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Many thanks to the Washington Department of Transportation for providing the data for this analysis and for their thoughtful comments in the preparation of this paper. Slide 3
Generally, the goal of roadside design is to minimize, in so far as practical, the chance of fatal or incapacitating injury crashes on the roadside. Slide 4
applicable to new construction or major reconstruction projects. concepts cannot, and should not, be included in their totality on every single project. Slide 5
How much can risk be minimize while maintaining agreements for access with utility companies? This study developed a quantitative approach for measuring the risk of different pole location alternatives such that poles can be located where the greatest risk reduction can be realized. Slide 6
Benefit-cost methods have been used in roadside safety for over 40 years. Benefit-cost methods compare the risk reduction to the capital cost increase for each viable alternative. Issue: the risk reduction benefits and direct improvement costs do not accrue to the same entities. Slide 7
Separate the risk assessment from the benefit-cost assessment. Consider of risk reduction across alternatives. Cost-benefit and risk assessment tools are readily available in RSAPv3. Slide 8
Slide 9 Image source: https://www.google.com/imgres?im gurl=https%3a%2f%2fupload.wik imedia.org%2fwikipedia%2fcom mons%2fthumb%2f1%2f12%2f Dice_Distribution_%2528bar%252 9.svg%2F250px- Dice_Distribution_%2528bar%252 9.svg.png&imgrefurl=https%3A%2 F%2Fen.wikipedia.org%2Fwiki%2 FProbability_distribution&docid=Dl K1zbnmD2cMHM&tbnid=OOUB0B v408twcm%3a&vet=10ahukewj 8rumbiYnUAhVHzoMKHXp2DCU4 ZBAzCAcoBTAF..i&w=250&h=188 &bih=638&biw=1360&q=probabilit y&ved=0ahukewj8rumbiynuahv HzoMKHXp2DCU4ZBAzCAcoBTA F&iact=mrc&uact=8
Enc/Mi/Year/EDGE For a roadside, the probability of observing a crash can be found using RSAPv3. The number of trials is equal to the number of encroachments. 2.0 1.5 1.0 0.5 0.0 0 10000 20000 30000 40000 50000 Bi-directional AADT (vpd) Slide 10
An undivided roadway with a posted speed limit of 45 mph and 10% heavy vehicles was considered. The design alternatives considered were as follows: Slide 11
137 11 20 30 Slide 12
200 11 20 30 Slide 13
274 Slide 14 11 20 30
Enc./Edge-mile/Year 5 4 3 2 1 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 A+K Risk Slide 15 Offsets: 11' 20' 30' 137' 137' 137' 200' 200' 200' 274' 274' 274'
Slide 16
Dead on Arrival Dead at Scene Died in Hospital Serious Injury Total A+K City 5 55 32 404 496 County 12 132 49 600 793 State 5 57 21 206 289 Misc. way 0 0 0 5 5 Total 22 244 102 1215 1583 Crashes/yr 1.57 17.43 7.29 86.79 113.07 Slide 17
Evident Injury Possible Injury No Injury Unk Total BCO City 1802 2035 6805 1482 12,124 County 2498 2341 7109 1358 13,306 State 875 900 2388 260 4,423 Misc. way 10 4 33 11 58 Total 5185 5280 16335 3111 29,911 Crashes/yr 370.36 377.14 1166.79 222.21 2,136.50 Slide 18
Centerline Miles Jurisdiction One-way Miles Divided Miles Undivided Miles Edge Miles State Highway 36.71 1,401.58 7,012.72 19,705.16 County Highway 1.98 0.00 14,379.94 28,763.83 City Highway 100.30 0.00 4,455.18 9,110.97 Slide 19
K+A Crash Risk/year/edge mile 0.0045 0.0040 0.0035 0.0030 0.0025 0.0020 0.0015 0.0010 0.0005 0.0000 (1/256) (1/500) (1/1000) City County State Jurisdiction Slide 20
Enc./Edge-mile/Year 5 State County City 4 3 2 1 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 A+K Risk Slide 21 Offsets: 11' 20' 30' 137' 137' 137' 200' 200' 200' 274' 274' 274'
Two utility pole crashes per year per mile? One? Zero? Maybe we can agree to reduce the existing risk by, for example, by half? Slide 22
Enc./Edge-mile/Year 5 State County City 4 3 2 1 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 A+K Risk Slide 23 Offsets: 11' 20' 30' 137' 137' 137' 200' 200' 200' 274' 274' 274'
Enc./Edge-mile/Year 5 State County City 4 3 2 1 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 A+K Risk Slide 24 Offsets: 11' 20' 30' 137' 137' 137' 200' 200' 200' 274' 274' 274'
Does a pole at a location create more than what is considered acceptable? Yes locate elsewhere No consider next pole. Slide 25
Example Application 6-degree horizontal curve. 5% downgrade 200 SR 1 Slide 26 11
Enc/Mi/Year/EDGE 2.0 1.8 1.6 1.4 0.93 encroachments/edge-mile/yr 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 10000 20000 30000 40000 50000 Bi-directional AADT (vpd) Slide 27
-115-57 -29-17 -13-10 -6-3 0 3 6 10 13 17 29 57 115 Modification 3.5 3.0 2.5 2.0 f HC =1.5 1.5 1.0 0.5 0.0 Slide 28 Degree of Curve in Primary Direction of Travel
Modification Let s say %G=-5 f VC_PRIM =1.1 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0-14 -12-10 -8-6 -4-2 0 2 4 6 8 10 12 14 Percent Grade in the Primary Direction of Travel Slide 29
0.93 1.1 1.5 = 1.53. On average 1.53 vehicles/edge-mile/year will leave the travelled way on this particular road with its 6 degree horizontal curve and 5% downgrade. Slide 30
Enc./Edge-mile/Year 50% State Risk 2 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1 0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 A+K Risk Slide 31 Offsets: 11' 20' 30' 137' 137' 137' 200' 200' 200' 274' 274' 274'
This example shows that the existing utility pole risk can be quickly compared to the jurisdictional risk goal or site-specific goals. This method also allows the engineer to quickly assess if changing the offset or spacing would reduce the risk to an acceptable level. The primary advantage to this approach is that it allows for utility companies and transportation agencies to target improvements to the neediest areas. Slide 32
Christine E. Carrigan, P.E., PhD Phone: 207 513 6057 christine@roadsafellc.com Malcolm H. Ray, P.E., PhD Phone: 207 514 5474 mac@roadsafellc.com Slide 33