preliminary analysis of speed limit changes on oregon ......• safety analysis is preliminary •...
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Preliminary Analysis of Speed Limit Changes in Eastern Oregon
Chris Monsere, Ph.D., P.E.Professor and ChairDepartment of Civil and Environmental EngineeringPortland State University
Oregon Transportation Commission Meeting1/17/2019
1
Method
Control65 mph segments
• 151 miles• 5 speed stations• I-5 and I-84 freeway
55 mph segments• 539 miles• 10 speed stations• Some in Eastern
Oregon, others in Valley/Coast
Increased Posted Speed65 → 70 mph segments
• 417 miles• 6 speed stations• I-84, I-82 and US-395
(a 2- lane segment)
55 → 65 mph segments• 1,009 miles• 11 speed stations• Mostly 2-lane
segments in Eastern Oregon
Compare changes in speed and safety on segments with increased speed limits to control locations.
2
3
1
9
11
6
5
12
2
37
8
Control Segments
10
4
4
Speed Comparisons
• Source • Automatic Traffic Recorders (ATR) – all vehicles by month• HERENow, as proof of concept
• Comparison Periods• Data from January 2015 to March 2018• May to October months only (without snow/ice)• December to February months only (winter months)
• Measures (all vehicles, by month)• Estimated average speed• Percent of vehicles exceeding 65 mph, 75 mph and 85 mph
• Statistical Tests• T-test of means (unequal variance)• Paired t-test of means (2015 to 2018)
5
55
60
65
70
75Es
timat
ed A
vera
ge S
peed
(mph
)Average Speed, Control Segments (65 mph)
55
60
65
70
75
Jan
15Fe
b 15
Mar
15
Apr 1
5M
ay 1
5Ju
n 15
Jul 1
5Au
g 15
Sep
15O
ct 1
5N
ov 1
5D
ec 1
5Ja
n 16
Feb
16M
ar 1
6Ap
r 16
May
16
Jun
16Ju
l 16
Aug
16Se
p 16
Oct
16
Nov
16
Dec
16
Jan
17Fe
b 17
Mar
17
Apr 1
7M
ay 1
7Ju
n 17
Jul 1
7Au
g 17
Sep
17O
ct 1
7N
ov 1
7D
ec 1
7Ja
n 18
Feb
18M
ar 1
8
Estim
ated
Ave
rage
Spe
ed (m
ph) Average Speed, Increased Speed Segments (65 to 70 mph)
6
40
45
50
55
60
65
70
Jan
15Fe
b 15
Mar
15
Apr 1
5M
ay 1
5Ju
n 15
Jul 1
5Au
g 15
Sep
15O
ct 1
5N
ov 1
5D
ec 1
5Ja
n 16
Feb
16M
ar 1
6Ap
r 16
May
16
Jun
16Ju
l 16
Aug
16Se
p 16
Oct
16
Nov
16
Dec
16
Jan
17Fe
b 17
Mar
17
Apr 1
7M
ay 1
7Ju
n 17
Jul 1
7Au
g 17
Sep
17O
ct 1
7N
ov 1
7D
ec 1
7Ja
n 18
Feb
18M
ar 1
8Estim
ated
Ave
rage
Spe
ed (m
ph) Average Speed, Increased Speed Segments (55 to 65 mph)
40
45
50
55
60
65
70
Estim
ated
Ave
rage
Spe
ed (m
ph)
Average Speed, Control Segments (55 mph)
7
Change in Average Speed Change (mph)
0.1
3.0
0.1
2.6
Control (65 mph)
Speed Change (70 mph)
Control (55 mph)
Speed Change (65 mph)
8
67.0 mph before, 69.9 mph after
55.9 mph before, 58.5 mph after
Change in Percent Exceeding
1.7
12.0
0.2
1.9
Control (65 mph)
Speed Change (70mph)
Control (55 mph)
Speed Change (65mph)
Percent of Vehicles > 75 mph
0.0
0.9
0.1
0.3
Control (65 mph)
Speed Change (70 mph)
Control (55 mph)
Speed Change (65 mph)
Percent of Vehicles > 85 mph
9
11.5% before, 23.5% after
1.5% before, 3.3% after
0.8% before, 1.8% after
0.1% before, 0.4% after
Crash Comparisons
• Measures• All vehicle traffic volume• All vehicles: 1) Total crashes 2) Fatal + Injury A crashes• Truck-involved: 1) Total crashes 2) Fatal + Injury A crashes• Proportions by Crash Types
• Comparison Periods• Data from March 2013 to February 2017• Year is March to February• March to October
• Index ( > 1.0 is increase in crashes)• Index = 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑖𝑖𝑖𝑖 𝑡𝑡𝐶𝐶𝐶 𝑝𝑝𝑝𝑝𝐶𝐶𝑡𝑡 1 𝑦𝑦𝐶𝐶𝐶𝐶𝐶𝐶 𝑝𝑝𝐶𝐶𝐶𝐶𝑖𝑖𝑝𝑝𝑝𝑝
𝐴𝐴𝐴𝐴𝐶𝐶𝐶𝐶𝐶𝐶𝐴𝐴𝐶𝐶 𝑐𝑐𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑝𝑝𝐶𝐶𝐶𝐶 𝑦𝑦𝐶𝐶𝐶𝐶𝐶𝐶 𝑖𝑖𝑖𝑖 𝑡𝑡𝐶𝐶𝐶 3 𝑦𝑦𝐶𝐶𝐶𝐶𝐶𝐶 𝑝𝑝𝐶𝐶𝐶𝐶−𝑝𝑝𝐶𝐶𝐶𝐶𝑖𝑖𝑝𝑝𝑝𝑝
• also calculated index for 1 year prior, not shown in this PPT
10
0100200300400500600700800900
1000
2013-14 2014-2015 2015-2016 Post
Tota
l Cra
shes
per
Yea
rTotal Crashes, Control Segments
65 mph 55 mph
0100200300400500600700800900
1000
2013-14 2014-2015 2015-2016 Post
Tota
l Cra
shes
per
Yea
r
Total Crashes, Increased Speed Segments
Speed Increase to 70 mph Speed Increase to 65 mph
11
0
10
20
30
40
50
60
2013-14 2014-2015 2015-2016 Post
Fata
l and
Inju
ry A
Cra
shes
per
Yea
r Fatal and Injury A Crashes, Control Segments
65 mph 55 mph
0
10
20
30
40
50
60
2013-14 2014-2015 2015-2016 Post
Fata
l and
Inju
ry A
Cra
shes
per
Yea
r Fatal and Injury A Crashes, Increased Speed Segments
Speed Increase to 70 mph Speed Increase to 65 mph
12
Changes in Crash and Volumes (Index)
13
1.0
1.20
1.37
1.02
1.67
1.1
1.75
1.36
2.00
1.29
Total Monthly Volume
Total Crashes (All)
Fatal & Inj. A Crashes (All)
Total Crashes (Trucks)
Fatal & Inj. A Crashes (Trucks)
Control (65 mph) Speed Change (70 mph)
Changes in Crash and Volumes (Index)
14
1.1
1.05
1.21
0.83
0.69
1.2
1.43
1.67
1.47
1.60
Total Monthly Volume
Total Crashes (All)
Fatal & Inj. A Crashes (All)
Total Crashes (Trucks)
Fatal & Inj. A Crashes (Trucks)
Control (55 mph) Speed Change (65 mph)
Preliminary Observations• Speeds
↑ Increase in average speeds (+ 3 mph)• More vehicles traveling at higher speeds (i.e. >75 mph)
• Crashes – Speeds raised to 70 mph cars / 65 mph trucks↑ Increase in total crashes (~+382 cr/yr)• No apparent change in fatal and injury A crashes ↑ Increase in truck-involved crashes (~+140 cr/yr)• A possible decrease in truck-involved fatal injury A crashes
• Crashes – Speeds raised to 65 mph cars / 60 mph trucks↑ Increase in total crashes (~+223 cr/yr)↑ Increase in fatal and injury A crashes (~+20 cr/yr)↑ Increase in truck-involved crashes (~+37 cr/yr)↑ Increase in truck-involved fatal and injury A crashes (~+3 cr/yr)
15
Limitations of Study
• Speed analysis• ATR speed data includes trucks and some ATRs have
heavy truck volumes• ATR coverage is somewhat sparse for 2-lane segments in
Eastern Oregon• Did not look at speed differences between cars/trucks
• Safety analysis is preliminary• Method is basic and is not statistically rigorous • Control highways not ideally matched• 2017 crash data is preliminary and subject to change• Post year includes Jan 2017 and Feb 2017 (winter weather
conditions)
16
Questions
Chris Monsere, PhD, PEProfessor and Chair Department of Civil and Environmental EngineeringPortland State UniversityPhone: 503-725-9746Email: monsere@pdx.edu
17
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