4B.4IMPACTS OF CLIMATE CHANGE AND WEATHER ON COMMERCIAL MOTOR VEHICLES

Michael A. Rossetti*

Volpe National Transportation Systems Center, Cambridge, MA

Michael Johnsen

Federal Motor Carrier Safety Administration

1. BACKGROUND

Observed climatic patterns represent the averagesand variability of long term weather conditions. Thesepatterns result from the interactions of oceanic,geologic, and solar influences, the atmosphericconcentrations of various gases and aerosols, and otherfactors. Various studies now indicate that the planet isgetting warmer and that this global warming isbeginning to impact regional weather patterns and thusweather-sensitive sectors of the economy (AMS 2007).As part of these impacts, climate change can produceboth economic gains and losses (IPCC 2007 andChangnon 2005).

Commercial motor vehicles (CMVs) include truckswith a gross vehicle weight rating of >10,001 lbs, aswell as most types of buses. The study period for whichCMV data are available is 1975 to the present.Exposure to adverse weather may occur at any point indistribution supply chain and cause ripple effects in theintermodal transportation system. This paper looks at aspecific problem area from the transportation sector,the role of different types of weather events as riskfactors in CMV crashes and performance. This includesthe possible role of climate change in increasing thedistribution, frequency or severity of those weatherevents and their impacts on measures such as safetyand delay.

The Federal Motor Carrier Administration (FMCSA)sponsored this work as part of its responsibilities toreduce the number and severity of CMV crashes andenhance the efficiency of CMV operations. Through anunderstanding of the how weather and climate forcesaffect CMV safety, the FMCSA hopes to address futurerisks posed by climate variability and climate change.Since FMCSA’s primary mission is to reduce large truckand bus crashes and fatalities, FMCSA has beenanalyzing how crashes occur, but has never heavilyinvestigated the role of weather in these crashes. The

* Corresponding author address: Michael A. Rossetti,RTV-4A, Volpe National Transportation Systems Center,55 Broadway, Cambridge, MA 02142: e-mail:rossetti@volpe.dot.gov.

FMCSA needs to know the trends and factors inweather-related CMV crashes, and also if actionswithin its jurisdictional realm (e.g., driver training,truck technologies, highway alerts) can be taken toreduce weather-related crashes. These are inaddition to external programs such as improvedobservation and detection systems, more accurateand precise models, and better weather forecasts.

2. PROFILE OF CMV ACTVITY IN THE U.S.

There are now over 9 million CMVs registeredin the U.S., most of which are large trucks. From1975 to 2005, CMV registrations increased by 60percent, while vehicle miles traveled (VMT) grew by163 percent (Figure 1). Combined with similarincreases in automobile VMT, and virtually nogrowth in highway capacity, congestion hasbecome a serious problem on the nation’s roadsystem. From a weather perspective, CMVs andtheir operators face a variety of weather-relatedexposure risks.

Figure 1 - Commercial Motor VehicleRegistrations and VMT, 1975-2005

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The impacts on safety from the combination ofcongestion and weather exposure is of concern to theFMCSA as it pertains to how climate change couldamplify some of those effects in its long-term planninghorizon by increasing the frequency or intensity ofsevere weather. Commodities carried by CMVs are ofgreat economic importance. Recent data indicate thattrucking as a single mode, or as part of intermodalcombinations, accounts for about 80 percent of the totalvalue of $13 trillion for all commodity shipments in theU.S, and 42 percent of all ton-miles. CMVs share aninfrastructure that includes 47,000 miles of Interstates,115,000 miles of NHS roads, and 3.8 million miles ofother roads (DOT/RITA 2006). The Federal HighwayAdministration (FHWA) estimates that about 25 percentof non-recurrent delays on freeways are due toweather, and that weather-related delay adds $3.4billion to freight costs annually (Maccubbin 2002).

3. WEATHER AND CLIMATE FACTORS IN CMVOPERATIONS

Weather is one of many determinants of truckcrashes, along with socioeconomic and demographicfactors, speed, alcohol, driver error, vehiclecharacteristics, etc. In addition, average temperatureshave been found to show a positive association withvehicle deaths, and precipitation a negative association(Loeb 2007). Although only about 16 percent of all fatalCMV crashes are associated with adverse weather orwet pavement, that share can still have significanteffects on vehicle performance and safety as wellsystemic effects that may impact other modes andeconomic sectors. In addition, FMCSA may have lessinfluence in reducing weather-related crashes.

Specific types of short term weather conditionsaffect CMVs crash conditions, driver decision making,dispatchers, and state highway officials. Climateimpacts include the longer term effects on safety,infrastructure and vehicles of larger, more frequent ormore intense storms, precipitation and winds, extremesof temperature, and other factors.

Weather conditions affect CMVs by degradingsafety, performance and capacity and can changeshipping patterns and methods. Over a long period oftime, climate patterns could affect CVM operations byimpacting intermodal infrastructure and operations,vehicle components, drivers, and the underlyingproduction patterns of agricultural and other industrialshipments. The U.S. Department of Transportation willsoon publish a report indicating significant threats to theGulf Coast of the U.S. from increased sea-level rise,subsidence and storm surges (U.S. DOT 2007).Although climate change may adversely affecttransportation and CMVs, certain types of regimes mayproduce benefits. For example, by producing tranquilweather over the northern U.S., and as a stimulus to

consumer spending, the major El Nino event of1997-1998 may have increased profits by up to 8percent in the trucking and airline industries(Changnon 1999).

The transportation infrastructure relevant toCMVs includes all modes associated with theintermodal supply chain: highways, rail, air andwater. This includes all activities related to thetransportation of goods, and reflects a weather-sensitive supply chain that extends from rawmaterials, to suppliers, manufacturers, wholesalers,retailers, and consumers (Figure 2).

GoodsProducers Carriers Intermodal

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Figure 2 – Typical Supply Chain

These effects may occur en route or at specificnodes. In addition, because of growing modalinterdependence, weather events may produceripple effects and disrupt supply chains.Manufacturers and producers may have productiondelays due to employees unable to reach their jobsduring bad weather, or because of delays in theshipment of intermediate goods needed forproduction. Carriers may lose speed, routingefficiency, and the ability to meet schedules forintermodal transfers. Consignees experiencedelays, or do not receive finished goods andsupplies. Tight synchronization between productionand delivery schedules to handle just-in-time (JIT)delivery practices may create an environmentincreasingly vulnerable to the effects of weatherand climate.

Weather events hazardous to CMVs can rangefrom wet pavement, rain, winter storms, icing,temperature extremes, floods, hurricanes, highwinds and severe thunderstorms to more routineevents such as solar glare, poor visibility and lightrainfall. Some specific types of impacts are asfollows:

Rainfall, Wet Pavements, and Flooding –Rainfall and wet pavements are the most commontype of adverse weather that affects CMVs; over 60percent of all weather-related fatalities occur inrainy conditions. Rainfall causes delays andincreased risks of collisions with other vehicles andhighway structures. It induces loss of control dueto acceleration from wheel spinning andhydroplaning. The initial onset of rain may mixwith preexisting road oils to produce slippery

conditions. Rain reduces braking performance, resultingin increased stopping distances and more frequentskidding; wet roads can double stopping distances.

Rainfall also reduces visibility and can make itharder to see clearly, especially at night. Wet surfacesproduce similar effects on vehicles and their driverseven if skies are not currently causing rainfall. Evenafter rain stops, it may take 30 minutes or more beforepavement begins to dry. Wet conditions may persist fora longer time under certain types of atmospheric andsoil moisture conditions, from melting snow banks, fromprevious snow falling from other vehicles, and floodingepisodes.

Widespread flooding in major rivers may result inwholesale rerouting of shipments. Problems posed byhigh waters from flash floods, river floods, persistentheavy rains, and hurricanes are sometimes a significantconcern for CMVs. Wet brakes may weaken or applyunevenly. Floods also can also make roads and bridgesimpassable or produce complete washouts that requireclosures and rerouting. Re-routing around floodedareas increases VMT and the likelihood of additionalCMV crashes. Coastal flooding accompanied by wavebattering caused by large storms is a threat to roadinfrastructure. Effects like these may gradually becomemore amplified if sea levels rise as projected by climatemodels The Gulf Coast study (DOT 2007) tentativelyprojects that relative sea-level in the Gulf Coast areamay increase at least one foot during the next 50-100years.

Snow and Icing - Heavy snow causes delays, roadclosures, loss of traction, loss of visibility, and otherdriver control problems. Surface temperatures onbridges and ramps cool more rapidly than thesurrounding roadbeds, producing hazardous local icingconditions and resultant property damage. Freezingrain, black ice and light frozen precipitation glaze roadsas temperatures fall over a short period. Winterconditions also place additional stress on CMVcomponents such as the cooling system, defrosting andheating equipment, wipers and washers, tires andchains, windows and mirrors, hand holds and deckplates, radiator shutters and exhaust systems. Manystates require large trucks to carry and use tire chainsas snow conditions warrant.

Fog and Visibility - CMVs have significantvulnerability to fog and poor visibility. Impaired visibilitymay result from intense storms, coastal and ground fog,smog, dust, precipitation-induced road spray and solarglare. Dense fog may form overnight in low-lying areason highways resulting in reduced speeds, sudden lossesof control and increased risks of collisions betweenvehicles and roadside structures. Lowered visibilityposes a safety risk to truckers and increases the risk ofdamage in the event of collision. Fog events have the

potential for large, multi vehicle accidents. Signsand signals may become more difficult to see, thusleading to human error. Reduced visibility alsoincreases the potential for schedule delays.

Strong Winds - Strong winds and cross windscan disrupt CMV operations. High profile trucks aresusceptible to potential vehicle instability, loss ofcontrol and blowovers from crosswinds in exposedareas such as bridges, interstate highways andmountain passes. Expected peak wind gusts mayalso play a role in determining the maximum windspeed in which a heavy truck can safely drive.

Temperature Extremes – Prolonged episodes ofheat and cold can impact both the safety andperformance characteristics of CMVs. Extremelycold temperatures can affect the operation ofvehicle engines, tires, mechanical and hydraulicsystems. Hot weather can cause tar in the roadpavement to rise and result in slippery surfaceconditions. Certain types of livestock carried bytrucks are very sensitive to excessive heat and cold.Other types of commodities are perishable andtemperature-sensitive, requiring protection from theexternal conditions.

Drought - Droughts affect transportationdirectly and indirectly. They promote conditionsthat result in forest fires that may produce smokedense enough to cause delays and road closures.Dry conditions combined with strong winds canlower visibility from airborne dust and sand. Verydry conditions may lower yields on agriculturalcommodities and thus impact the demand fortrucking.

Drought conditions may also impact CMVsthrough their effects on intermodal connections.Low water causes barges to run aground, resultingin delayed shipments of coal, chemicals, agriculturalgoods produced by manufacturing plants in thatregion. Shipments may be diverted from one modeto another. The summer of 2005, for example,produced such conditions over part of theMidwestern U.S., lowering water levels on theMississippi, Missouri and Ohio rivers.

4. CMV WEATHER-RELATED CRASHES

The National Highway Traffic SafetyAdministration (NHTSA 2007) maintains a completecensus of fatal crash data called the Fatal AccidentReporting System (FARS). FARS includes crashdata CMVs and other vehicles that are collectedfrom reports filed by police investigators at thescene. FARS data can be queried for “atmosphericconditions.” Codes include:

1 No Adverse Atmospheric Conditions2 Rain3 Sleet (Hail)4 Snow5 Fog6 Rain and Fog7 Sleet and Fog8 Other (Smog, Smoke, Blowing Sand, Dust)9 Unknown

FARS does not include any weather-related crashesassociated with high winds. FARS also reports roadsurface conditions with the following codes:

1 Dry2 Wet3 Snow or Slush4 Ice5 Sand, Dirt, Oil8 Other9 Unknown

In this study, “weather-related crashes” refer to allcrashes coded with all combinations of atmospheric androad surface conditions that indicated either adverseweather or road surfaces that were wet, snowy, or icy.

Large trucks account for 3.4% of all vehicleregistrations, 7.5% of VMT and 11.1% of fatal crashes.CMVs are over-represented in fatal crash data. Otherstudies show similar results (Braver et al 2002). Theseries of six charts displayed in Figure 3 shows thetrend of specific types of weather elements associatedwith fatal CMV crashes. Rain, snow, fog and wetpavement are the four main associations. The raw dataindicate a slight decreasing trend over the period forrain, snow and fog, as well as for total weather-relatedcrashes. The series for snow and fog show slightlymore volatility. This may reflect short term climatevariability, such as exceptionally snowy winters in theeastern U.S.; 1996 is such an example.

Wet pavement crashes have shown little trend formany years. A 1980 study by the NationalTransportation Safety Board (NTSB) found that 13.5percent of all fatal accidents occurred on wet pavement,while precipitation occurred only about 3.0 to 3.5percent of the time nationwide. This indicates that fatalaccidents on wet pavement occur 3.9 to 4.5 times moreoften than might be expected, and that the wet-pavement accident problem should be of concern to allStates (NTSB 1980). Other studies have noted thepersistent problem of wet pavement exposure to driversand the seeming lack of appreciation for its risks (cite).

Normalized by VMT, the trend of fatal, weather-related CMV crashes shows a distinct downtrend, fallingby about half from 1975-2006. The long-term trendmay be indicative of the effects of many forces, such asbenefits stemming from the National Weather Service’smodernization program, advances in weather forecasts,

vehicular improvements and technology, theintroduction of intelligent transportation system(ITS) features, changes in CMV traffic patterns, orpossibly changes in the frequency or distribution ofweather events. Additionally, because this studyincluded only fatal crashes, the same trend may ormay not apply to non-fatal, weather-relatedcrashes.

Since about 2002, the decline in fatal crasheshas leveled off (Figure 4). This may indicate thatthere could be a minimum number of weather-related crashes that will occur over which theFMCSA and other agencies have little control orthat weather events that contribute to CMV crashesare becoming more frequent or severe, or areaffecting a larger number of CMVs.

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Figure 4 – Fatal Large Truck Crashes vs.Fatal, Weather-related Large Truck Crashes,

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Figure 5 shows the distribution of CMV fatalcrash sites by latitude/longitude for the period2004-2006. Icons show the type of weatherreported by the police report. (FARS data haveincluded lat/lon information since 2001). The mapshows the expected higher frequencies of snow andsleet-related crashes in the northern and mountainstates, fog in the Appalachian region, and rain inthe southern tier of states.

Wet pavement crashes (with fair weatherreported) are more evenly distributed throughoutthe county. Overall, the map shows a highconcentration of fatal CMV crashes in the majorinterstate corridors of the East and Midwest, and inCalifornia. The segment of Interstate 80 that runsfrom New Jersey to Iowa shows a particularly highnumber of weather-related crashes, a likelycombination of traffic volume and its exposure toadverse weather conditions throughout the year.

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Figure 3 – Fatal, Weather-related CMV Crashes by Type of Weather Event, 1975-2006, with 5-year Moving Averages

Figure 5 - Locations of Fatal Crashes involving Commercial Motor Vehicles,by type of Weather Event, 2004-2006

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Figure 6 - Trends in Mean Annual Temperatureand Precipitation, 1900-2002

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Figure 7 - Weather and Climate Events, Hypothetical Forecast Likelihood andLead Times Required by Commercial Motor Vehicles

5. REGIONAL PROJECTIONS OF CLIMATECHANGE AND POTENTIAL IMPLICATIONS

Although the reliability of regional scale climate andweather predictions is still low, and the degree to whichclimate variability may increase remains uncertain,potentially serious changes have been identified. Thesechanges have the potential to affect the frequency andintensity of extreme weather events, regionaldistributions of temperature and precipitation, stormtracks, and sea levels). Results from the U.S. ClimateChange Science Program (CCSP 2007) report onWeather and Climate Extremes under Climate Changewill soon provide a better understanding about thepotential and actual increases in storm events.

Trends in mean annual temperature and indicate asteady rise since the late 1970s (Figure 6). A similaruptrend seems evident for mean annual precipitation.Vulnerability of the national highway system CMVs toclimate change arises from potential exposure to bothunforeseen and secular changes in weather or climatepatterns and from potential increases in the intensityand frequency of extreme weather events.

Relevant to transportation and CMV impacts, theNational Assessment Report (USGCRP 2000) outlinedvarious climate change scenarios for different U.S.regions. Table 1 summarizes these scenarios and liststhe potential impact on CMV operations. The IPCCC, inits recently issued Fourth Assessment Report (IPCC2007), makes similar but more broadly basedprojections for the 21st century based on the SpecialReport on Emission Scenarios (SRES).

Under those scenarios, there should be a mixedbag of benefits and losses for CMVs. Warmer wintersshould simulate greater consumer spending and providea boost to the manufacture of both producer andconsumer goods. Those same conditions will favormore business and generally provide fewer weatherimpediments and improved safety margins to theshipment and delivery of those commodities throughoutthe transportation system.

On the other hand, various studies also project anincrease in extreme or large events, such as higherincidences of flooding, larger and more intensesnowstorms, and increased levels of severethunderstorms (Trapp et al 2007). Although these mayoccur relatively less frequently, such high-impact stormscould decrease CMV safety and performance undersome scenarios.

The types of weather events that currently impactCMV safety and operations will require continuedvigilance by the FMCSA, the industry, traffic managers,and other interested parties. It is important to advanceefforts to reduce the lead time needed to avoid or

mitigate the impacts of those events on relevanttime scales, ranging from the very short term to thepossible time scales of climate change, to (Figure7). Climate change scenarios could possiblyenhance or diminish the impacts of some of theevents illustrated. Accordingly, concerns such assafety, inspections, maintenance, operations, andcapital investment depend on the ability of theFMCSA and CMV fleet operators to acquire and actappropriately upon this information.

6. FMCSA STRATEGIES FOR A CHANGINGCLIMATE

The FMCSA is examining the trends and factorsin weather-related CMV crashes, and also if actionswithin its jurisdictional realm can be taken toreduce weather-related crashes. One strategymight include driver training and educationprograms aimed at operating CMVs in inclementand occasionally extreme weather conditions. Theagency could also consider expanded research intothe role of human factors in responding to adverseweather conditions, and in the delivery to and useof weather information by vehicle drivers

Another part of this approach could includemodifications or waivers to existing CMV rulesFMCSA rules currently limit the number of hours ofservice permitted for CMV drivers. There areexceptions based on extenuating weatherconditions. In addition, individual states sometimesgrant temporary waivers, for example when driversare hauling relief supplies into a flood-stricken area.

Other contributions to the solution includeadvanced truck technologies and telematicsequipment. The FMCSA could also look atimproved information programs aimed at CMVmanufacturers to build in processes and equipmentto respond to changes in climate regimes andweather conditions. Strategic opportunities existfor the FMCSA to improve the capability of CMVsand drivers to adapt to the type of weatherconditions and climate regimes now projected bythe CCSP, IPCC and others

7. CONCLUSIONS

This paper examined different types of weatherevents as risk factors in commercial motor vehicle(CMV) crashes and performance, including thepossible role of climate change in increasing thedistribution, frequency, or severity of those weatherevents. To the extent that CMVs are an integralpart of an intermodal transportation system, thesefindings may also extend to other modes oftransportation such as railroads, and marine.

Table 1 - USGRP Climate Scenarios and Potential Impacts on Commercial Motor Vehicles

Overall fatal weather-related crash data from theFARS system shows a declining trend from 1975 to thepresent, with a recent leveling off. This trend providesencouragement to efforts to make highway travel lesssensitive to adverse weather, although GIS data showpocket of persistent clusters of weather-related crashesalong certain corridors or within specific regions of thecountry. The concern is that under scenarios of climatechange, the conditions that give rise to these weatherevents may cause less safe driving conditions.

.The FMCSA can address these concerns and

promote safety though a combination of education andtraining programs, the introduction of vehicle telematicsequipment, and working with the carrier industry andmanufacturers to build in processes and equipment forresponding to changes in climate patterns and weatherconditions.

Benefits of CMV weather and climate informationinclude improved safety, improved decision making forrouting and scheduling, and better performance for thevehicle, driver and infrastructure, better information forforensic investigation and crash event reconstruction,enhanced research, training, and education, moreaccurate economic impact analysis, and more insightfulresearch into the role human factors.

The FARS database has only recently includedgeospatial data as part of the police reports. As thiscache of information continues to grow, there will beexcellent opportunities to coordinate with NCDC climateand storms databases. The NCDC, for example, nowhas under development a Severe Weather DataInventory (SWDI).

Climate variability and climate change, changes intransportation management and vehicle technology, andchanges in infrastructure, may bring about futureoperating environments different than those of the past.CMV carriers, dispatchers and drivers will have access toenhanced information on weather conditions, and howsuch conditions may impact their vehicles, generaltraffic conditions, road surfaces, and driver responses tovarious weather phenomena. This accessibility can befully realized through better dissemination technology,better training, and protocols that improve the skill ofdrivers in adverse weather and wet pavement.

If climate change results in more frequent orintense storms affecting commercial motor vehicles, thehistoric decline in weather-related crashes may level off(as may be currently occurring) or start to increasewhich would pose significant challenges to FMCSA’sprimary mission in reducing CMV fatalities and crashes.Because weather-related crashes may be difficult forFMCSA to influence, this could indicate that FMCSA mayneed to explore more aggressive or creative strategiesfor reducing weather-related crashes.

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