PROJECT:

08CR2: NHS Warning & Delineation Improvements

Description:

Several segments on the Parks, Glenn, Seward and Sterling Highways had a significant number of fatal and major injury crashes during the 2001-2005 study period.  One pattern which emerged when looking at these higher severity crashes was the percentage of them that occurred on either horizontal curves, grades, or both.  Each of the four major NHS rural highways was studied in greater detail looking at crash types, crash severity, roadway surface and ambient lighting conditions, and location of fatal and major injury crashes relative to horizontal and vertical alignment.

Parks Highway
There were a total of 360 crashes with fatalities or injuries on the Parks Highway between MP 42 (Wasilla) and MP 163 (Region Boundary) during the 2001-2005 study period.  119 or nearly 33% were either rear end or right angle accidents.  Head on crashes (46) accounted for 13% and run off the road crashes totaled 146 or approximately 40%.  24 of these resulted in a fatality, 61 resulted in major injury, and 275 resulted in minor injury.  Accident rates on six of the Parks Highway segments were above the statewide average for a rural NHS interstate designated highway.  Alcohol or drugs were a factor in 39 of these crashes.  Over 58% of the fatal crashes and over 54% of the major injury crashes occurred in either horizontal curves, grades or both.

Glenn Highway
There were a total of 202 crashes with fatalities or injuries on the Glenn Highway between MP 44 (Palmer) and MP 118 (Region Boundary) during the 2001-2005 study period.  Nearly 30% were either rear end or right angle accidents.  Head on crashes accounted for 10% and run off the road crashes totaled approximately 46%.  12 of these resulted in a fatality, 43 resulted in major injury, and 147 resulted in minor injury.  Accident rates on two of the Glenn Highway segments were above the statewide average for a rural NHS interstate designated highway.  Alcohol or drugs were a factor in 32 of these crashes.  Over 66% of the fatal crashes and over 65% of the major injury crashes occurred in either horizontal curves, grades or both.

Seward Highway
There were a total of 432 crashes with fatalities or injuries on the Seward Highway between MP 8 (north of Seward) and MP 117 (Potter Marsh) during the 2001-2005 study period.  Nearly 21% were either rear end or right angle accidents.  Head on crashes accounted for 13% and run off the road crashes totaled approximately 41%.  29 of these resulted in a fatality, 93 resulted in major injury, and 310 resulted in minor injury.  Accident rates on two of the Seward Highway segments were above the statewide average for a rural NHS interstate designated highway.  Alcohol or drugs were a factor in 45 of these crashes.  Over 86% of the fatal crashes and over 55% of the major injury crashes occurred in either horizontal curves, grades or both.

Sterling Highway
There were a total of 597 crashes with fatalities or injuries on the Sterling Highway between MP 37 (Seward Highway Jct.) and MP 169 (Homer Hill) during the 2001-2005 study period.   Nearly 32% were either rear end or right angle accidents.  Head on crashes accounted for nearly 9% and run off the road crashes totaled approximately 41%.  26 of these resulted in a fatality, 92 resulted in major injury, and 479 resulted in minor injury.  Accident rates on seven of the Sterling Highway segments were above the statewide average for a rural NHS interstate designated highway.  Alcohol or drugs were a factor in 58 of these crashes.  Nearly 58% of the fatal crashes and over 53% of the major injury crashes occurred in either horizontal curves, grades or both.

Since fatal and major injury crashes are generally scattered along a route, they do not lend themselves to individual mitigation.  Instead, we are proposing a project to mitigate the fatal and major injury crashes occurring on these routes using a corridor approach.  Since we defined a pattern of fatal and major injury run off the road type crashes as well as some head on crashes on horizontal curves and/or grade, we propose the following work:

• Install chevron alignment signs on the sharpest horizontal curves with a demonstrated run-off-the-road crash pattern.

• Install rigid roadside delineators on other horizontal curves where chevron alignment signs have not been designated.

• Install new or improved advance curve warning signs on all horizontal curves where the safe speed is at or below the posted speed limit.

• Install new guardrail at selected locations to prevent fatal and severe injury crashes.

• Delineate existing barriers that presently are not delineated.  An example of this is the concrete barrier on the Glenn Highway in the vicinity of MP 109.

Both shoulder and centerline rumble strips are to be installed along portions of these routes under a separate project.

Several studies have demonstrated that roadside delineators for horizontal curves are generally more effective during hours of darkness.  However, highways with roadside delineators have been shown to be safer than those without them.  The majority of crashes on the four rural NHS routes have occurred during daylight hours.  However, there are a number of horizontal curves where there are no visual queues such as a tree line of cut bank. Therefore, we feel additional curve delineation will be effective even during daylight hours.

Both flexible and rigid roadside delineators have been used in Alaska.  The flexible delineators have not performed well and have generally been destroyed within a few years of their installation.  Therefore, only rigid delineators or guardrail/barrier mounted delineators will be used.  Standard delineator colors, generally white for right side installations, provide poor delineation during daylight hours and during winter months when the surrounding ground is covered with snow.  We propose the use of another color for the delineator post with a white reflector attached.  The typical orange candles used in highway construction work zones are quite effective in delineating roadway alignment changes, especially during daylight hours.  Therefore, we are proposing to use a delineator post that are much more visible during daylight hours and during snow months such as an orange sleeve around the post with a white reflector attached.

This project is scheduled for construction in 2011.

Charlie Wagner, P.E.
Alaska State Department of Transportation and Public Facilities (ADOT&PF)

charles.wagner@alaska.gov