Click for next page ( 18

The National Academies of Sciences, Engineering, and Medicine
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 17
17 BBS operations were implemented in June 2005 along a the maintenance staging and snow storage concerns. Loss of 0.9 mi extension of the Northwest Motorway between Great intended shoulder functions has not proven to be a problem at North Road and Rosebank Road. The shoulder improve- established BBS sites. ments cost approximately $1 million. The BBS projects in Auckland generally require buses to Traffic Safety merge into general traffic at interchanges. The BBS lanes generally start at the off "nose" and end before the off-ramp The most common concerns that were raised by survey re- gore point. Buses use the BBS through the on-ramp merge spondents dealt with traffic safety. Eleven types of traffic area. This practice has reportedly worked well, because the safety concerns were identified. buses are all large (visible) and on-ramp traffic is aware that the buses will not be competing for space in the general traf- Conflicts at on- and off-ramps; fic lanes once past the interchange. Sight distance adequacy, particularly at on-ramps; Conflicts for motorists pulling onto the shoulder; The minimum shoulder width for BBS operations is 3.0 m Loss of safe evasive movement shelter area; (10 ft). Buses are allowed to operate at safe speeds of up to Need for bus driver training; 70 kph (44 mph). Speed differential; Impact on adjacent lane motorists; Return merge distance adequacy; BUS USE OF SHOULDER CONCERNS Shoulder area debris hazards; Reduced clearance for buses at bridge abutments; and Survey respondents were asked what types of concerns they Drainage and hydroplaning. have regarding the design, operation, and implementation of the bus use of shoulders concept. The following types of con- The first five of these safety concerns relate to potential cerns were expressed. traffic conflicts along the shoulder lane. Motorists exiting from the general traffic lane will not be expecting a bus Loss of Intended Shoulder Functions approaching from behind using the shoulder. Motorists need- ing to pull onto the shoulder similarly will not be expecting Shoulders provide a range of important functions. Use of the traffic using the shoulder. Most motorists pulling onto the shoulder by buses at times when the highway is congested shoulder use their turn signals, which would warn buses using and moving slowly compromises these functions, even if the shoulder as well as motorists that are following in general shoulders are limited to bus use only. Four shoulder use func- traffic lanes. Traffic entering the highway will not expect traf- tions were identified as concerns by survey respondents. fic using the shoulder lane and typically will have shorter merging sight distances. On occasion, motorists use shoulders Removal and storage of disabled vehicles and accidents, to evade collisions and abrupt changes in traffic speeds. If Emergency vehicle use, buses are using the shoulder lane, this evasion option could be Staging area for maintenance work, and compromised. Establishment of good operating protocols, Snow storage. training of bus drivers, and good signage can help minimize these safety issues, but the more intense use of the highway It was pointed out that highways tended to be most con- right-of-way will inherently increase traffic safety risks. By gested when accidents have occurred, when disabled vehi- limiting use of the shoulders to conditions when general traf- cles are being attended to along the roadside, when highway fic is operating slowly and limiting the speeds of buses using maintenance work was ongoing, and when weather condi- the shoulder facilities, the risks are more manageable. tions are poor (e.g., when it snows). Accident situations also are the times when emergency vehicles most need to use The next three of the safety concerns relate to potential shoulder facilities. impacts on traffic using the general traffic lanes. Unexpected traffic traveling at high speed in the shoulder lane could sur- Some of these functional concerns seem to be based on the prise some motorists and lead to accidents. If the develop- perception that high volumes of vehicles would use the shoul- ment of shoulder use lanes involves narrowing general traffic der and the shoulder itself would become congested. If shoul- lanes to provide a wide shoulder, the narrowed general traf- der use is restricted to bus traffic only and bus drivers were fic lanes will likely lead to increased accident risks (particu- in close radio communications with central dispatch, most of larly at periods of high speed when the shoulder is not being the shoulder use concerns could be effectively addressed. used). The importance of safe design to accommodate the Because no physical barriers would be constructed between the transition from shoulder to general traffic lanes was also shoulder lane and the right-most general traffic lane, buses identified as a concern. With the exception of the narrowing could merge into general traffic lanes to bypass obstructions of general traffic lanes, these safety concerns all appear man- along the shoulder. Advisories to bus drivers could also address ageable using good design and operations practices.