes than at parallel acceleration lanes. The recommended minimum lengths for acceleration lanes presented in the 2004 edition of AASHTOs A Policy on Geometric Design of Highways and Streets (Green Book) are conservative and, under certain conditions, could be reduced by 15%. In a situation in which a significant volume of trucks uses an entrance ramp, an acceleration lane length that will better accommodate trucks can be derived by using speed–distance curves developed for a range of weight-to-power ratios. The recommended minimum lengths for deceleration lanes presented in the 2004 Green Book are conservative and do not account for deceleration in the freeway. Providing deceleration lanes longer than the minimum values given in the Green Book may promote casual deceleration by exiting drivers. Several potential changes for consideration in the next edition of the Green Book are recommended on the basis of the findings and conclusions of this research.

Design Guidance for Freeway Mainline Ramp Terminals

This report presents design guidance for freeway mainline ramp terminals based on current driver and vehicle behavior. The report will be useful to freeway designers and those responsible for developing design standards for freeway ramps. Special attention was given to the behavior of tractor-trailers and the report includes several speed-distance curves for tractor-trailers on grades up to 9% that could be useful in other applications (e.g., climbing lanes).