Transcript Document 7559346

Assessing Winter Storm-Related NonRecurring Congestion in the Salt Lake Valley
Ralph Patterson1, Randy Graham2, Kevin Barjenbruch2, Glen Merrill2, Glenn
Blackwelder1, Brett Hansen3, Mike Holts3, Julie Miller1, Mike Seaman2, Jeff Williams3,
Audra Yocom1, Carol Werner4
1Utah
Dept of Transportation, Traffic Operation Center, Salt Lake City
2National Weather Service, Salt Lake City
3NorthWest Weathernet, Salt Lake City
4University of Utah, Salt Lake City
AMS WAF/NWP Meeting – Omaha, NE
Outline
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Partners

Weather Impacts on Roads in
the Salt Lake City metro

Comparison of travel impacts
associated with two winter
weather events
Photo courtesy UDOT
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Future work
AMS WAF/NWP Meeting – Omaha, NE
Unique Collaboration

Federal (NWS), state (UDOT), and
private meteorologists (Northwest
WeatherNet), academia (University
of Utah)
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Meteorologists embedded at the
UDOT Traffic Operations Center
(TOC)
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Meteorologists with UDOT and
Northwest WeatherNet
Direct involvement of UDOT
Traffic Engineer
AMS WAF/NWP Meeting – Omaha, NE
Increased Demands…Increased
Commute Times

Rapid population growth

23.5% increase between 2000 and 2008

Increased demand on existing infrastructure

Congestion results in annual cost of $250
million in Utah (UDOT)

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Recurring (i.e., AM/PM peak commute times)
Non-recurring congestion (weather, accidents)
Inclement weather plays a significant role in
non-recurring congestion

Delays, mobility, productivity, and safety

“Large weather events cause trips to take 4050% longer” (UDOT report)
Photo courtesy UDOT
AMS WAF/NWP Meeting – Omaha, NE
So…
Which event will produce the
biggest impact?
A. 1-3” between 200 PM - 600 PM
B. 4-6” between 1000 PM - 400 AM
C. 6-8” between Noon - 1000 PM
AMS WAF/NWP Meeting – Omaha, NE
Factors in Event Impact
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Time of day
Day of week
Snowfall rates
Snowfall amounts
Road temperatures
Mitigation strategies
Holidays
Public perception/preparedness
AMS WAF/NWP Meeting – Omaha, NE
Weather Impact on Commute
“This is a striking finding – but it seemed intuitive on further consideration. The only things
Travel Time Index (TTI)
Example
– Measure
commute
of the
of increase
20 minutes
in travel time associated
that affect theHigh
entireTTI
road (congestion
system around Salt
Lake
Citydominated
are snowstorms,
orweather
major holidays.
and
delays)
by
with congestion,
TTI of incidents
1congestion)
= 20 minutes
and
Other sources of delay (crashes,
thunderstorms,
tend weather.
to be more localized.” (UDOT)
TTI of 1.3 = 20 x 1.3 = 26 minutes
Image courtesy Glenn Blackwelder
AMS WAF/NWP Meeting – Omaha, NE
Data…Data…Data…
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~20 events from the winter 2008-09’
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Collection of weather and traffic data
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Radar and satellite data
Mesonet observations
Road temperatures
Traffic information
Plow driver reports
Accident information
Investigation of NWS and UDOT
statements
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Discussion of societal impacts
Does lead time impact volume?
AMS WAF/NWP Meeting – Omaha, NE
Tracking Impact
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Performance Management
System (PeMS)
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240 sensors in the SLC Metro
High temporal (5 min) and
spatial resolution (1/2 mile)
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Vehicle Miles Traveled (VMT)
Vehicle Hours Traveled (VHT)
Flow
Speed
Delays
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Accident Information
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Plow Driver Reports
AMS WAF/NWP Meeting – Omaha, NE
5 Jan 2009 –
Well forecast….but

1-3” forecast for Salt Lake Valley prior
to onset
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Winter Weather Advisory issued near
onset
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Verified well
Based on potential impacts on the
afternoon commute
Minimal discussion of impact in days
leading up to event

Several significant storms had preceded this
event
Photo courtesy KSL-TV
Road Considerations and Impacts
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Road temperatures in the low
to mid 20s F
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5 Jan 2009 - Road temperatures
~ 420 PM MST
Snow stuck to roads at onset

??Limited mitigation prior to
event??
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Over 180 accidents in Salt
Lake and Utah Counties alone
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Worst commute of the season
AMS WAF/NWP Meeting – Omaha, NE
19 December 2009
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More ‘ramp-up’ to the event
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Watch issued 36 hours before onset
Winter Storm Warning issued ~21 hours before onset
Area Forecast Discussion – 442 PM 17 Dec 2008 …With very cold temps expect snow to rapidly accumulate on
area roadways…
Winter Storm Warning – 302 PM 18 Dec 2008
…Snow expected to rapidly accumulate along area roadways
and result in treacherous driving conditions…
..Much of this snow may be occurring during the late afternoon
and early hours which would have a very significant impact on
the evening commute…
Add image
Road Considerations and Impacts
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Roads temperatures remained
near 30 degrees through the
event
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19 Dec 2008 - Road temperatures
~ 400 PM MST
More effective mitigation

Level of service remained
higher throughout the event
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Aggressive mitigation prior to
and during event
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3-7” storm total
AMS WAF/NWP Meeting – Omaha, NE
Speed and Flow
I-15 SB 8600s Snow Event (1/5/09)
9000
8000
7000
6000
Mean Flow
5000
Event Flow
4000
Event Speed * 100
3000
2000
1000
8:
00
10
:0
0
12
:0
0
14
:0
0
16
:0
0
18
:0
0
20
:0
0
22
:0
0
6:
00
4:
00
2:
00
0:
00
0
Time of Day
I-15 SB 8600s Snow Event (12/19/08)
10000
9000
8000
7000
5000
4000
3000
2000
1000
0
0:
00
2:
00
4:
00
6:
00
8:
00
10
:0
0
12
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0
14
:0
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16
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22
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Flow
6000
Mean Flow
Event Flow
Event Speed * 100
th Event between the two
January
A
lot of 5similarities
 events…
Speed trough on the 5th was lower
 Drop
in discretionary
travel
 Bigger
event
 Travel
is notflow
displaced
 Reduced
due to in time (i.e.,
flowcongestion…reduced
doesn’t recover) capacity of
system due to slow travel?
 Speeds and flow drop off rapidly
right after onset
December 19th Event
 Increase in flow (above normal)
prior to snowfall onset
 Well forecast onset?
 Dip right at peak traditional max
flow time due to increase in
snowfall intensity
Level
of
Service
(LOS)
Freeway level of service is defined by the density of vehicles on the road (vehicles
per mile per lane), and is a measure of a driver's freedom to maneuver

LOS A - Free flow - the ability to maneuver is unimpeded
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LOS B - Reasonably free flow - slight restriction in maneuverability
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LOS C - Ability to pass or change lanes is not always assured, but posted speed is
maintained, more driver vigilance required
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LOS D - Slight reduction in speeds, ability to pass or change lanes reduced, traffic
stream has little space to avoid disruption, driver comfort reduced
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LOS E - Ability to pass or change lanes is constrained, flow is unstable, speed
varies, road is at capacity, drivers are uncomfortable
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LOS F - A breakdown in vehicular flow - each vehicle follows another at minimum
safe spacing due to demand exceeding capacity.
AMS WAF/NWP Meeting – Omaha, NE
So, how was the
commute?
th event:
December
January
5th 19
event:
 Higher
Note
level
significant
of service
difference
indicates
Fridaythe
afternoon
is typically
a
between
that
people
Mon
areand
moving
Tue Monday
(albeit at a
heavier
commute
than
reduced speed, in this case)
afternoon
 As flow goes down there is high
density
Flow
and
speed packed
showed
similar
Not completely
of vehicles
on theon
roadway
the
trends,
but driver
perception of 19
roads there
is spacing
December
likely to
very
 No space,commute
very difficult
switch
different
thanbetween
5move
January
commute
lanes,
Difference
vehicles
inThu
lock
and
step,
Fri is
frequent
not
that significant
stops
 Better
prepared?
More effective
mitigation?
AMS WAF/NWP Meeting – Omaha, NE
Uncertainty and Impact
Meteorology
Road Conditions
“This is also an encouraging finding because it suggests that the
It is important to note that one of the most cost effective solutions for
highest overall delay mayImpact
be predictable (but perhaps not
mitigation of the congestion problem is driver habit modification. –
avoidable) with accurate weather forecasts.” –
UDOT
UDOT 2007 Congestion Report
Public Response
AMS WAF/NWP Meeting – Omaha, NE

Human Behavior
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Future Work
With confidence in forecast and road impact,
can we influence response?
Effective communication strategies?
Increased penalty for false alarms?
Project with NWS/UDOT/NWN and
University of Utah - Winter of 09-10’
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Two to three events
~400 professionally administered driver surveys
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Levels of awareness
Sources of information
Responses to road/weather info (behavior
modification)
Detailed correlation of weather to travel impacts
Weather Enterprise impact statements
AMS WAF/NWP Meeting – Omaha, NE