Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 122


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 121
121 PART 4 Detailed Two-Lane Roundabout: Golden, CO RCW Introduction a fairly gentle transition for vehicular traffic, but was selected to mitigate concerns on the impacts on traffic flow. It is This section describes analysis results of data collected at the expected that a higher elevation and/or steeper transition RCW of the two-lane roundabout in Golden at the inter- slope would drastically alter driver behavior, and these results section of Golden Road and Johnson Road (Exhibit 30). The therefore cannot be transferred directly to raised crosswalks analysis focus will be on pedestrian-related measures, includ- with different geometries. ing the availability and utilization of yield and gaps, as well as The raised crosswalk was further installed as a temporary pedestrian delay and O&M interventions. The measures are installation, and therefore no reconstruction was done to the defined in the methodology chapter of this report. curb line. Due to drainage considerations, the raised cross- Because of the two-lane approaches at this site, the section walk was at road surface level on the side of the street and distinguishes between near-lane and far-lane effects at the then sloped upward from there. For pedestrians this resulted crosswalk. These describe the vehicle state in the near and far in a somewhat uncomfortable walking experience since the lane relative to the position of the waiting pedestrian. crosswalk curb ramp down slope was followed by an up slope This section focuses on the south crosswalk with the treat- onto the raised crosswalk. For a permanent installation, it is ment effect of the raised crosswalk. The analysis presents recommended that drainage considerations be incorporated findings in the pre and post conditions for the studied cross- into a raised crosswalk design that is flush with the sidewalk. walk sequentially. The pre study was completed in July 2008, and a total of Pretest Pedestrian Behavior 18 blind travelers participated in the pre study. The treatment at the RCW was installed following the pre study, and 12 of the original 18 participants returned for the post experiment in Septem- The NCHRP Project 3-78A analysis of single-lane cross- ber 2008. ings used a performance evaluation framework that described the availability of crossing opportunities, the rate of utiliza- tion of these opportunities, as well as the delay and risk asso- Raised Crosswalk Evaluation ciated with the crossings. For a single lane, the yield and gap Raised Crosswalk Treatment Overview events are uniquely defined by the vehicle state in the conflict lane. However, at a two-lane crossing the analysis needs to An RCW (Exhibit 31) was installed at the southern leg of the consider the vehicle state in both lanes. The following analy- roundabout. The treatment had the objective of slowing driv- sis distinguishes between driver behavior in the near lane (the ers as they traversed the crosswalk, and the research team lane closest relative to the position of the pedestrian) and the hypothesized that the speed impediment may also result in an far lane. Depending on the crossing location (entry/exit and increased likelihood of drivers yielding. Overall, the raised curb/island) the near lane can be the inside or outside lane of crosswalk was a lower-cost treatment than the PHB but also the two-lane approach. The analysis defines the vehicle state affected drivers in the absence of pedestrians (the PHB rested in the near lane in five event categories: in "Dark" mode). The raised crosswalk was constructed from asphalt at a ver- 1. Rolling Yield (RY): Pedestrian encounters a driver who tical elevation of 3 in. and a 1:15 slope transition from the has slowed down for the pedestrian, but has not come to a existing pavement surface. This elevation and slope resulted in full stop.

OCR for page 121
122 Exhibit 30. Aerial view of roundabout. Exhibit 31. Raised crosswalk. Photo by Bastian Schroeder Photo by Google yield, stopped yield, crossable gap, non-crossable gap, and multiple events. The last category indicates that more than one event took place in the far lane during one near-lane event. For example, several cars could have gone through the far lane during one large gap in the near lane. For multiple events, the last event in the sequence is considered for 2. Stopped Yield (STY): Pedestrian encounters a driver who analysis. Exhibit 32 shows the near-lane and far-lane effects has come to a stop, defined as moving at a speed less than for the pre condition at the RCW. The event outcomes are 3 mph. broken down by whether the events were utilized by the 3. Forced Yield (FY): Pedestrian initiates crossing before the pedestrians. vehicle initiated the yield, but then forces the driver to The exhibit shows that 183 of 686 encountered events in the slow down by entering the crosswalk. near lane (26.7%) were yields, but that only some of those 4. Crossable Gap (CG): Pedestrian encounters a gap large events were associated with a yield or crossing opportunity in enough to safely cross the street. A crossable gap is defined the far lane. Participants did not utilize 43 rolling yields and as the crossing width divided by 3.5 ft/s walking speed plus 40 stopped yields. The corresponding overall rate of yield uti- 2 s for start time and safety buffer. lization is 45.4%, but 16.4% of utilized yields in the near lane 5. Non-Crossable Gap (non-CG): Pedestrian encounters were forced by the pedestrian seizing the crosswalk. The analy- a gap between vehicles shorter than the crossable gap sis of the far-lane event shows that a majority of the non-utilized threshold. yields were attributable to either non-crossable gaps or multi- ple events in the far lane. Overall, 53.5% of yields were double The vehicle state in the far lane will be defined relative to yields with stopping or stopped cars in both lanes (including the near-lane condition in five principal categories: rolling forced yields), of which 61.2% were utilized. Exhibit 32. Nearfar lane effects, pre condition, for RCW. Far-Lane Event Near-Lane Lane Rolling Stopped Forced X-Able Non-X. Multiple Events Event Outcome Yield Yield Yield Gap Gap RY STY CG FY non-CG Total Rolling Yield Utilized 3 2 1 2 0 1 0 1 0 0 10 Non-Utlz. 3 8 0 0 28 1 1 1 0 1 43 Stopped Yield Utilized 7 22 9 17 1 2 0 2 0 0 60 Non-Utlz. 1 14 0 1 18 0 3 1 0 2 40 Forced Yield Utilized 2 6 3 12 2 1 0 3 1 0 30 Non-Utlz. 0 0 0 0 0 0 0 0 0 0 0 Crossable Gap Utilized 5 12 31 74 1 0 1 12 2 0 138 Non-Utlz. 1 2 0 3 21 0 0 1 0 9 37 Non-Cross. Gap Utilized 1 0 0 2 2 0 0 0 0 0 5 Non-Utlz. 8 7 0 15 266 2 0 3 0 22 323 Total 31 73 44 126 339 7 5 24 3 34 686