1. Morris Smith
Study of Sign Characteristics on I-20
January-May 2014
CEE 2699
Dr. Yichang Tsai

2. I. Introduction
The overall objectiveof thisresearchprojectistoassessandimprove the effectivenessof the usage
of LiDARpointcloudtechnologytoautomaticallydetectandinventorytrafficsigns. Thismethodof sign
inventory,if provensuccessful,wouldbe aconsiderable advance insignmanagementandtechnology.
Trafficsignsare a seeminglysmall yet vital componentof astable infrastructure.All of the different
typesof signsare meantto conveysimple andunderstandable messagestodriversinordertokeep
themfocusedonthe road. Thishelpstopromote safetysuchthat accidentsmaybe prevented,
especiallyonhighways,where caraccidentshave amuch higherfatalityrate thanotherroads. One way
for trafficcontrollersandengineerstostudythe efficiencyof these signsistotake an inventoryinwhich
GPS coordinatesandsigntype are considered,andthisiswhy automaticsigndetectionwouldgoa long
waytowards maintainingsustainable infrastructure.
II. Data Extraction
Before testingthe LiDARpointcloud onInterstate 20 inGeorgia,a groundtruth was neededtoserve
as the control in whichto compare itwith.Thiswas createdbymanuallyinventoryingsignsusingthe
Trimble Spatial ImagingAnalyst interface.Anapproachwastakensimilartohow a licensedtraffic
engineerwouldtake intermsof the typesof signsto be inventoried.All signswithincertainconstraints
were considered;those thatwere notwere temporarysigns,guardrail markers,electronicsigns,and
signson the right-of-wayonanentrance/exitramp.
a. Productivity
The entire setfromwhichdata was extractedcoversapproximately200 milesfromAlabamato
SouthCarolina,eastboundandwestbound.There are 136,016 framesintotal inthe set, so 400 milesof
data yieldsanaverage of 340 framespermile.The total numberof inventoriedsignsis3,847, and ittook
approximately20 hoursto collectall of them.Thisyieldsaproductivityof 3.21 signsperminute,and
113.35 framesperminute.Itishelpful toconsiderthe signdistributionalongthe highway;the highest
concentrationof trafficsignswasfoundinurbanareas and suburbanareasas well as segmentsof the
highwaythatwere underconstructionduringdatacollection.A large portionof the highway,however,
wentthroughrural areasand had sparselydistributedsigns,includingmanysectionsthatjustconsisted
of mile markersalone.
b. Pros and Cons of Data Extraction
Establishingagroundtruthdatasethad bothpositive andnegative impactsonthe overall
project.The mainreasonbehindcreatingthe groundtruthwasto provide a defaultcontrol datasetin
whichto compare LiDARresultswith.A helpful aspectof the setwasthatit had coordinatesforevery
signwithwhicha researchercouldcompare withthe correspondingsignthatwasdetectedthrough
LiDARanalysis. Thiswouldbe veryadvantageoustoanyone whowouldwanttotake a strictlyanalytical
approach to improvingthe parameters.Preliminarydataextractionwouldalsoallow new userstothe
LiDARsoftware toaccustom themselvestothe interface.
On the otherhand,the extractionof the groundtruth data was verytediousandtime-
consuming.Itisalsoimportantto note several hoursof researchwere lostduringthisphase due to
severe weatherconditions;thispushedbackthe LiDARanalysismanyweeks,andthe primaryobjective
inwhichthe projectwas aimedforwasrushedand couldonlybe carriedout ina muchshorterperiodof
time thanwhat wasdesired.

3. c. Issues
Three issuesinparticularwere encounteredmultipletimesduringdataextraction.The firstone
was thatoverheadsigns,mostlyroadname signs,were particularlydifficulttoaccuratelypinpointusing
the two-clicktriangulationmethod.Secondly,large vehiclessuchastrucks occasionallyblockedasign
that wason the lefthandside of the cameravan. Lastly,datapointson an opposite boundappearedto
be inaccurate.The last issue isessentiallyanobservationanddoesnotaffectthe overall project.
d. Recommendations
For future usersof thismethodof data extraction,itisrecommendedtoinventorysignsbased
on predictingwhetherornotthe LiDAR detectionwill pickitup.People whoare selectedforthiskindof
researchshouldhave anample amountof intuitiontodeduce whetherasignisbig andreflective
enoughtobe detected.Itisunderstoodthatthisprojectisfortestpurposesandwill notbe usedbyany
departmentof transportationtostudysignplacement.
III. LiDAR-Based Sign Detection
Onlyone clip(AlabamatoGeorgia,Eastbound) wasusedfortestingthe LiDARdetection.There are
five particularparametersthatwere considered whenevaluatingthe effectiveness.These are the
sensitivity,minimumelevation,the minimumdistance fromsigntosign,the maximumlateral distance,
and the minimumhitcount.Those thatwere notconsideredwere parametersthatmeasuredthe height
and widthof the signs.
a. Method of parametric study
The methodwhichwasusedto evaluate the effectivenessof the signdetectionwasabasic
visual analysis.Afterrunningthe LiDARtool,signdetectionmarkerswerecomparedwithgroundtruth
markerswithrespecttotheirlocations.The effectivenessof the parametersetwasevaluatedbasedon
whatsignsmatchedthe ground truthset,whichonesdidnot,how manymarkerswere placedateach
sign,etc.The resultswouldbe comparedforaboutone quarterof the clip,so that general assumptions
couldbe made about the rest of the data.
b. Observations
The issue that wasrun intothe most while testingthe LiDAR parameterswasthatthere were
multiple detectionmarkersatmanylarge signs.The initial conclusionwasthatthe tool was considering
the largersignsas more than one and essentiallycountedthemasmultiplesignsinextremelyclose
proximity.Inresponse,the minimumdistance fromsigntosignwasdecreasedforotherdatasets.This
decreasedthe numberof markersona decentnumberof signs.Afterwards,arealizationcame thatthe
large numberof markerswas verylikely aresultof ahighamount of reflectivityonthe signs.Afterthat
realization,the minimumhitcountwasincreased,andthe resultsshowedasignificantimprovementin
bringingthe amountof markersfor eachsignto one.
c. Recommendations
One parameterthatdealsspecificallywithreflectivenessthatcouldbe probedisthe sensitivity.
There couldbe much more analysisputintothisparameter,anditis highlysuggestedforwhomever
may pickthisprojectup to dosuch analysis.Alsorecommendedistoinclude aLiDARcamera forthe left-

4. handside of the road andcreate more clipsforthat; there maybe parameters thatare completely
differentthanthatof those of the right that wouldyieldoptimal performance.