The results of research involving a well-designed before-and-after evaluation of the safety effects of providing left- and right-turn lanes for at-grade intersections are presented. Geometric design, traffic control, traffic volume, and traffic accident data were gathered for a total of 280 improved intersections as well as 300 similar intersections that were not improved during the study period. The types of improvement projects evaluated included installation of added left-turn lanes, added right-turn lanes, and extension of the length of existing left- or right-turn lanes. An observational before-and-after evaluation of these projects was performed by using several alternative evaluation approaches. Three contrasting approaches to before-and-after evaluation were used: the yoked comparison or matched-pair approach, the comparison group approach, and the empirical Bayes approach. The research not only evaluated the safety effectiveness of left- and right-turn lane improvements but also compared the performances of these three alternative approaches in making such evaluations. The research developed quantitative safety effectiveness measures for installation design improvements involving added left-turn lanes and added right-turn lanes. The research concluded that the empirical Bayes method provides the most accurate and reliable results. Further use of this method is recommended.

This research investigates the relationship between lane width and safety for roadway segments and intersection approaches on urban and suburban arterials. The research found no general indication that the use of lanes narrower than 3.6 m (12 ft) on urban and suburban arterials increases crash frequencies. This finding suggests that geometric design policies should provide substantial flexibility for use of lane widths narrower than 3.6 m (12 ft). Inconsistent results were found which suggested increased crash frequencies with narrower lanes in three specific design situations. Narrower lanes should be used cautiously in these three specific situations unless local experience indicates otherwise.

An understanding of the relationship between lane width and traffic operations is important in making decisions about urban and suburban arterials. Numerous geometric elements, including lane width, affect the saturation flow rate at an intersection on an urban or suburban arterial. Several studies have been conducted to evaluate the relationship between lane width and saturation flow rate at intersections. This relationship is investigated on urban and suburban signalized intersection approaches by using field-study sites with the most ideal conditions possible. Research results indicate that saturation flow rate varies with lane width. Average saturation flow rate was in the range of 1,736 to 1,752 passenger cars (pc)/h/ln for 2.9-m (9.5-ft) lanes, 1,815 to 1,830 pc/h/ln for 3.3- to 3.6-m (11- to 12-ft) lanes, and 1,898 to 1,913 pc/h/ln for lane widths of 4.0 m (13 ft) or greater. These measured saturation flow rates are generally lower than those currently used in the Highway Capacity Manual (HCM). Furthermore, the percentage difference in saturation flow rate between sites with 2.9- and 3.6-m (9.5- and 12-ft) lanes was about half the value used in the HCM. Because data were limited to queue lengths between 8 and 11 vehicles, the research results do not directly address queue lengths longer than 11 vehicles.

Several methods, including one that supplements signage with beacons or embedded LEDs, have been used to emphasize the presence of a pedestrian crossing. A device that has received national attention is the rectangular rapid-flashing beacon (RRFB). A question that is being asked about the device is whether the beacons need to be rectangular. Could they be circular? For a comparison of the two devices, RRFBs and circular rapid-flashing beacons (CRFBs) were installed at 12 sites in four cities (i.e., Milwaukee, Wisconsin; Flagstaff, Arizona; Austin, Texas; and College Station, Texas). CRFBs were installed initially at half of the sites, while RRFBs were installed at the other half. The same flash pattern was used in all cases, regardless of beacon shape. A staged pedestrian protocol was used to collect driver yielding data to ensure that oncoming drivers received a consistent presentation of approaching pedestrians. The preliminary findings showed only minor, if any, differences between the CRFB and the RRFB (i.e., average daytime yielding rate with CRFB was 63%; it was 59% with RRFB). The results from the generalized linear mixed model indicated no significant differences between the two beacon shapes ( p-value = .4717). For a subset of the sites, the luminous intensity (also called brightness) of the beacons was measured. There was evidence of an increasing yielding rate with increasing intensity at night. In conclusion, the shape of the yellow rapid-flashing beacon did not have an impact on whether a driver decided to yield to waiting pedestrians.

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