| I. INTERSECTIONS (AT-GRADE) |
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Background and Scope of Handbook Recommendations The single greatest concern in accommodating older road users, both drivers and pedestrians, is the ability of these persons to safely maneuver through intersections. The findings of one widely cited analysis of nationwide accident data (Hauer, 1988), illustrated below, reveal the relationship between injuries and fatalities at intersections during the period 19831985 in the United States, as a function of age and road user type (driver or pedestrian). |

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For drivers 80 years and older, more than half of fatal accidents occur at intersections, compared
with 24 percent or less for drivers up to 50 years of age (Insurance Institute for Highway Safety,
1993). These findings reinforce a long-standing recognition that driving situations involving
complex speed-distance judgments under time constraintsthe typical scenario for intersection
operationsare more problematic for older drivers and pedestrians than for their younger
counterparts (Waller, House, and Stewart, 1977). Other studies within the large body of evidence
showing dramatic increases in intersection accident involvements as driver age increases have
revealed detailed patterns of data associating specific accident types and vehicle movements with
particular age groups, and in some cases have linked such patterns to the driving task demands in a
given maneuver situation (see Campbell, 1993; Council and Zegeer, 1992; Staplin and Lyles,
1991). Another approach to characterizing older driver problems at intersections was employed by Brainin (1980), who used in-car observations of driving behavior with 17 drivers ages 2544, 81 drivers ages 6069, and 18 drivers age 70 and older, on a standardized test route. The two older age groups showed more difficulty making right and left turns at intersections and negotiating traffic signals. The left-turn problems resulted from a lack of sufficient caution and poor positioning on the road during the turn. Right-turn difficulties were primarily a result of failing to signal. Errors demonstrated at STOP signs included failing to make complete stops, poor vehicle positioning at STOP signs, and jerky and abrupt stops. Errors demonstrated at traffic signals included stops that were either jerky and abrupt, failure to stop when required, and failure to show sufficient caution during the intersection approach. Complementing accident analyses and observational studies with subjective reports of intersection driving difficulties, a statewide survey of 664 senior drivers by Benekohal, Resende, Shim, Michaels, and Weeks (1992) found that the following activities become more difficult for drivers as they grow older (with proportion of drivers responding in parentheses):
Reading street signs in town (27 percent).
Lighting at intersections (62 percent). Comparisons of responses from drivers ages 6668 versus those age 77 and older showed that the older group had more difficulty following pavement markings, finding the beginning of the left-turn lane, and driving across intersections. Similarly, the level of difficulty for reading street signs and making left turns at intersections increased with increasing senior driver age. Turning left at intersections was perceived as a complex driving task. This was made more difficult when raised channelization providing visual cues was absent, and only pavement markings designated which were through lanes versus turning lanes ahead. For the oldest age group, pavement markings at intersections were the most important item, followed by the number of left-turn lanes, concrete guides, and intersection lighting. A study of older road users completed in 1996 provides evidence that the single most challenging aspect of intersection negotiation for this group is performing left turns during the permitted (green ball) signal phase (Staplin, Harkey, Lococo, and Tarawneh, 1997). During focus group discussions conducted by Benekohal et al. (1992), older drivers reported that intersections with too many islands are confusing, that raised curbs that are unpainted are difficult to see, and that textured pavements (rumble strips) are of value as a warning of upcoming raised medians, approaches to (hidden or flashing red) signals, and the roadway edge/shoulder lane boundary. Regarding traffic signals, study subjects indicated a clear preference to turn left on a protected arrow phase, rather than making "permitted phase" turns. When turning during a permitted phase (green ball) signal operation, they reported waiting for a large gap before making a turn, which frustrates drivers in back of them and causes the drivers behind to go around them or blow their horns. A general finding here was the need for more time to react. Additional insight into the problems older drivers experience at intersections was provided by focus group responses from 81 older drivers in the Staplin et al. study (1997). The most commonly reported problems are listed below:
Difficulty in turning head at skewed (non-90-degree) angles to view intersecting traffic. Although these problems are by no means unique to older drivers, the various functional deficits associated with aging result in exaggerated levels of difficulty for this user group. Finally, the analysis by Council and Zegeer (1992) included an examination of pedestrian accidents and the collision types in which older pedestrians were overinvolved. The results showed older pedestrians to be overrepresented in both right- and left-turn accidents. The young-elderly (ages 6574) were most likely to be struck by a vehicle turning right, whereas the old-elderly (age 75 and older) were more likely to be struck by a left-turning vehicle. This section will provide recommendations to enhance the performance of diminished-capacity drivers as they approach and travel through intersections, for 16 different design elements: A. intersecting angle (skew); B. receiving lane (throat) width for turning operations; C. channelization; D. intersection sight distance (sight triangle); E. opposite (single) left-turn lane geometry, signing, and delineation; F. edge treatments/delineation of curbs, medians, and obstacles; G. curb radius; H. traffic control for left-turn movements at signalized intersections; I. traffic control for right-turn/right-turn-on-red (RTOR) movements at signalized intersections; J. street-name signage; K. one-way/wrong-way signage; L. stop- and yield-controlled intersection signage; M. devices for lane assignment on intersection approach; N. traffic signal performance issues; O. fixed lighting installations; and P. pedestrian control devices. The Handbook recommendations that follow are supported by material presented later in the "Rationale and Supporting Evidence" section under the "Intersections (At-Grade)" heading. |
| Recommendations by Design Element |
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The rationale and supporting evidence for this recommendation can be found by clicking here.
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Case I: No Control
2b. Where the provision of unrestricted sight distance is not feasible, ISD values for left-turning traffic that must yield to opposing traffic on the major roadway (ISD Case V) should be computed using the modified AASHTO model, as follows:
ISD = 1.47 V (J +ta) where: ISD = intersection sight distance (feet for English
V = major roadway operating speed (mi/h for
English equation; km/h for metric equation). The rationale and supporting evidence for these recommendations can be found by clicking here.
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where: ISD = intersection sight distance (feet for English
equation; meters for metric equation).
4a. In the implementation of (advance) DIVIDED HIGHWAY CROSSING signs, and WRONG WAY, DO NOT ENTER, and ONE WAY signs at the intersection, as per MUTCD (Federal Highway Administration, 1988) specifications, sign sizes larger than MUTCD standard sizes (e.g., MUTCD expressway size for DO NOT ENTER [900 x 900 mm] and MUTCD special size for WRONG WAY [1050 x 750 mm]) are recommended, as is high-intensity sheeting. 4b. Lane-use arrows for channelized left-turn lanes are recommended, and reflectorized treatments should be used wherever practical; otherwise, white painted pavement markings should be used. 4c. Pavement markings which scribe a path through the turn are recommended to reduce the likelihood for the wrong-way movement. 4d. The use of a white stop bar 600 mm (24 in) in width is recommended at the end of the channelized left-turn lane as a countermeasure to aid in preventing a potential wrong-way movement. 4e. Placement of 7-m (23.5-ft) wrong-way arrows in the through lanes is recommended for wrong-way traffic control at locations determined to have a special need, as specified in the MUTCD, section 2E-40. 4f. Delineation of median noses using reflectorized paint and other treatments to increase their visibility and improve driver understanding of the intersection design and function is recommended. The diagram presented on the facing page illustrates the countermeasures as described above in Handbook Recommendations E(4a)(4f). The rationale and supporting evidence for these recommendations can be found by clicking here. |

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Recommended signing and delineation treatments for intersections with medians
9 m (30 ft) wide or wider, and medians with channelized left-turn lanes, to
reduce the potential for wrong-way movements for drivers turning left from the
minor roadway.
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The rationale and supporting evidence for these recommendations can be found by clicking here.
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The rationale and supporting evidence for these recommendations can be found by clicking here.
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The rationale and supporting evidence for these recommendations can be found
by clicking here.
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The consistent posting of lane-use control signs plus application of lane-use arrow pavement markings at a preview distance of at least 5 s (at operating speed) in advance of a signalized intersection is recommended, regardless of the specific lighting, channelization, or delineation treatments implemented at the intersection. Signs should be mounted overhead wherever practical, but they may be shoulder- and/or median-mounted in other cases. The rationale and supporting evidence for these recommendations can be found by clicking here.
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