NCHRP 633 Impact of Shoulder Width and Median Width on Safety N. - PowerPoint PPT Presentation

NCHRP 633 Impact of Shoulder Width and Median Width on Safety N. Sta ma tia dis Unive rsity o f K e ntuc ky K T C Pa rtne ring Co nfe re nc e Aug ust 2010

Background (1/2)  Ob je c tive s o f ro a dwa y de sig ns  Sa fe ty  E ffic ie nc y  Huma n a nd na tura l e nviro nme nt fit  Ne e d to e va lua te a lte rna tive s  T ra de o ff g e o me tric e le me nts  Guide line s vs. sta nda rds

Background (2/2)  Pro je c t issue s  Uniq ue ne ss  Co nte xt  Sa fe ty implic a tio ns

Research Objectives  Unde rsta nd re la tio nships a nd q ua ntify tra de o ffs fo r de sig n e le me nts  De ve lo p info rma tio n re so urc e s a nd de c isio n to o ls fo r de sig ne rs

Study Approach  L ite ra ture re vie w  Da ta a c q uisitio n a nd a na lysis  Mo de l de ve lo pme nt a nd e va lua tio n  Guide line de ve lo pme nt  F ina l re po rt

Research Focus  Multi-la ne rura l ro a ds  Da ta o f inte re st  L a ne width  Sho ulde r width a nd type  Me dia n width a nd type  Cle a r zo ne

Literature Review  Sa fe ty implic a tio ns fro m de sig n e le me nt tra de o ffs  No t muc h o n multi-la ne rura l ro a ds  Hig hwa y Sa fe ty Ma nua l AMF va lue s  2 la ne rura l ro a ds

Data  Da ta fo r MN, CA, K Y  1991-2002 pe rio d  Da ta o f inte re st  L a ne width  Sho ulde r width a nd type  Me dia n width a nd type  Cle a r zo ne (K Y o nly)

Data Distribution Va ria b le CA MN K Y L e ng th (mi) 835.84 975.16 576.08 Se g me nts 2,726 4,385 930 Numb e r o f c ra she s 30,413 16,244 30,788 Numb e r o f injury c ra she s 7,676 2,173 10,428 Se g me nts with no c ra she s 68% 80% 63%

Data Issues  Da ta issue s  Princ . Arte ria l  4 la ne s  12-ft la ne s  8-ft sho ulde rs  Guide line s fo r 4-la ne rura l ro a ds with 12-fo o t la ne s

Methodology (1/5) All crashes Divided Undivided Single Multi All Same for Injury only crashes

Methodology (2/5)  Ne g a tive b ino mia l e b 0+b 1 lnADT + b 2X2+b 3X3+…+b nXn E [N] = L whe re E [N] numb e r o f c ra she s pe r ye a r L se g me nt le ng th ADT a ve ra g e da ily tra ffic Xi e xpla na to ry va ria b le s

Methodology (3/5)  Va ria b le s c o nside re d  F unc tio na l c la ss  Rig ht sho ulde r pa ve d  L e ft turn la ne pre se nc e  Me dia n b a rrie r pre se nc e  Sho ulde r width  Me dia n width

Methodology (4/5)  Ac c ide nt Mo dific a tio n F a c to rs (AMF )  Use c o e ffic ie nts = e b i  AMF = e 0.407 =1.50  b i = 0.407 the n AMF

Methodology (5/5)  Guide line s  Re vie w NCHRP 633 mo de ls  Appra ise c urre nt kno wle dg e  Co nsult HSM mo de ls  Use e xpe rt pa ne l re vie w  Re c o mme nd AMF

Shoulder Width  Width impa c ts c ra she s  Po sitive e ffe c t  Wide r sho ulde rs re duc e c ra she s  Wide r sho ulde rs e nc o ura g e hig he r spe e ds  I nte ra c tio n with la ne width a nd numb e r o f la ne s

Shoulder Width AMF Ave ra g e sho ulde r width (ft) Ca te g o ry 0 3 4 5 6 7 8 Undivide d 1.22 1.00 0.94 0.87 0.82 0.76 0.71 Divide d 1.17 1.00 0.95 0.9 0.85 0.81 0.77 No te s: AMF fo r a ll c ra she s a nd se ve ritie s Divide d: L e ft a nd rig ht sho ulde r widths Undivide d: Rig ht sho ulde rs widths

Medians  Me dia n e ffe c t  Cro ss me dia n c ra she s  Me dia n re la te d c ra she s  T o ta l e ffe c t unkno wn  Me dia n b a rrie r pre se nc e

Median Width AMF Me dia n width (ft) Ca te g o ry 10 20 30 40 50 60 70 80 Multi-ve hic le 1.00 0.91 0.83 0.75 0.68 0.62 0.57 0.51 No te s: AMF fo r a ll se ve ritie s No e ffe c t o n sing le ve hic le c ra she s

Median Barrier  I mpa c t o n c ra she s unkno wn  I nc re a se due to pre se nc e  De c re a se o n se ve rity  Me dia n b a rrie r type  Me dia n b a rrie r pla c e me nt  Da ta a nd mo de ls inc o nc lusive

Application  AMF e stima te c ho ic e impa c t  Sing le e le me nt   N = [AMF i / AMF j ] – 1  Multiple e le me nts  AMF i x AMF j

Application Example Wide n sho ulde r fro m 4 to 8 ft o n a fo ur la ne undivide d ro a d AMF 4 = 0.71; AMF 8 = 0.94  N = (0.71/ 0.94)-1 = -0.24 24% c ra sh re duc tio n pe r ye a r pe r mile

NCHRP 633 vs. HSM (1/2)  Sho ulde r width  Simila r tre nds  Divide d: Sa me ma g nitude  Undivide d: L a rg e r diffe re nc e s  No AMF fo r sho ulde rs o ve r 8 fe e t  HSM sho ulde r re la te d c ra she s o nly

NCHRP 633 vs. HSM (2/2)  Me dia n width  Simila r tre nds  HSM sma lle r re duc tio ns  HSM me dia n re la te d o nly c ra she s a nd b a rrie r pre se nt

Conclusions  AMF c a n b e use d fo r a ll c ra she s  All fo r 4-la ne rura l ro a ds with 12- ft la ne s  Suppo rtive o f HSM  Additio na l wo rk o n me dia n b a rrie r  T ype a nd pla c e me nt  Cra sh type s a nd se ve rity