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Publication Number: FHWA-RD-01-103
Date: May 2001

Highway Design Handbook for Older Drivers and Pedestrians

IV. CONSTRUCTION/WORK ZONES

 

Background and Scope of Handbook Recommendations

Highway construction and maintenance zones deserve special consideration with respect to older driver needs because of their strong potential to violate driver expectancy. Alexander and Lunenfeld (1986) properly emphasized that driver expectancy is a key factor affecting the safety and efficiency of all aspects of the driving task. Consequently, it is understandable that crash analyses consistently show that more crashes occur on highway segments containing construction zones than on the same highway segments before the zones were implemented (Juergens, 1972; Graham, Paulsen, and Glennon, 1977; Lisle, 1978; Nemeth and Migletz, 1978; Paulsen, Harwood, and Glennon, 1978; Garber and Woo, 1990; Hawkins, Kacir, and Ogden, 1992).

Work-zone traffic control must provide adequate notice to motorists that describes the condition ahead, the location, and the required driver response. Once drivers reach a work zone, pavement markings, signing, and channelization must be conspicuous and unambiguous in providing guidance through the area. The National Transportation Safety Board (NTSB, 1992) stated that the MUTCD guidelines concerning signing and other work-zone safety features provide more than adequate warning for a vigilant driver, but may be inadequate for an inattentive or otherwise impaired driver. It is within this context that functional deficits associated with normal aging, as described below, may place older drivers at greater risk when negotiating work zones.

In a crash analysis at 20 case-study work-zone locations, among the most frequently listed contributing factors were driver attention errors and failure to yield the right-of-way (Pigman and Agent, 1990). Older drivers are most likely to demonstrate these deficits. Research on selective attention has documented that older adults respond much more slowly to stimuli that are unexpected (Hoyer and Familant, 1987), suggesting that older adults could be particularly disadvantaged by changes in roadway geometry and operations such as those found in construction zones. There is also research indicating that older adults are more likely to respond to new traffic patterns in an "automatized" fashion, resulting in more frequent driver error (Fisk, McGee, and Giambra, 1988). To respond in situations that require decisions among multiple and/or unfamiliar alternatives, with unexpected path-following cues, drivers' actions are described by complex reaction times that are longer than reaction times in simple situations with expected cues. In Mihal and Barrett's analysis (1976) relating simple, choice, and complex reaction time to crash involvement, only an increase in complex reaction time was associated with crashes. The relationship with driver age was most striking: the correlation between complex reaction time and crash involvement increased from r= 0.27 for the total analysis sample (all ages) to r= 0.52 when only older adults were included. Such data suggest that in situations where there is increased complexity in the information to be processed by drivers--such as in work zones--the most relevant information must be communicated in a dramatic manner to ensure that it receives a high priority by older individuals.

Compounding their exaggerated difficulties in allocating attention to the most relevant aspects of novel driving situations, diminished visual capabilities among older drivers are well documented (McFarland, Domey, Warren, and Ward, 1960; Weymouth, 1960; Richards, 1972; Pitts, 1982; Sekuler, Kline, and Dismukes, 1982; Owsley, Sekuler, and Siemsen, 1983; Wood and Troutbeck, 1994). Deficits in static and dynamic acuity and contrast sensitivity, particularly under low-luminance conditions, make it more difficult for them to detect and read traffic signs, to read variable message signs, and to detect pavement markings and downstream channelization devices. Olson (1988) determined that for a traffic sign to be noticed at night in a visually complex environment, its reflectivity must be increased by a factor of 10 to achieve the same level of conspicuity as in a low-complexity environment. Mace (1988) asserted that the minimum required visibility distance--the distance from a traffic sign required by drivers in order to detect the sign, understand the situation, make a decision, and complete a vehicle maneuver before reaching a sign--is increased significantly for older drivers due to their poorer visual acuity and contrast sensitivity, coupled with inadequate sign luminance and legend size. Other age-related deficits cited by Mace (1988) include lowered driver alertness, slower detection time in complex roadway scenes due to distraction from irrelevant stimuli, increased time to understand unclear messages such as symbols, and slower decision making.

In a mail survey of 1,329 American Association of Retired Persons (AARP) members ages 50 to 97, conducted to identify older driver freeway needs and capabilities, 21 percent of the respondents indicated that they have problems with accurately judging distances in construction zones (Knoblauch, Nitzburg, and Seifert, 1997). These drivers reported additional problems in negotiating work zones, including congestion/traffic; lack of adequate warning; narrow lanes; lane closures and lane shifts; and difficulty staying in their lane.

This section will provide recommendations to enhance the performance of diminished-capacity drivers as they approach and travel through construction/work zones, keyed to five specific design elements: A. lane closure/lane transition practices; B. portable changeable (variable) message signing practices; C. channelization practices (path guidance); D. delineation of crossovers/alternate travel paths; and E. temporary pavement markings.

 

Recommendations by Design Element

  A. Design Element: Lane Closure/Lane Transition Practices
MUTCD:4 (1) At construction/maintenance work zones on high-speed roadways (where the posted speed limit is 72 km/h [45 mi/h] or greater) and divided highways, the consistent use of a flashing arrow panel located at the taper for each lane closure is recommended.
ITE:4
MUTCD:4
(2) In implementing advance signing for lane closures as per MUTCD Part 6, it is recommended that:

A supplemental (portable) changeable message sign (CMS) displaying the one-page (phase) message LEFT (RIGHT, CENTER) LANE CLOSED should be placed 800 to 1600 m (2625 to 5250 ft) upstream of the lane closure taper.

or

Redundant static signs should be used, with a minimum letter height of 200 mm (8 in) and fluorescent orange retroreflective sheeting that provides high retroreflectance at the widest available observation angle; where both the first upstream sign (e.g., W20-1) and the second sign (e.g., W20-5) encountered by the driver are equipped with flashing warning lights throughout the entire time period of the lane closure.

The rationale and supporting evidence for these recommendations

 

  B. Design Element: Portable Changeable (Variable) Message Signing Practices
ITE:2
MUTCD:4
(1) It is recommended that no more than two phases be used on a changeable message sign (CMS); if a message cannot be conveyed in two phases, multiple CMS's and/or a supplemental highway advisory radio message should be used.
MUTCD:4 (2) It is recommended that each phase of a CMS message be displayed for a minimum of 3 s.
MUTCD:4 (3) It is recommended that no more than one unit of information be displayed on a single line on a CMS, and no more than three units should be displayed for any single phase. A unit of information is one or more words that answers a specific question (e.g., What happened? Where? What is the effect on traffic? What should the driver do?).
ITE:4
MUTCD:4
(4) For CMS messages split into two phases, a total of no more than four unique units of information should be presented.
ITE:4
MUTCD:4
(5) When a portable CMS is used to display a message in two phases, the problem and location statements should be displayed during phase 1 and the effect or action statement during phase 2. For example:

 

Phase 1
Roadwork 2 Miles Ahead sign
Phase 2
Left Lane Closed sign

If legibility distance restrictions rule out a two-phase display, the use of abbreviations [as specified in the MUTCD (FHWA, 2000)] plus elimination of the problem statement is the recommended strategy to allow for the presentation of the entire message in one phase:

Left Lane Closed in 2 MI sign
MUTCD:4 (6) For superior legibility, it is recommended that:

(6a) Only single-stroke fonts should be used for displays of alphanumeric characters on portable CMS's with the conventional 5- x 7-pixel matrix; double-stroke fonts should be avoided.

MUTCD:4

 

(6b) As new portable CMS's are procured by a highway agency, the performance specifications of such devices should include a minimum character width-to-height ratio of 0.7 (complete character) and a maximum stroke width-to-height ratio of 0.13.

The rationale and supporting evidence for these recommendations

 

  C. Design Element: Channelization Practices (Path Guidance)
MUTCD:4 (1)The following minimum dimensions or properties for channelizing devices used in highway work zones are recommended to accommodate the needs of older drivers:

(1a)Traffic cones--900 mm (36 in) high, with two bands of retroreflective material totaling at least 300-mm- [12-in-] wide for nighttime operations.

MUTCD:4

(1b) Tubular markers--1050 mm (42 in) high, with a single band of retroreflective material at least 300-mm- [12-in-] wide for nighttime operations.

MUTCD:1

(1c) Vertical (striped) panels--300 mm (12 in) wide.

MUTCD:4

(1d) Chevron panels (W1-8) modified in color to be used in a work zone (white on orange)--450 mm (18 in) wide and 600 mm (24 in) high.

MUTCD:2

(1e) Barricades--300-mm x 900-mm (12-in x 36-in) minimum dimension.

MUTCD:4

(1f) Drums--450 mm x 900 mm (18 in x 36 in), with high-brightness sheeting for the orange and white retroreflective stripes (as per MUTCD guidelines).

MUTCD:4 (2) It is recommended that channelizing devices through work zones (in non-crossover applications) be spaced at no more than a distance in feet equal to the speed limit through the work zone in miles per hour (e.g., in 40-mi/h work zone, channelizing devices should be spaced at no farther apart than 40 ft). Where engineering judgment indicates a special need for speed reduction where there is horizontal curvature or through the taper for a lane closure, spacing of channelizing devices at a distance in feet equal to no more than half of the speed limit in miles per hour is recommended (e.g., in a 40-mi/h zone, space the devices no farther apart than 20 ft).
MUTCD:4

(3) The use of side reflectors with cube-corner lenses or reflectors (facing the driver) mounted on top of concrete safety-shaped barriers and related temporary channelizing barriers is recommended, spaced (in feet) at not more than the construction zone speed limit (in miles per hour) through a work zone.

 

The rationale and supporting evidence for this recommendation

 

  D. Design Element: Delineation of Crossovers/Alternate Travel Paths
MUTCD:1 (1)The use of positive barriers in transition zones and positive separation (channelization) between opposing two-lane traffic throughout a crossover is recommended, for intermediate- and long-term-duration work zones, for all roadway classes except residential.
MUTCD:4 (2)A minimum spacing (in feet) of one-half the construction zone speed limit (in miles per hour) for channelizing devices (other than concrete barriers) is recommended in transition areas, and through the length of the crossover, and in the termination area downstream (where operations as existed prior to the crossover resume).
MUTCD:4 (3) The use of side reflectors with cube-corner lenses spaced (in feet) at not more than the construction zone speed limit (in miles per hour) on concrete channelizing barriers in crossovers (or alternately the use of retroreflective sheeting on plastic glare-control louvers [paddles] placed in crossovers) is recommended.
MUTCD:4

(4)It is recommended for construction/work zones on high-volume roadways that plastic glare-control louvers (paddles) be mounted on top of concrete channelizing barriers, when used in transition and crossover areas, at a spacing of not more than 600 mm (24 in).

 

The rationale and supporting evidence for these recommendations

 

  E. Design Element: Temporary Pavement Markings
MUTCD:2 (1)Where temporary pavement markings shorter than the 3-m (10-ft) tandard length are implemented, it is recommended that a raised pavement marker be placed at the center of the gap between successive markings.

 

The rationale and supporting evidence for this recommendation

 

FHWA-RD-01-103

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