The Pothole Patrol: Using a Mobile Sensor Network for Road
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Transcript The Pothole Patrol: Using a Mobile Sensor Network for Road
The Pothole Patrol: Using a
Mobile Sensor Network for
Road Surface Monitoring
Jakob Eriksson, Lewis Girod, Bret Hull, Ryan
Newton, Samuel Madden, Hari Balakrishnan
MIT Computer Science and Artificial Intelligence
Laboratory
Outline
Introduction
Architecture
Data Acquisition
Algorithm
Performance
Related Work
Discussion
P2 : A mobile road surface monitoring system
Hazardous to drivers and increasing repair costs due to
vehicle damage
Determine “which” roads need to be fixed
Static sensors will not do well – requires mobility!
P2 is first of its kind
Challenge : differentiate potholes from other road
anomalies (railroad crossings, expansion joints)
Challenge : coping with variations in detecting the same
pothole. (speed, sensor orientation)
P2 successfully detects most potholes
data)
(>90% accuracy on test
2
P
Architecture
Vehicles have GPS and 3-axis accelerometer
<time,location,speed,heading,3-axis acceleration>
Opportunistic WiFi/Cellular connections with dPipe
to cope network outages
Taxi Testbed
7 Toyota Priuses1
Soekris 48012 Embedded Linux
Wifi Card
Sprint EVDO Rev A3 Network card
GPS
Some numerical facts
9730 total kms
2492 distinct kms
7 cabs
174 km with >10 repeated passes
1
2
3
1.
2.
3.
http://www.carbuyersnotebook.com/archives/Toyota_Pruis_2006.jpg
http://www.pkgbox.org/Soekris-4801.jpg
http://gizmodo.com/gadgets/peripherals/two-new-sprint-evdo-rev-a-cards-pantech-px500-and-sierra-wireless-aircard-595-200423.php
2
P
Architecture
Pothole
Record
Clustering
Central Server
Cab 1
GPS
Location
Interpolator
3 Axis
Accelero
meter
Pothole
Detector
Cab 2
GPS
Location
Interpolator
3 Axis
Accelero
meter
Pothole
Detector
2
P
Architecture
Distance Traveled vs. Total Hours
Segments of roads that were
repeatedly covered
Across All Taxis
Lower line represents unique roads
258,021 unique road segments
DATA ACQUISITION
Accelerometer
placement
Dashboard
Windshield
Embedded Computer
GPS Accuracy
Standard deviation 3.3m
DATA ACQUISITION
Hand Labeled Data
Smooth Road
Crosswalks/Expansion
Joints
Railroad crossing
Potholes
Manholes
Hard Stop
Turn
DATA ACQUISITION
Loosely Labeled
Training Data
We know only types of
anomalies and their
rough frequencies
Exact numbers and
locations are unknown
Extends available
training set
ALGORITHM
Features of accelerometer data
High energy events are potholes?
Not really!
Rail road crossings, expansion joints, door
slamming are high energy events
Accelerometer data is processed by
embedded computer
256-sample windows
Pass through 5 different filters
ALGORITHM - Filtering
speed vs.
z ratio
OUT
Pothole
Detections
IN
Windows
of all event
classes
Speed
Input
Raw accelerometer data
256-sample windows
High-pass
xz-ratio
z-peak
ALGORITHM - Filtering
speed vs.
z ratio
OUT
Pothole
Detections
IN
Windows
of all event
classes
Speed
High-pass
Speed
Car is not moving or moving slowly
Rejects door slam and curb ramp events
xz-ratio
z-peak
ALGORITHM - Filtering
speed vs.
z ratio
OUT
Pothole
Detections
IN
Windows
of all event
classes
Speed
xz-ratio
High-pass
High-Pass
Removes low-freq components in x and z axes
Filters out events like turning, veering, braking.
z-peak
ALGORITHM - Filtering
speed vs.
z ratio
OUT
Pothole
Detections
IN
Windows
of all event
classes
Speed
High-pass
xz-ratio
z-peak
z-peak
Prime characteristic for significant anomalies
Rejects all windows with absolute z-acceleration < tz
ALGORITHM - Filtering
speed vs.
z ratio
OUT
Pothole
Detections
IN
Windows
of all event
classes
Speed
High-pass
xz-ratio
z-peak
xz- ratio
Assumes potholes impact only side of the vehicle
Identifies anomalies that span width of the road (rail crossings,
speed bumps)
Rejects all windows with
xpeak within Δw (=32) samples from zpeak < tx X zpeak
Or, ( Xpeak/ zpeak )< tx
ALGORITHM - Filtering
speed vs.
z ratio
OUT
Pothole
Detections
IN
Windows
of all event
classes
Speed
High-pass
xz-ratio
z-peak
speed vs. z ratio
At high speeds, small anomalies cause high peak accelerations
Rejects windows where Zpeak < ts X speed
or, (Zpeak /speed ) < ts
ALGORITHM – Sample Traces
ALGORITHM - Training
Tuning parameters t={tz,tx,ts} are computed
using exhaustive search over a set of values
For each set t, we compute detector score
s(t) = corr – incorr2
Corr is no. of pothole detections when
sample was labeled as “pothole”
Maximize s(t)
Include loosely labeled data
s(t) = corr – incorr2labeled – max(0,incorrloose – countr)
ALGORITHM - Clustering
Improve accuracy
Cluster of at least k events must happen in the
same location with small margin of error(Δd)
Clustering algorithm
Place each detection in Δd X Δd grid.
Compute pairwise distances in same or neighboring grid
cells
Iteratively merge pairs of distances in order of distance
Max intra cluster distance < Δt
Reported location is the centroid of the locations within it
ALGORITHM – Blacklisting &
False Negatives
Well-known anomalies like bridges, railroad
crossings, speed bumps etc can be located
from GIS sources and blacklisted
GPS errors
Pothole avoidance
Biased detection will focus on critical
anomalies
PERFORMANCE EVALUATION
Goals
Minimize false negative rate for smooth roads
Never a flag a smooth road as anomaly
Missing a few potholes is acceptable
Evaluation
1.
2.
3.
4.
Classification accuracy on hand-labeled data
Performance improvement using loosely labeled
data
Performance on loosely labeled roads
Spot-checks
PERFORMANCE EVALUATION
Performance on Labeled Data
Randomly divided into training set and test set
Class
Hand Labeled
w/ Loosely Labeled
Pothole
88.9%
92.4%
Manhole
0.3%
0.0%
Expansion joints
2.7%
0.3%
Railroad Crossing
8.1%
7.3%
False positive rate is 7.6%
Not accurate
PERFORMANCE EVALUATION
Estimating the false-positive rate
Ran the detector on loosely labeled roads
Road
# potholes
# windows
# detections
rate
Storrow Dr.
few
1865
3
0.16%
Memorial Dr.
few
1781
2
0.12%
Hwy I-93
few
2877
5
0.17%
Binney St.
some
6887
25
0.63%
Beacham St.
many
1643
231
14%
Helps set upper bound on false positive rate (at most 0.15%)
on good roads.
PERFORMANCE EVALUATION
Impact of features and thresholds
1. Only Z peak
2. w. xz-ratio filter
3. w. speed vs.
z ratio
tx=1.5
tx=2.5
ts=5
PERFORMANCE EVALUATION
Performance under uncontrolled conditions
Slamming doors
Fiddling with the sensor equipment
Driving behaviors
Deliberately avoiding potholes
Use clustering
k=4
PERFORMANCE EVALUATION
Spot Checks
Typical pothole
Manhole
Expansion joint
RELATED WORK
Surveys
Falling weight deflectometer
Machine vision – cameras, robots
Accelerometer
Microsoft Trafficsense – smartphones
DISCUSSION
This is what I think
Innovative
Ground truth establishment is tedious, expensive in dense
road networks
Will it work in hilly areas ,slopes?
Future work?
Driver feedback – Interactive embedded computers
Smartphones – Cheaper solution, greater coverage
Comments/Questions ???
REFERENCES
The Pothole Patrol: Using a Mobile Sensor Network for
Road Surface Monitoring Jakob Eriksson, Lewis Girod, Bret Hull, Ryan Newton,
Samuel Madden, Hari Balakrishnan MIT Computer Science and Artificial Intelligence
Laboratory
U. Lee, E. Magistretti, B. Zhou, M. Gerla, P. Bellavista, and A. Corradi. MobEyes:
Smart Mobs for Urban Monitoring with a Vehicular Sensor Network. IEEE Wireless
Communications, 2006.
TrafficSense: Rich Monitoring of Road and Traffic Conditions using Mobile
Smartphones Prashanth Mohan, Venkata N. Padmanabhan, and Ramachandran
Ramjee {prmohan,padmanab,ramjee}@microsoft.com Microsoft Research India,
Bangalore
http://research.microsoft.com/apps/pubs/default.aspx?id=70573