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                        Handbook for Designing Roadways for the Aging Population


            
            In This Section
        Other Safety Areas
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                                Overview
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                Pavement Markings
                Roadway Lighting
                Focused Approach to Safety
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                Chapter 2. Intersections
This section of the *Handbook* provides treatments for 16 different design elements in order to accommodate the needs and enhance the performance of road users with age-related diminished capabilities as they approach and negotiate intersections. Also, after the last element, eight additional promising practices are provided. Drawings are for illustrative purposes only; they are not to scale and should not be used for design purposes.

Proven Practices

Intersecting Angle (Skew)
	Receiving Lane (Throat) Width
	Channelization
	Intersection Sight Distance
	Offset Left-Turn Lanes
	Delineation of Edge Lines and Curbs
	Curb Radius
	Left-Turn Traffic Control for Signalized Intersections
	Right-Turn Traffic Control for Signalized Intersections
	Street Name Signs
	Stop and Yield Signs
	Lane Assignment on Intersection Approach
	Traffic Signals
	Intersection Lighting
	Pedestrian Crossings
	RoundaboutsPromising Practices

Right Turn Channelization Design
	Combination Lane-Use/Destination Overhead Guide Signs
	Signal Head Visibility
	High Visibility Crosswalks
	Supplemental Pavement Markings for Stop and Yield Signs
	Reduced Left-Turn-Conflict Intersections
	Accessible Pedestrian Signal (APS) Treatments
	Flashing Yellow ArrowThe single greatest concern in accommodating aging road users, both drivers and pedestrians, is the ability of these persons to negotiate intersections safely. For at least two decades, safety experts have keyed on relationships of age and road user type (driver or pedestrian) to understand injury and fatal crash experience at intersections in the United States. The findings of one widely cited analysis of nationwide crash data (Hauer, 1988) are shown in Figure 2.



Figure 2. Two bar charts showing the percentage of injuries and fatalities to drivers and pedestrians at intersections by age group.  The chart on the left shows data for drivers; 48 percent of injuries and 18 percent of fatalities for drivers aged 26 to 64 occur at intersections, compared to 60 percent of injuries and 37 percent of fatalities for drivers 65 and older.  The chart on the right shows data for pedestrians; 26 percent of injuries and 18 percent of fatalities for drivers aged 26 to 64 occur at i


Figure 2. Percentage of crashes involving drivers and pedestrians by age at intersections (Hauer, 1988)

The figure illustrates that aging drivers and aging pedestrians are involved in a higher percentage of injury and fatal incidents at intersections.

These same relationships endure today. A higher proportion of passenger vehicle drivers age 70 and older are involved in fatal multiple-vehicle crashes at intersections (40%) than drivers younger than age 70 (22%) (IIHS, 2007). While the number of fatalities, both overall and among aging road users, has declined in recent years, people age 65 and older are still involved in a disproportionate share of fatalities compared to the population as a whole (see Table 5). The number of aging drivers has increased substantially, making up a larger share of the driving population. Therefore, while people age 65 and older make up about 13 percent of the nation's population, they represent about 16 percent of drivers, 16 percent of driver fatalities, and 19 percent of pedestrian fatalities (FARS, 2013). These findings reinforce a long-standing recognition that driving situations involving complex speed-distance judgments under time constraints—the typical scenario for intersection operations—are more problematic for aging road users than for their younger counterparts. Other studies within the large body of evidence showing dramatic increases in intersection crash involvements as driver age increases have associated specific crash types and vehicle movements with particular age groups, linked in some cases to the driving task demands for a given maneuver (Campbell, 1993; Council and Zegeer, 1992; Staplin and Lyles, 1991).

Table 5. Involvement of the Older Population in Traffic Fatalities by Gender, 2002 and 2011 (FARS, 2013)
	2002
			2011
			Percentage Change, 2002–2011Total
			Age 65+
			Percentage of Total
			Total
			Age 65+
			Percentage of Total
			Total
			Age 65+Population (Thousands)Total
			287,625
			35,522
			12.4
			311,592
			41,394
			13.3
			8
			17Male
			141,231
			14,764
			10.5
			153,291
			17,943
			11.7
			9
			22Female
			146,395
			20,758
			14.2
			158,301
			23,451
			14.8
			8
			13Drivers Involved in Fatal CrashesTotal*
			58,113
			6,323
			10.9
			43,668
			5,469
			12.5
			-25
			-14Male
			42,377
			4,340
			10.2
			31,806
			3,769
			11.8
			-25
			-13Female
			14,999
			1,982
			13.2
			11,209
			1,700
			15.2
			-25
			-14Driver FatalitiesTotal*
			26,659
			3,984
			14.9
			20,753
			3,402
			16.4
			-22
			-15Male
			19,859
			2,704
			13.6
			15,868
			2,316
			14.6
			-20
			-14Female
			6,799
			1,279
			18.8
			4,881
			1,086
			22.2
			-28
			-15Total Traffic FatalitiesTotal*
			43,005
			6,680
			15.5
			32,367
			5,401
			16.7
			-25
			-19Male
			29,466
			3,840
			13.0
			22,860
			3,261
			14.3
			-22
			-15Female
			13,529
			2,838
			21.0
			9,499
			2,140
			22.5
			-30
			-25Occupant FatalitiesTotal*
			37,375
			5,541
			14.8
			27,060
			4,417
			16.3
			-28
			-20Male
			25,491
			3,154
			12.4
			19,053
			2,617
			13.7
			-25
			-17Female
			11,875
			2,386
			20.1
			8,000
			1,800
			22.5
			-33
			-25Pedestrian FatalitiesTotal*
			4,851
			1,064
			21.9
			4,432
			845
			19.1
			-9
			-21Male
			3,298
			619
			18.8
			3,086
			522
			16.9
			-6
			-16Female
			1,552
			444
			28.6
			1,345
			323
			24.0
			-13
			-27Passenger Vehicle Occupant FatalitiesTotal*
			32,843
			5,314
			16.2
			21,253
			3,970
			18.7
			-35
			-25Male
			21,431
			2,959
			13.8
			13,811
			2,208
			16.0
			-36
			-25Female
			11,403
			2,354
			20.6
			7,435
			1,762
			23.7
			-35
			-25Motorcyclist FatalitiesTotal
			3,270
			96
			2.9
			4,612
			301
			6.5
			41
			214Male
			2,961
			89
			3.0
			4,181
			285
			6.8
			41
			220Female
			309
			7
			2.3
			431
			16
			3.7
			39
			129Pedalcyclist FatalitiesTotal
			665
			56
			8.4
			677
			90
			13.3
			2
			61Male
			592
			53
			9.0
			578
			82
			14.2
			-2
			55Female
			73
			3
			4.1
			99
			8
			8.1
			36
			167* Total includes unknown gender.

Complementing crash analyses and observational studies with subjective reports of intersection driving difficulties, a statewide survey of 664 aging drivers by Benekohal, et al. (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).
	Driving across an intersection (21 percent).
	Finding the beginning of a left-turn lane at an intersection (20 percent).
	Making a left turn at an intersection (19 percent).
	Following pavement markings (17 percent).
	Responding to traffic signals (12 percent).Benekohal et al. (1992) also found that the following highway features become more important to drivers as they age (with proportion of drivers responding in parentheses):

Lighting at intersections (62 percent).
	Pavement markings at intersections (57 percent).
	Number of left-turn lanes at an intersection (55 percent).
	Width of travel lanes (51 percent).
	Concrete lane guides (raised channelization) for turns at intersections (47 percent).
	Size of traffic signals at intersections (42 percent).Comparisons of responses from drivers ages 66–68 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 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 aging 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 permissive signal phase (Staplin, et al., 1997).

During focus group discussions (Benekohal et al., 1992), aging drivers reported that intersections with too many islands are confusing; raised curbs that are unpainted (unmarked) are difficult to see; and 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. Study subjects indicated a clear preference for turning left on a protected arrow phase, rather than making permissive-phase turns. When turning during a permissive phase of signal operation, they reported waiting for a large gap before making a turn, which frustrates drivers behind them. A key finding was the need for more time to react.

Additional insight into the problems aging drivers experience at intersections was provided by focus group responses from 81 aging drivers (Staplin et al., 1997). The most commonly reported problems are listed below:

Difficulty in turning their heads at skewed (non-90-degree) angles to view intersecting traffic.
	Difficulty in smoothly performing turning movements at tight corners.
	Hitting raised concrete barriers such as channelizing islands in the rain and at night.
	Finding oneself positioned in the wrong lane—especially a "turn-only" lane—during an intersection approach, due to poor visibility (maintenance) of pavement markings or the obstruction of roadside signs designed to inform drivers of intersection traffic patterns.
	Difficulty at the end of an auxiliary (right) turn lane in seeing potential conflicts well and quickly enough to smoothly merge with adjacent-lane traffic.
	Merging with adjacent-lane traffic at a pavement width reduction, when the lane drop occurs near (i.e., within 500 ft of) an intersection.For aging pedestrians, age-related diminished capabilities may make it more difficult to negotiate intersections. Aging pedestrians face a variety of concerns, including decreased visual acuity, increased risk of falls, slowed walking and crossing speeds, and decreased ability to judge safe gaps and avoid turning vehicles.

Lighting and visibility at intersections are increasingly important to pedestrians as they age. In a survey of aging pedestrians (average age of 75) involved in crashes, 63 percent reported that they failed to see the vehicle that hit them, or to see it in time to take evasive action (Sheppard and Pattinson, 1986). Knoblauch, et al. (1995) noted that difficulty seeing a vehicle against a (complex) street background may occur with vehicles of certain colors, causing them to blend in with their background. Reductions in visual acuity make it more difficult for aging pedestrians to read the crossing signal as well (Bailey, et al., 1992).

With increasing age, there is a concurrent loss of physical strength, joint flexibility, agility, balance, coordination and motor skills, and stamina. These losses contribute to difficulty negotiating curbs and an increased risk of falling as a result of undetected surface irregularities in the pavement and inaccurate estimation of curb heights (Clark, Lord, and Webster, 1993).

The physical limitations of aging pedestrians result in a greater likelihood to delay before crossing; to wait for longer gaps between vehicles before attempting to cross the road (Tobey, Shungman, and Knoblauch, 1983); to spend more time at the curb; to take longer to cross the road (Hoxie and Rubenstein, 1994; Knoblauch, Nitzburg, Dewar, et al., 1995); and to make more head movements before and during crossing (Wilson and Grayson, 1980). Parsonson (1992) reported that the State of Delaware has found that pedestrians do not react well to the short WALK and long flashing DONT WALK timing pattern.

Turning vehicles are also a concern for aging pedestrians. The loss of peripheral vision and "useful field of view" increases an aging pedestrian's chances of not detecting approaching and turning vehicles from the side. The analysis by Council and Zegeer (1992) included an examination of vehicle-pedestrian crashes and the collision types in which aging pedestrians were over-involved. The results showed aging pedestrians to be overrepresented in both right- and left-turn crashes. The young-elderly (ages 65-74) 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.

Together, these findings from research on aging road users reinforce the overriding design principles to "clarify" and 'simplify" traffic operations at intersections. By providing appropriate advance information about route choices and destinations, clearly identifying lane assignments for allowed maneuvers, and implementing conspicuous and easily comprehensible sign and signal displays for traffic control, engineers can manage workload during intersection approach and negotiation in a manner that benefits road users of all ages. Likewise, the need for intersection geometrics to unambiguously convey path, direction, and speed is universal, and such "positive guidance" is an explicit goal of the treatments presented in this chapter.

Proven Practices1. Intersecting Angle (Skew)

The HSM (page 10-32) defines skew angle as: intersection skew angle (in degrees); the absolute value of the difference between 90 degrees and the actual intersection angle.

A. Unrestricted Right-of-Way

In the design of new facilities or redesign of existing facilities where right-of-way is not restricted, all intersecting roadways should meet at a 90-degree angle (as indicated in Figure 3).

References *: *Green Book*:1, NCHRP 279:1, TEH:1, NCHRP 500-9:1

B. Restricted Right-of-Way

In the design of new facilities or redesign of existing facilities where right-of-way is restricted, intersecting roadways should meet at an angle of not less than 75 degrees (as indicated in Figure 4).

References *: TEH:2

C. Skewed Signalized Intersections

At skewed signalized intersections where the approach leg to the left intersects the driver's approach leg at an angle of less than 75 degrees, prohibit right turn on red (RTOR) (see Figure 5).

References *: TEH:4, *MUTCD*:2

The rationale and supporting evidence for these treatments begins on page 96 of the *Handbook*.

Figure 3. An image of a four-leg intersection where the legs meet at 90-degree angles.


Figure 3. Example 90° angle of intersection

Figure 4. An image of a four-leg intersection where the smallest angle of intersection of the four legs is 75 degrees.


Figure 4. Example 75° angle of intersection



Figure 5. An image of a four-leg 75-degree intersection where 'NO TURN ON RED' (MUTCD R10-11) signs have been posted on the approaches that have the 75-degree angle to the left.




Figure 5. Skewed signalized intersection with prohibition of right turn on red

2. Receiving Lane (Throat) Width

A. Minimum Width

Wherever practical, a minimum receiving throat width of 16 ft is recommended. The total width may include a travel lane of 11 to 12 ft and a paved shoulder or bicycle lane of 4 to 5 ft as shown in Figure 6.

References *: NCHRP 279:2, TEH:2

Figure 6. An image of part of an intersection that shows a 16-ft receiving width dimension on the departure from the intersection.  The 16-ft dimension is divided into a travel lane of 11 to 12 ft and a bicycle lane/paved shoulder of 4 to 5 ft.


Figure 6. Recommended receiving lane width

The rationale and supporting evidence for this treatment begins on page 99 of the *Handbook*.

3. Channelization

A. Left- and Right-Turn Lanes

Raised channelization with sloping curbs (see Figure 7) is recommended over channelization accomplished through the use of pavement markings alone (flush) for left- and right-turn lane treatments at intersections on all roadways with operating speeds of less than 45 mph.

References *: *Green Book*:4, NCHRP 279:4, TEH:4, *MUTCD*:4, NCHRP 500-9:4

B. Retroreflective Markings

Where raised channelization is implemented at intersections (see Figure 7) the median and island curb sides and curb horizontal surfaces should be treated with retroreflectorized markings, such as edge lines, painted curbs, or raised pavement markers, and be maintained at a minimum luminance contrast level* as follows:

B-1. With overhead lighting, a contrast of at least 2.0.
	B-2. Without overhead lighting, a contrast of at least 3.0.Contrast should be calculated according to this formula:

Luminance contrast (C) equals the difference between the luminance of the stripe and the luminance of the pavement divided by the luminance of the pavement.


* Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often described as brightness)—especially at night—this may vary greatly for the same object or marking depending upon such factors as the location and intensity of the source of illumination, and the angle at which a driver views it.

References *: *MUTCD*:4, NCHRP 500-9:4

C. Acceleration Lane

If right-turn channelization is present at an intersection, an acceleration lane providing for the acceleration characteristics of passenger cars as delineated in AASHTO (2011) specifications is recommended for operating speeds of 45 mph or greater.

References *: *Green Book*:4

D. Sloping vs. Vertical Curbs

The use of sloping curbs rather than vertical curbs (see Figure 7) for channelization is recommended, except where the curbs surround a pedestrian refuge area or are being used for access control. Vertical curbs should also not be used for channelization on high-speed (i.e., 45 mph or greater) roadways.

References *: *Green Book*:4, NCHRP 279:4

E. Pedestrian Refuge Island

If right-turn channelization is present and pedestrian traffic may be expected based on surrounding land use, it is recommended that an adjacent pedestrian refuge island, conforming to *MUTCD* (2009) and AASHTO (2011) specifications, be provided.

References *: *Green Book*:1, NCHRP 279:3, *MUTCD*:1

F. Median Channelization

To reduce unexpected midblock conflicts with opposing vehicles, the use of channelized left-turn lanes in combination with continuous raisedcurb medians is recommended instead of center, two-way, left-turn lanes (TWLTL) for new construction or reconstruction where average daily traffic volumes exceed 20,000 vehicles per day, or for remediation where there is a demonstrated crash problem, or wherever a need is demonstrated through engineering study.

References *: *Green Book*:4, NCHRP 279:4



Figure 7 (top).  Two pictures showing curb treatments.  The picture on top shows a vertical curb around a median island; the picture on the bottom shows a sloping curb around a median island.




Figure 7 (bottom).  Two pictures showing curb treatments.  The picture on top shows a vertical curb around a median island; the picture on the bottom shows a sloping curb around a median island.


Figure 7. Vertical Curb (top), Sloping Curb (bottom)

The rationale and supporting evidence for these treatments begins on page 102 of the *Handbook*.

4. Intersection Sight Distance

A. Gap Value

It is recommended that a gap of no less than 8.0 s, plus 0.5 s for each additional lane crossed, be used in intersection sight distance (ISD) calculations to accommodate the slower decision-making and maneuver times of aging drivers for the following cases:

Cases B1, B2, and B3 – stop-control on the minor road,
	Cases C1 and C2 – yield control on the minor road,
	Case D – signalized with permissive left-turn phases and/or where RTOR is permitted and/or which are placed on flashing operations at night, and
	Case F – left turns from a major roadway.Note: Cases refer to the intersection control cases defined in the AASHTO *Green Book* (2011).

References *: *Green Book*:1

The rationale and supporting evidence for these treatments begins on page 107 of the *Handbook*.

5. Offset Left-Turn Lanes

A. Full Offset – Opposing Cars

Left-turn lanes should be positively offset (as shown in Figure 8) at least 4 ft to the left of the opposing left-turn lane to achieve the desired sight distance for the left-turning driver. This will provide a margin of safety for aging drivers who, as a group, do not position themselves to the far left within the lane and within the intersection before initiating a left turn.

References *: *Green Book*:1, NCHRP 279:4, TEH:4, NCHRP 500-9:4



Figure 8. An image showing a four-leg intersection where the left-turn lanes on the major road have positive offset and are separated from the adjacent through lanes.




Figure 8. Left-turn lanes with positive offset

B. Full Offset – Opposing Heavy Trucks

At intersections where engineering judgment indicates a high probability of heavy trucks as the opposing left-turning vehicles, the positive offset is recommended to be 5.5 ft to achieve the desired sight distance.

References *: *Green Book*:4, NCHRP 279:4, TEH:4, NCHRP 500-9:4

C. Minimum Offset

At locations where the full offset distances cannot be obtained, it is recommended that the minimum offset distances shown in Table 6 be provided to achieve minimum required sight distances according to design speed. It is recommended that the "Opposing Truck" values be used where the opposing left-turn traffic includes a moderate to heavy volume of large trucks.

References *: *Green Book*:4, NCHRP 279:4, TEH:4, NCHRP 500-9:4

Table 6. Minimum offset distances for left-turn lanes.
	Design Speed (mph)
			Minimum Offset (ft)Opposing Car
			Opposing Truck≤30
			0.8
			3.035
			1.4
			3.540
			1.8
			3.845
			2.1
			4.150
			2.4
			4.255
			2.6
			4.460
			2.7
			4.565
			2.8
			4.670
			2.9
			4.71 ft = 0.305 m

D. Signs and Markings

At intersections where the left-turn lane treatment results in channelized offset left-turn lanes (e.g., a parallel or tapered left-turn lane between two medians), the following countermeasures (see Figure 9) are recommended to reduce the potential for wrong-way maneuvers by drivers turning left from a stop-controlled intersecting minor roadway:

D-1. Largest practical sign sizes as specified in the *MUTCD* (2009) for DIVIDED HIGHWAY CROSSING, WRONG WAY, DO NOT ENTER, KEEP RIGHT, and ONE WAY signs.

	References *: TEH:4, *MUTCD*:3, NCHRP 500-9:4
	D-2. For the signs listed above, use prismatic retroreflective sheeting, to provide increased sign conspicuity and legibility for older drivers. Ensure these signs are replaced before they meet the minimum sign retroreflectivity levels, which includes white on red signs having a contrast ratio of at least 3:1.
	References *: *MUTCD*:1, NCHRP:4
	D-3. Retroreflective lane-use arrows.
	References *: *MUTCD*:1, NCHRP 500-9:4
	D-4. Retroreflective pavement marking extensions of the center line that scribe a path through the turn, except where extensions for opposing movements cross.
	References *: *MUTCD*:3, NCHRP 500-9:4
	D-5. Placement of 23.5-ft- long retroreflective wrong-way arrows in the through lanes at locations determined to have a special need, as specified in the *MUTCD* (2009), Sections 3B.19 and 2E-50.
	References *: *MUTCD*:3, NCHRP 500-9:4
	D-6. Delineation of median noses using retroreflective treatments to increase their visibility and improve driver understanding of the intersection design and function.
	References *: *Green Book*:1, *MUTCD*:2, NCHRP 500-9:4

Figure 9. An image showing recommended signs and pavement markings for an intersection on a divided roadway with channelized offset left-turn lanes.




Figure 9. Recommended signs and markings for intersections with channelized offset left-turn lanes

E. Pedestrian Accommodations

At intersections where there are high pedestrian volumes, and the offset left-turn treatment results in a crossing width that would require a pedestrian walking at 3.0 ft/s to cross in two stages, the following is recommended to create a pedestrian crossing island (or refuge area), as shown in Figure 10:

E-1. Flush (painted) channelization is used to separate the left-turn lane and adjacent through lanes.
	E-2. Raised channelization with a vertical curb and a minimum width of 6 ft is used to separate the left-turn lane from opposing travel lanes. While a 6-ft width is the minimum, there are advantages to providing wider islands where possible. Sloped curbs should be used instead of vertical curbs for channelization on high-speed (i.e., 45 mph or greater) roadways.References *: *Green Book*:1, *MUTCD*:2

The rationale and supporting evidence for these treatments begins on page 122 of the *Handbook*.

Figure 10. An image showing the recommended configuration of a pedestrian crossing refuge island located in the median adjacent to a left-turn lane.  Specifically identified is the dimension of a 6-ft minimum width for the island.


Figure 10. Pedestrian Crossing Island (or Refuge Area)

6. Delineation of Edge Lines and Curbs

A. Visibility

A minimum in-service luminance contrast level between the marked edge of the roadway and the road surface should be maintained as follows:

A-1. At intersections with overhead lighting, a contrast of 2.0 or higher.
	A-2. At intersections without overhead lighting, a contrast of 3.0 or higher.Contrast should be calculated according to this formula:

Luminance contrast (C) equals the difference between the luminance of the stripe and the luminance of the pavement divided by the luminance of the pavement.


* Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often described as brightness)—especially at night—this may vary greatly for the same object or marking depending upon such factors as the location and intensity of the source of illumination, and the angle at which a driver views it.

References *: *MUTCD*:4, RLH:4

B. Intersection Curbs

Curbs at intersections (including median islands and other raised channelization) should be delineated on their vertical face and at least a portion of the top surface, in addition to the provision of a marked edge line on the road surface (see Figure 11).

The use of a Keep Right (R4-7 Series) or a Double Arrow (W12-1) sign with the addition of a low-mounted Type 1 Object Marker (OM1-1) near the median and channelizing island noses, respectively, could also be helpful to aging road users. These signs are optional and can be used if they are warranted. Since markings primarily supplement signing, this treatment should be placed in addition to the signing available for these locations.

References *: *Green Book*:1, *MUTCD*:1

Figure 11. A picture of a raised median island with yellow surfacing on the vertical curb and the top of the nose of the island.


Figure 11. Raised median island with yellow marking on the vertical face and top surface

The rationale and supporting evidence for these treatments begins on page 129 of the *Handbook*.

7. Curb Radius

A. Simple Radius

Where roadways intersect at 90 degrees and are joined with a simple radius curve, a corner curb radius in the range of 25 ft to 30 ft is recommended to: (a) facilitate vehicle turning movements, (b) moderate the speed of turning vehicles, and (c) avoid unnecessary lengthening of pedestrian crossing distances (see Simple Curve in Figure 12).

References *: AASHTO:1, NCHRP 279:1

B. Accommodation of Heavy Vehicles

When it is necessary to accommodate turning movements by large trucks, the use of offsets, tapers, and compound curves is recommended in place of larger simple radii (e.g., 75 ft or more) to minimize pedestrian crossing distances (see Figure 12).

References *: AASHTO:1, NCHRP 279:4, TEH:4



Figure 12. An image showing three alternatives for a curb radius at hypothetical intersection.  The three alternatives are a simple curve with a 25-ft radius, a 20-ft curve with 1-to-10 tapers and 2.5-ft offsets, and a 3-centered compound curve with radii of 100 ft, 20 ft, and 100 ft.




Figure 12. Comparison of curb radii

The rationale and supporting evidence for these treatments begins on page 132 of the *Handbook*.

8. Left-Turn Traffic Control for Signalized Intersections

A. Protected-Only Left-Turn Phasing

The use of protected-only left-turn operations is recommended for all left-turning movements, whenever appropriate. In particular, protected-only left-turn phasing should be considered where minimum intersection sight distance requirements are not achieved through the use of offset left-turn lanes (see Design Element 5) or other geometric design features, or where a pattern of permissive left-turn crashes occurs.

References *: *Green Book*:4, TEH:1, *MUTCD*:1

B. Permissive Left-Turn Signing

If circular green is used as the permissive indication of a protected/permissive left-turn, consistent use of the *MUTCD* R10-12 sign, (LEFT TURN YIELD ON GREEN

solid green ball/circle representing the round green light in a traffic signal


) is recommended, with overhead placement preferred at the intersection adjacent to the left-turn signal face (see Figure 13).

References *: TEH:4, *MUTCD*:1



Figure 13. A picture of a 'LEFT TURN YIELD ON GREEN BALL' (MUTCD 10-12) sign on a signal mast arm adjacent to the left-turn signal head, which also shows a green ball display.




Figure 13. MUTCD R10-12 sign adjacent to left-turn signal face

C. Advance Signing

Where practical, an additional R10-12 sign (i.e., in addition to the R10-12 sign adjacent to the signal face) should be placed in advance of the intersection to advise left-turning drivers of permissive signal operation. The sign should be displayed at a 3-s preview distance before the intersection, or at the beginning of the left-turn lane, as per engineering judgment, accompanied by an AT SIGNAL (R10-31P) supplemental plaque as shown in Figure 14. [See time-speed-distance table on page 5.]

References *: AASHTO:3, *MUTCD*:1, NCHRP 500-9:4

Figure 14. An image of an 'AT SIGNAL' (MUTCD R10-31P) plaque.


Figure 14. (*MUTCD* R10-31P)

D. Lead versus Lag Phasing

A leading protected left-turn phase is recommended wherever protected left-turn signal operation is implemented (as opposed to a lagging protected left-turn phase).

References *: TEH:2, *MUTCD*:2

The rationale and supporting evidence for these treatments begins on page 135 of the *Handbook*.

9. Right-Turn Traffic Control for Signalized Intersections

A. Turn Prohibition

At signalized intersections where a right turn on red is prohibited, a supplemental NO TURN ON RED sign, using the *MUTCD* R10-11 design as shown in Figure 15, should be placed at a location on either the near or opposite side of the intersection where, per engineering judgment, it will be most conspicuous. This supplemental NO TURN ON RED sign is in addition to the *MUTCD* recommended practice of installing an R10-11 series sign near the appropriate signal head.

References *: TEH:4, *MUTCD*: 1

Figure 2. Two bar charts showing the percentage of injuries and fatalities to drivers and pedestrians at intersections by age group.  The chart on the left shows data for drivers; 48 percent of injuries and 18 percent of fatalities for drivers aged 26 to 64 occur at intersections, compared to 60 percent of injuries and 37 percent of fatalities for drivers 65 and older.  The chart on the right shows data for pedestrians; 26 percent of injuries and 18 percent of fatalities for drivers aged 26 to 64 occur at i


Figure 15. (*MUTCD* R10-11)

B. Skewed Signalized Intersections

At skewed signalized intersections where the approach leg to the left intersects the driver's approach leg at an angle of less than 75 degrees (as illustrated in Figure 16), prohibit right turn on red (RTOR).

References *: TEH:4, *MUTCD*:1



Figure 16. An image of a four-leg 75-degree intersection where 'NO TURN ON RED' (MUTCD R10-11) signs have been posted on the approaches that have the 75-degree angle to the left.




Figure 16. Skewed signalized intersection with prohibition of right turn on red

C. Pedestrian Protection

The posting of *MUTCD* standard R10-15 signs, Turning Vehicles Yield to Pedestrians (shown in Figure 17) is recommended wherever engineering judgment indicates a clear potential for right-turning vehicles to come into conflict with crossing pedestrians. (Note that a yellow background color may be used instead of fluorescent yellow-green for this sign.)

References *: *MUTCD*:1

Figure 17. An image of a 'Turning Vehicles Yield to Pedestrians' (MUTCD R10-15) sign.


Figure 17. (*MUTCD* R10-15)

The rationale and supporting evidence for these treatments begins on page 148 of the *Handbook*.

10. Street Name Signs

A. Letter Heights and Sign Border

To accommodate the reduction in visual acuity associated with increasing age, minimum letter heights of 6 in for uppercase letters and 4.5 in for lowercase letters are recommended for use on ground-mounted street-name signs (*MUTCD* D3-1, as shown in Figure 18) on all roads where the posted speed limit is at or below 25 mph. On all roads where the posted speed limit is greater than 25 mph, letter heights of 8 in for uppercase letters and 6 in for lowercase letters should be used.

The use of overhead-mounted street-name signs is recommended at major intersections as a supplement to ground-mounted street-name signs. Minimum letter heights of 12 in for uppercase letters and 9 in for lowercase letters are recommended by the *MUTCD*. In the design of street-name signs, the use of larger letter heights may require a larger sign panel. The border may be eliminated on street-name signs if necessary to minimize sign panel size while accommodating the larger letter size.

References *: *MUTCD*:1, NCHRP 500-9:4

Figure 18. An image of a street name (MUTCD D3-1) sign that reads 'E Main St'.


Figure 18. (*MUTCD* D3-1)

B. Advance Street-Name Plaque

Wherever an advance intersection warning sign is installed (*MUTCD* W2 series) it should be accompanied by an advance street name plaque (W16-8P or W16-8aP) using minimum letter heights of 6 in for uppercase letters and 4.5 in for lowercase letters (see Figure 19). Where an advance traffic control sign (*MUTCD* W3 series) is installed on a multi-lane approach, an advance street name plaque (W16-8P or W16-8aP), using the same minimum letter heights described above, should be considered.

References *: *MUTCD*:2, NCHRP 500-9:4

Figure 19. An image of a symbolic Intersection Warning (MUTCD W2-1) sign above a supplemental advance street name (MUTCD W16-8P) plaque that reads 'First St'.


Figure 19. Intersection Warning W2-1 Sign and W16-8P Supplemental Advance Street Name Plaque

C. Advance Street-Name Sign

In the absence of an advance intersection warning sign or advance traffic control sign (with accompanying advance street-name plaque), the use of advance street-name signs (*MUTCD* D3-2) for major intersections is recommended, with turn bays to provide adequate preparation time for any lane change and/or turning maneuvers (see Figure 20).

References *: *MUTCD*:1, NCHRP 500-9:1

D. Directional Street-Name Sign

When different street names are used for different directions of travel on a crossroad, the names should be separated and accompanied by directional arrows on both advance and intersection street-name signs, as shown in Figure 20.

References *: *MUTCD*:1



Figure 20. An image of three options for directional street-name (MUTCD D3-2) signs.  The sign on top reads 'Shady Grove Rd Next Intersection'.  The sign in the middle reads, from top to bottom, (left arrow) 'Scott Blvd', 'Lincoln Ave' (right arrow), and 'Next Signal'.  The sign on the bottom reads (left arrow) 'Scott Blvd' 'Lincoln Ave' (right arrow).




Figure 20. (*MUTCD* D3-2)

E. Retroreflectivity

For ground-mounted street-name signs installed at intersections in areas of intensive land use, complex design features, and heavy traffic, prismatic retroreflective sheeting that provides for high retroreflectance should be used to provide increased sign conspicuity and legibility for aging drivers. The sheeting should be replaced well before it reaches the minimum levels designated in the current MUTCD (Section 2A.08 in the 2009 MUTCD).

References *: *MUTCD*:1

The rationale and supporting evidence for these treatments begins on page 152 of the *Handbook*.

11. Stop and Yield Signs

Treatments to improve the safe use of intersections by aging drivers, where the need for stop control or yield control has already been determined, include the following:

A. Sign Size

The use of standard size (30-in for single lane applications, 36-in for multi-lane applications) STOP (R1-1) and standard size (36-in for single lane applications, 48-in for multi-lane applications, 60-in for freeway applications) YIELD (R1-2) signs, as a minimum, is required by the 2009 *MUTCD* wherever these devices are implemented, with the option of using larger R1-1 (36-in for single lane applications, or 48-in in any location) signs where engineering judgment indicates that greater emphasis or visibility is required.

References *: *MUTCD*:1

B. Retroreflectivity

A minimum sign background (red area) retroreflectivity level (i.e., coefficient of retroreflection [RA]) for STOP (R1-1) and YIELD (R1-2) signs is as follows:

B-1. 12 cd/lux/m2 for roads with operating speeds lower than 40 mph.
	B-2. 24 cd/lux/m2 for roads with operating speeds of 40 mph or higher.Signs with an RA below these levels should be replaced.

References *: TEH:4, *MUTCD*:1

C. Supplemental Warning Sign

The use of a 30-in x 18-in supplemental warning sign panel (*MUTCD* W4-4P) as illustrated in Figure 21, mounted below the STOP (R1-1) sign, is recommended for two-way stop-controlled intersection sites selected on the basis of crash experience, where the sight triangle is restricted, and wherever a conversion from four-way stop to two-way stop operations is implemented.

References *: *MUTCD*:1

Figure 21. An image of a 'CROSS TRAFFIC DOES NOT STOP' (MUTCD W4-4P) plaque.


Figure 21. (*MUTCD* W4-4P)

D. Location of Stop Ahead Sign

A STOP AHEAD sign (*MUTCD* W3-1, as shown in Figure 22) should be used where the distance at which the STOP sign is visible is less than the AASHTO stopping sight distance (SSD) at the operating speed, plus an added preview distance of at least 2.5 s. [See time-speed-distance table on page 5.]

References *: *Green Book*:4, TEH:4, *MUTCD*:1, NCHRP 500-9:4

Figure 22. An image of a symbolic Stop Ahead (MUTCD W3-1) sign.


Figure 22. (*MUTCD* W3-1)

E. Transverse Treatments and Supplemental Pavement Markings

Utilize supplemental pavement markings on approaches to stop-controlled or yield-controlled intersections where engineering judgment indicates a special need due to sight restrictions, high approach speeds, or a history of ran-stop-sign crashes. "STOP AHEAD" pavement markings to supplement STOP AHEAD signs and triangular pavement markings to supplement YIELD AHEAD signs are described in MUTCD Section 3B.20 and Figure 32. Transverse pavement striping or rumble strips may also be considered where high approach speeds are a concern.

References *: TEH:4, NCHRP 500-9:3

The rationale and supporting evidence for these treatments begins on page 160 of the *Handbook*.

12. Lane Assignment on Intersection Approach

A. Lane-Use Control Signs

The consistent overhead placement of lane-use control signs (*MUTCD* R3-5 and R3-6 series) at intersections on a signal mast arm or span wire is recommended, as illustrated in Figure 23.

References *: *MUTCD*:1



Figure 23. A picture of a five-lane approach to a signalized intersection at which an advance mast arm has been installed that displays lane-use control signs.  Above the left lane is a left-turn-only Mandatory Movement Lane Control (R3-5) sign and a white-on-green guide sign for East Ohio Highway 161.  Above the next two lanes are through-only Mandatory Movement Lane Control (R3-5a) signs.  Above the two lanes on the right are right-turn-only Mandatory Movement Lane Control (R3-5R) signs; above the rightmo




Figure 23. Mast-arm mounted lane-use control signs

B. Advance Signs and Markings

The consistent posting of lane-use control signs (*MUTCD* R3 series) 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. [See time-speed-distance table on page 5.] R3-5 and R3-6 series signs should be mounted overhead wherever practical.

References *: *MUTCD*:4

The rationale and supporting evidence for these treatments begins on page 170 of the *Handbook*.

13. Traffic Signals

A. Visibility

To ensure visibility and conspicuity of the traffic signal, the following is recommended:

A-1. A maintained performance level of 200 cd for peak intensity for both 8-in and 12-in signals.
	A-2. Use of 12-in signals in all cases except the few limited situations in which the *MUTCD* allows the use of 8-in signals.References *: *MUTCD*:1

B. All-Red Clearance Interval

To accommodate age differences in perception-reaction time, an all-red clearance interval should be consistently implemented, with length determined according to the Institute of Transportation Engineers (2013) expressions given below:

B-1. Where pedestrian traffic is prohibited, or no pedestrian crossing facilities are provided, use:

	All-red time (r) equals the sum of the width of the intersection (W) in ft and length of the vehicle (L) in feet divided by the quantity of 1.47 times the approach speed of the vehicle (V) in miles per hour.


	B-2. Where pedestrian crossing facilities are provided, use:

	All-red time (r) equals the sum of the width of the intersection (P) in ft and length of the vehicle (L) in feet divided by the quantity of 1.47 times the approach speed of the vehicle (V) in miles per hour.


	where:

	r = length of red clearance interval, to the nearest 0.1 s.
		W = width of intersection (ft), measured from the near-side stop line to the far edge of the conflicting traffic lane along the actual vehicle path.
		P = width of intersection (ft), measured from the near-side stop line to the far side of the farthest conflicting pedestrian crosswalk along the actual vehicle path.
		L = length of vehicle (recommended as 20 ft)
		V = approach speed of the vehicle (mph)References *: *MUTCD*:2

C. Backplates

Backplates with retroreflective borders should be considered as part of efforts to systemically improve safety performance at signalized intersections. Use backplates with traffic signals on all roads with operating speeds of 40 mph or higher. The use of backplates with signals is also recommended on roads with operating speeds lower than 40 mph where engineering judgment indicates a need due to the potential for sun glare problems, site history, or other variables. Yellow retroreflective borders, shown in Figure 24, may be used as an option to improve visibility of the illuminated face of the signal. The yellow retroreflective strip should have a minimum width of 1 inch and a maximum width of 3 inches and be placed along the perimeter of the face of a signal backplate to project a rectangular appearance at night. The yellow retroreflective strip should have a minimum width of 1 inch and a maximum width of 3 inches and be placed along the perimeter of the face of a signal backplate to project a rectangular appearance at night.

References *: *MUTCD*:4



Figure 24. A picture of two traffic signal heads mounted on a mast arm.  Both signal heads have a yellow retroreflective strip around their outer borders.  To the right of both signal heads is a through-only Mandatory Movement Lane Control (R3-5a) sign; a symbolic no-left-turn (R3-2) sign is next to the signal head on the left.




Figure 24. Yellow retroreflective backplates

The rationale and supporting evidence for these treatments begins on page 173 of the *Handbook*.

14. Intersection Lighting

A. Fixed Installations

Wherever feasible, fixed lighting installations are recommended as follows:

A-1. Where the potential for wrong-way movements is indicated through crash experience or engineering judgment.
	A-2. Where twilight or nighttime pedestrian volumes are high.
	A-3. Where shifting lane alignment, turn-only lane assignment, or a pavement-width transition forces a path-following adjustment at or near the intersection.References *: *Green Book*:4, RLH:4

B. Maintenance

Regular cleaning of lamp lenses, and lamp replacement when output has degraded by 20 percent or more of peak performance (based on hours of service and manufacturer's specifications), are recommended for all fixed lighting installations at intersections.

References *: RLH:4

The rationale and supporting evidence for these treatments begins on page 181 of the *Handbook*.

15. Pedestrian Crossings

A. Walking Speed

To accommodate the aging pedestrian who typically has a shorter stride, slower gait, and delayed 'start-up" time before leaving from a position further back from the curb at signalized crossings, the joint application of the following practices is recommended:

A-1. Use a walking speed of 3.0 ft/s to calculate total crossing time (WALK interval plus pedestrian clearance interval).
	A-2. Measure crossing distance from a location 6 ft back from the curb or travel lane edge to the far side of the travel way being crossed.References *: *Green Book*:2, NCHRP 279:2, *MUTCD*:1

B. Channelized Right-Turn Lane

For pedestrian crossings where the right-turn lane is channelized, it is recommended that:

B-1. An adjacent pedestrian refuge island conforming to *MUTCD* (2009) and AASHTO (2011) specifications be provided.
	B-2. If a crosswalk is within the channelized area, it should be located approximately one car length from the yield line for the intersection (see Figure 25), which will allow drivers on the approach leg to look for and yield to pedestrians before reaching the intersecting roadway and scanning for gaps in traffic.References *: *Green Book*:4, NCHRP 279:4, TEH:4, *MUTCD*:2



Figure 25. An image showing an overhead view of an approach to a hypothetical intersection with a channelized right-turn lane.  The channelized right-turn lane shows recommended placement of crosswalk markings and yield line markings, with the notation that the distance between the crosswalk and yield markings should be a minimum of 20 ft.




Figure 25. Pedestrian crossing at channelized right-turn lane

C. Educational Signs

Where engineering judgment deems there to be a need to improve understanding of pedestrian signals, it is recommended that educational signs be posted near the crosswalk as follows:

C-1. For single stage crossings, use *MUTCD* R10-3b, R10-3c, R10-3e, R10-3f, R10-3g, or R10-3i as shown in Figure 26.
	C-2. For two-stage crossings using a median refuge island, use *MUTCD* R10-3d or R10-3h (see Figure 26) on the corners of the intersection and the placards defined above on the median refuge island.References *: *MUTCD*: 2



Figure 26. An image showing eight of the variations of the MUTCD R10-3 series educational plaque for a pedestrian pushbutton.  The image has two rows of four signs each; the top row shows (from left to right) the R10-3b through R10-3e signs, and the bottom row shows (from left to right) the R10-3f through R10-3i signs.




Figure 26. (*MUTCD* R10-3 Series)

D. Turning Vehicles Yield to Pedestrians Sign

The posting of the *MUTCD* R10-15 sign (see Figure 27) is recommended wherever engineering judgment indicates a clear potential for right-turning vehicles to come into conflict with crossing pedestrians.

References *: *MUTCD*:1



Figure 27. An image of a four-leg intersection that shows the recommended placement of the MUTCD R10-15 sign adjacent to the curb radius for right-turning vehicles.




Figure 27. Recommended placement of MUTCD R10-15 sign

E. Leading Pedestrian Interval

At intersections with high turning-vehicle volumes and no turn on red (NTOR) control for traffic moving parallel to a marked crosswalk, a leading pedestrian interval (LPI), timed to allow slower walkers to cross at least one moving lane of traffic is recommended to reduce conflicts between pedestrians and turning vehicles. The length of the LPI, which should be at least 3 s, may be calculated using the formula:

Leading pedestrian interval (LPI) equals the sum of the width of the moving lane (ML) in feet plus the width of the parking lane (PL) in feet plus 6.0, that sum divided by 3.0.


where:

LPI = seconds between onset of the WALK signal for pedestrians and the green indicator for vehicles.
	ML = width of moving lane in ft
	PL = width of parking lane (if any) in ft
	6.0 = distance in ft back from the edge of the curb to the assumed starting location for pedestrians
	3.0 = walking speed in ft/sReferences *: *MUTCD*:1

F. Countdown Signal

Countdown pedestrian signals (see Figure 28) should be installed at all signalized intersections where pedestrian signals are warranted. The 2009 *MUTCD* requires the use of countdown pedestrian signals when the pedestrian change interval is greater than 7s.

References *: *MUTCD*: 1

Figure 28. A picture of a countdown pedestrian signal; the signal displays an orange upraised hand and the number 11.


Figure 28. Countdown pedestrian signal

The rationale and supporting evidence for these treatments begins on page 185 of the *Handbook*.

16. Roundabouts

There are features of roundabout intersections that can benefit aging drivers and be a beneficial treatment over a traditional stop- or signal-controlled intersection if properly designed to meet the needs of that location. When properly designed, roundabouts are low-speed intersections, which provide benefits to aging drivers and pedestrians alike. In addition, roundabouts effectively eliminate severe right-angle crashes. Any crashes that do occur are typically low-angle (i.e., sideswipe) crashes at reduced speeds. The low-speed features associated with roundabouts eliminate the problems associated with making unprotected left turns at intersections. It is therefore recommended that roundabouts be considered as part of the engineering study in the design of new intersections and the redesign of existing intersections.

Treatments for preferred practices when a State or local highway authority has determined through engineering study to install a modern roundabout during construction or reconstruction of an intersection include the following (see Figure 29):



Figure 29. An image of a four-leg single-lane roundabout that shows key dimensions and geometric design elements, as well as the recommended placement of selected signs and pavement markings.




Figure 29. Key geometric design elements and traffic control devices for roundabouts

A. Number of Lanes

Unless required by operational needs, it is recommended that roundabout installations be limited to one-lane entrances and exits and one lane of circulating traffic.

References *: NCHRP 672:1

B. Pedestrian Crossings

Pedestrian crossings at single-lane roundabouts should be set back a minimum of 25 ft from the yield lines and include a crossing island of at least 6 ft in width.

References *: NCHRP 672:1

C. Splitter Islands

To control for wrong-way movements, calm traffic, and provide a pedestrian refuge for all roundabout categories, raised splitter islands should be used, as opposed to pavement markings, to delineate the channelization. The pedestrian crosswalk area should be designed at street level (crosswalk cut through a splitter island).

References *: NCHRP 672:1

D. Conspicuity

To enhance the conspicuity of roundabouts in all categories, the sides and tops of curbs on the splitter islands and the central island should be treated with retroreflective markings, and be maintained at a minimum luminance contrast level* as follows:

D-1. At roundabouts with overhead lighting, a contrast of 2.0 or higher.
	D-2. At roundabouts without overhead lighting, a contrast of 3.0 or higher.Contrast should be calculated according to this formula:

Luminance contrast (C) equals the difference between the luminance of the stripe and the luminance of the pavement divided by the luminance of the pavement.


* Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often described as brightness)—especially at night—this may vary greatly for the same object or marking depending upon such factors as the location and intensity of the source of illumination, and the angle at which a driver views it.

References *: NCHRP 672:4

E. Advance Warning Sign

The use of an advance roundabout warning sign (W2-6), as shown in Figure 30, is recommended on all approaches to a roundabout.

References *: *MUTCD*:1

Figure 30. An image of a symbolic advance roundabout warning (MUTCD W2-6) sign.


Figure 30. (*MUTCD* W2-6)

F. Directional Signs

The use of a Roundabout Directional Arrow sign (R6-4 series) is recommended to direct traffic counter-clockwise around the central island. This sign display should be placed on the central island in direct view of a driver's entry point, as shown in Figure 31, (if different than at the centerline of the approaching roadway).

References *: *MUTCD*:1



Figure 31. An image of a four-leg single-lane roundabout showing the recommended placement of the Roundabout Direction Arrow (R6-4a) sign on one approach.




Figure 31. Roundabout directional arrow sign

G. Roundabout Circulation Plaque

The Roundabout Circulation Plaque (R6-5P) should be placed immediately below the R1-2 Yield sign on both sides of the road at each entrance to a roundabout (see Figure 32).

References *: *MUTCD*:5



Figure 32. An image of a four-leg single-lane roundabout showing the recommended placement of the Yield (R1-2) and Roundabout Circulation Plaque (R6-5P) signs on one approach.




Figure 32. Placement of Roundabout Circulation Plaques

The rationale and supporting evidence for these treatments begins on page 197 of the *Handbook*.

Promising Practices

These are treatments being utilized by transportation agencies that should benefit aging road users as determined by a subjective assessment by staff participating on the development of this *Handbook*. Current trends indicate these practices have a positive impact on aging road user safety.

17. Right-Turn Channelization Design

Right-turn channelization with tighter turning radii to reduce turning speeds to approximately 17 to 18 mph, decrease pedestrian crossing distances, and optimize the right-turning motorists' line of sight should be considered during design, as shown in the Preferred example on the right of Figure 33. Designs such as those on the left of Figure 33 are potentially problematic as drivers have to turn their heads farther to see oncoming traffic. The short curve radius should be between 25 and 40 ft, and the long curve radius should be between 150 and 275 ft. Traffic control devices at the end of the channelization should be visible to vehicles entering the channelized lane.

References *: NCHRP 674:1



Figure 33. An image showing two options for the design of a channelized right-turn lane and the adjacent channelizing island.  The image on the left shows an approach angle of 30 degrees and a head-turning angle for departing drivers of 142 degrees, with the notation of 'High speed, low visibility, head turner' in black text.  The image on the right shows an approach angle of 20 degrees and a head-turning angle for departing drivers of 112 degrees, with the notation of '14-18 mph, good visibility' in black




Figure 33. Right-Turn Channelization Design

The rationale and supporting evidence for these treatments can be found beginning on page 215 of this *Handbook*.

18. Combination Lane-Use/Destination Overhead Guide Signs

At intersections where complex design features or heavy traffic is present, and specific guidance advising roadway users which lane is necessary for their intended destination, combination lane use/destination signs (D15-1) should be used. These signs are typically used as overhead combination lane use destination guide signs and are described in Section 2D.33 of the 2009 *MUTCD* (see Figure 34).

References *: *MUTCD*:1



Figure 34. An image showing two options for the Combination Lane Use/Destination Guide (MUTCD D15-1) sign.  The image on the left shows a green sign with a black and white 'US-56' shield above a modified R3-5 'right turn only' symbol.  The image on the right shows a green sign with the text 'Glenwood Ave' in white above a modified R3-5a 'straight ahead only' symbol.




Figure 34. Combination Lane Use/Destination Guide Sign (*MUTCD* D15-1)

The rationale and supporting evidence for these treatments can be found beginning on page 215 of this *Handbook*.

19. Signal Head Visibility

Place all required signal heads overhead and centered over each lane instead of placing them on pedestal poles (see Figure 35). Supplemental signal heads may be placed on pedestal posts as needed. Do not place a signal head that displays a circular green indication over or directly in front of a left-turn lane. Instead, place a shared signal face over the lane line between the left-turn and through lane, or slightly to the right of it, or place a separate signal face over the center of the left turn lane that uses a flashing yellow arrow as the permissive indication.

References *: *MUTCD*: 1



Figure 35. An image showing the approach to a signalized intersection with a mast arm-mounted signal head above each of the three approach lanes.  The signal heads above the two through lanes show a green ball, and the signal head above the left-turn lane shows an active flashing yellow arrow for permissive left turns.




Figure 35. Example Of One Signal Head Per Lane

The rationale and supporting evidence for these treatments can be found beginning on page 216 of this *Handbook*.

20. High-Visibility Crosswalks

To allow drivers to more easily see pedestrians in a marked crosswalk, high-visibility crosswalk marking patterns should be utilized. Two examples of such markings include white diagonal lines at a 45 degree angle to the crosswalk or the "ladder" crosswalk design shown in Figure 36.

References *: *MUTCD*: 1



Figure 36. An image showing a ladder-style crosswalk on a two-lane street with on-street parking lanes in a shopping district at night.




Figure 36. High-Visibility ("Ladder") Crosswalk

The rationale and supporting evidence for these treatments can be found beginning on page 216 of this *Handbook*.

21. Supplemental Pavement Marking for Stop and Yield Signs

Utilize "STOP AHEAD" word pavement markings to supplement stop ahead signs (W3-1) and "YIELD AHEAD" word pavement markings or yield ahead triangle symbol pavement markings to supplement yield ahead signs (W3-2). See Section 3B.20 of the 2009 *MUTCD* and Figure 37.

References *: *MUTCD*: 1



Figure 37. An image showing two options for yield ahead triangle symbol pavement markings.  The image on the left shows an example for roadways with speed limits of 45 mph or greater; the triangle measures 20 ft in the longitudinal direction by 6 ft in the transverse direction.  The image on the right shows an example for roadways with speed limits of less than 45 mph; the triangle measures 13 ft in the longitudinal direction by 6 ft in the transverse direction.  The stroke width for the long sides of the t




Figure 37. Yield Ahead Triangle Symbols

The rationale and supporting evidence for these treatments can be found beginning on page 217 of this *Handbook*.

22. Reduced Left-Turn-Conflict Intersections

A class of innovative intersection designs accommodate left-turns in unique ways, which greatly reduce, if not eliminate, unprotected left-turns at the intersection. Designs such as the median U-turn intersection (see Figure 38) and restrictedcrossing U-turn (RCUT) intersection (see Figure 39) have features that minimize the operational delay and potential for crashes due to left turns. Other intersection designs that are increasingly common include the displaced left-turn (DLT) intersection and the diverging diamond interchange (DDI). These innovative intersection designs should be considered for suitability during the engineering study for new and reconstructed intersections.



Figure 38. An image showing the configuration of a median U-turn intersection, including vehicle paths and potential conflict points for crossing, merging, and diverging.




Figure 38. Diagram of Median U-Turn Intersection



Figure 39. An image showing the configuration of a restricted crossing U-turn intersection, including vehicle paths and potential conflict points for crossing, merging, and diverging.




Figure 39. Diagram of Restricted Crossing U-Turn Intersection

The rationale and supporting evidence for these treatments can be found beginning on page 218 of this *Handbook*.

23. Accessible Pedestrian Signal (APS) Treatments

A. Pushbutton-Activated Extended Pedestrian Crossing Phase

At crosswalks frequently used by aging pedestrians, consider inclusion of pushbutton-activated extension of the pedestrian crossing phase, using the required signage described by the MUTCD, as shown in Figure 40.

Figure 40. An image of a 'PUSH BUTTON FOR 2 SECONDS FOR EXTRA CROSSING TIME' (MUTCD R10-32P) sign.


Figure 40. (MUTCD R10-32P)

B. Passive Pedestrian Detection

Use of passive pedestrian detection to help aging pedestrians who have difficulty using the pushbutton or to detect pedestrians within the crosswalk that may need more time to complete the crossing maneuver. Passive pedestrian detection uses sensors to detect the presence of pedestrians and register a pedestrian call with the signal system; as a result, the pedestrian does not have to push a button to request a WALK signal or extended crossing time.

The rationale and supporting evidence for these treatments can be found beginning on page 219 of this *Handbook*.

24. Flashing Yellow Arrow

The flashing yellow arrow (see Figure 41) is the recommended signal indication for permissive left-turn movements at signalized intersections.



Figure 41. An image showing four options for a flashing yellow arrow left-turn signal head.  The two options on the left of the figure are side-by-side and show vertical signal heads; the two options on the right of the figure are top-and-bottom and show horizontal signal heads.  The left vertical head and the top horizontal head have four lenses and show left arrows in the following order: red, yellow, flashing yellow, green.  The right vertical head and the bottom horizontal head have three lenses and sho




Figure 41. Typical arrangements of signal faces with flashing yellow arrow indications for permissive left-turn movements

The rationale and supporting evidence for these treatments begins on page 220 of the *Handbook*.

References Legend

*See pages 3 and 4 for full description of codes and acronyms of cited design guides.*

1: most conservative
	2: preferred among differing guides
	3: new application of current practice
	4: more specific, detailed or stringent
	5: permissible only in accordance with MUTCD section 1A.10, Interpretations, Experimentations, and Changes
      
  Book traversal links for Chapter 2. Intersections
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                    Chapter 3. Interchanges ›
                
                Book:Handbook for Designing Roadways for the Aging Population
              Preface
                Acknowledgements
                Abbreviations and Acronyms
                Chapter 1. How to Use this Handbook
                Part I. Treatments
                Chapter 2. Intersections
                Chapter 3. Interchanges
                Chapter 4. Roadway Segments
                Chapter 5. Construction/Work Zones
                Chapter 6. Highway-Rail Grade Crossing
                Part II. Rationale and Supporting Evidence
                Chapter 7. Intersections
                Chapter 8. Interchanges
                Chapter 9. Roadway Segments
                Chapter 10. Construction/Work Zones
                Chapter 11. Highway-Rail Grade Crossings
                APPENDIX A
                APPENDIX B
                APPENDIX C
                APPENDIX D U.S. DEPARTMENT OF TRANSPORTATION

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