SLIDE 1 NCHRP 633 Impact of Shoulder Width and Median Width on Safety
Unive rsity o f K e ntuc ky
K T C Pa rtne ring Co nfe re nc e Aug ust 2010
SLIDE 2 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
SLIDE 3 Background
(2/2)
Pro je c t issue s
Uniq ue ne ss Co nte xt
Sa fe ty implic a tio ns
SLIDE 4
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
SLIDE 5
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
SLIDE 6 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
SLIDE 7 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
SLIDE 8 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)
SLIDE 9
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%
SLIDE 10 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
SLIDE 11 Methodology
(1/5)
All crashes Divided Undivided Single Multi All Same for Injury only crashes
SLIDE 12 Methodology
(2/5)
Ne g a tive b ino mia l
E [N] = L e b 0+b 1 lnADT
+ b 2X2+b 3X3+…+b nXn
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
SLIDE 13 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
SLIDE 14 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 AMF
= e b i
b i = 0.407 the n AMF
= e 0.407 =1.50
SLIDE 15 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
SLIDE 16 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
SLIDE 17 Shoulder Width AMF
Ca te g o ry Ave ra g e sho ulde r width (ft) 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
SLIDE 18 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
Me dia n b a rrie r pre se nc e
SLIDE 19 Median Width AMF
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
Ca te g o ry Me dia n width (ft) 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
SLIDE 20 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
SLIDE 21 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
SLIDE 22
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
SLIDE 23 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
SLIDE 24 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
SLIDE 25 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
