Splash and Spray Measurement and Control:Recent Progress in Quebec

G. Dumas and J. Lemay

Department of mechanical engineering, Laval University, Quebec City, Canada

Summary. This paper presents results of a series of road tests measuring the sprayclouds generated by a truck/trailer traveling on a watered roadway with and with-out specifically-configured splash guards covering all the wheels. The tests wereconducted with a carefully-arranged set of laser transmissometers, and data showsignificant reductions in spray density at some fixed positions from the truck-trailerand the roadway. Data is also given showing the effect of adding a drag-reducingair shield on the truck. Emphasis is put on the full-scale test procedures and on thereliability/repeatability of the measurements.

1 Introduction

Every motorist driving regularly on highways has experienced situations ofsignificantly reduced visibility in rainy conditions while following, crossing orpassing a heavy truck. There is no doubt that such encounters can increasethe anxiety level of the drivers (cars as well as trucks) and may represent aserious road safety hazard.

Although one usually refers to the “splash and spray” as the generic phe-nomenon responsible for this adverse effect on visibility, it should be pointedout that it is more the spray clouds surrounding the heavy vehicle than thesplash itself that represents the main perturbation and inconvenience. Indeed,the splash being the part associated with the large droplets of water raisedby the tires, it tends to follow ballistic trajectory and to stay relatively closeto the ground on smooth road surfaces. Interference with motorist’s visibilityis thus minimal. On the other hand, the spray which consists of very smalldroplets of water can remain airborne for a long time and be transportedalong in the turbulent air flow. It typically produces fog clouds on each side ofthe vehicle and behind it (Fig. 1). According to previous studies such as theextensive work of Weir et al. in the 1970’s [1], the spray is formed when somewater is being atomized after impacting a hard surface under the vehicle. Ifthere is a sufficiently large air flowrate in that area, the mist being produced

534 G. Dumas and J. Lemay

Fig. 1. A mild case of reduced visibility due to the splash and spray of a typicalheavy truck.

is evacuated away before it gets a chance to reform large droplets that wouldquickly fall back to the ground.

It should be emphasized here that the formation mechanism of spray andits later dispersion involves quite complex physics and aerodynamics as wellas a large variety of parameters which can be classified as “truck-centered” or“situational” [2]. For example, in the former category, one would include thetires treads, the speed and load of the truck, its general shape and underbodydetails, while in the latter category, one would list the pavement texture, thethickness of the water film on the road, and the magnitude and direction ofthe ambient wind.

Strangely, the important progress made in the 1970’s and 1980’s on severalof these aspects has not brought us much closer to practical, real life solutionsof the splash and spray problem in the 1990’s and up to now. In our view,the main reason for that is twofold: first, no system or devices tested so farseem to provide the desired overall level of effectiveness at a minimum costand with minimal adverse effects (on the drag, the brakes, the maintenance,etc.), and second, perhaps more importantly, the lack of recent developmentturns out to be fundamentally linked to the difficulties associated with themeasurement of the phenomenon itself.

Indeed, virtually all large scale efforts in this area of research were aban-doned when in 1988, the National Highway Traffic and Safety Administration(NHTSA) announced [3] that it was terminating its pending rulemaking (or-dered in 1982) to require splash and spray suppression devices on all newtruck tractors, trailers and semitrailers because it determined that no avail-able technology had been demonstrated to

“... significantly reduce splash and spray from truck tractors, semitrailers and trail-ers, and significantly improve visibility of drivers, as demonstrated during testingon highways, at test facilities, and in laboratories to take into account possiblewind and rain conditions.” [3]

The major problem for the NHTSA was a lack of consistency and too muchvariability in the full-scale road test data that had been produced to establishthe effectiveness of a wide variety of splash and spray suppression devices and

Splash and Spray Measurement and Control 535

concepts. NHTSA’s position has remained unchanged since then as reportedin updates to Congress in 1994 [4] and 2000 [5].

All the same, the splash and spray problem has continued to bother high-way users despite the very few actual crashes that have been officially linkedto it [4]. The general public interest has nonetheless remained high as wellas the interest of the transport industry. Several national and local govern-ments in America and in Europe have thus proposed, or have been consideringproposing, some form of legislation on the question [5]. In that spirit, the De-partment of Transportation of the province of Quebec (Canada) in 1997 gavethe present authors the mandate to develop a local expertise on the splash andspray issue that could be used to carry out rigorous, repeatable comparisonsbetween existing and future anti-spray systems or devices.

Since then, two campaigns of full-scale road tests [6][7] have been realizedby the authors to develop a proper measuring technique and to compare afew basic spray suppression devices. A third experimental campaign was alsoundertaken in a small-scale wind tunnel to investigate the laboratory model-ing of spray clouds and to contribute towards a better understanding of theaerodynamic aspects of the problem [8]. This last campaign is not discussed inthis paper so as to emphasize the test procedures put forward in our two roadcampaigns, and the lessons that have been learned for better, future tests.

2 Road Test Measurements

The challenges associated with the quantitative measurement of the sprayclouds characteristics in typical highway situations are not conceptual or the-oretical issues. They are rather of a very basic, practical/economical and tech-nical nature. Repeatable conditions of crosswind and water film for instancemay be quite demanding to provide, even on a dedicated test track. So arethe parameters of speed and precise positioning of the test vehicle on the wettrack. Many passages of the test vehicle may thus be required to reduce un-certainty in the mean data, but testing budget and track schedule are oftenquite restrictive. Some compromises and optimization of the procedure haveto be devised and validated.

A valiant effort to do so and to propose a rigorous road test protocol wasinitiated in the early 1990’s by Johnson and Weir under the auspices of theSociety of Automotive Engineers. It yielded in 1994 the SAE RecommendedPractice J2245 for splash and spray evaluation [9] which synthesized almosttwo decades of R&D in the United States. To the authors’ knowledge, however,there was no report available in 1997 of its formal application in an actualroad test campaign, nor has there been since then. Some key aspects of therecommended procedure are briefly reviewed below.

2.1 SAE Recommended Practice J2245

In the SAE recommended procedure [9], two types of approach are proposed.Both of them involves stationary test setups, meaning that the test-truck isdriven through a wet test section with the measuring instruments installedon both sides of the track. An alternative setup attached to the truck hasbeen proposed in Europe [10], but it seems more appropriate for local splashmeasurements than for global spray clouds characterization that is of interesthere.

The first technique recommended in the SAE standard is called the “videodigitizing method”, and it uses large checkerboards (see Fig. 2a) and imageprocessing techniques to measure the loss of contrast when the spray cloudhappens to be between the camera and the target board. Although interestingin principle in terms of providing some discrete spatial information over entireplanes, this approach was not selected here due to the post-processing delaysinvolved and the significant crosswind sensitivity expected.

The second, and more attractive method in our opinion, is called the“laser transmissometers method” and it measures the loss of light transmis-sion through the mist, i.e., the opacity of the spray cloud. According to thestandard, two lasers are used on each side of the track (see Fig. 2) and are setat a height above the road corresponding to a typical car driver’s line of sight.The four corresponding photometers are positioned in front of the lasers atleast 15 m (50 ft) away. The signal from each of the photocell is continuouslyrecorded during the passage of the test vehicle.

Assuming here the “SAE low crosswind scenario”, i.e., crosswind compo-nent less than 5 km/hr (3 mph) during the run of a given test truck config-uration on the wet track, the procedure J2245 defines the “measurement forthat run” as being the arithmetic average of the four photocell values. Eachof the sensor measurement is expressed as a percentage of light transmittancereduction (% obscured) called “Figure of Merit” (FOM) which is calculatedas

FOM = 100×(

1− Vmin − V0

Vmax − V0

)(1)

Slope = 1%

1.14 m

0.61 m

1.52 m1.83 m

1.68 m Midpoint of Test Section60.96 m (200 ft) to end (type)

Laser Photocell

15.24 m (50 ft) min VEHICLE PATH

3.66 m (12 ft)

Anemometer(a) (b)

Fig. 2. SAE’s recommended practice J2245. (a) View from behind showing the 4lasers and the checkerboards; (b) Plan view of the test section. Adapted from [9].

536 G. Dumas and J. Lemay

where Vmax is the voltage before the passage of the vehicle (unimpeded beam),Vmin is the minimum voltage recorded during the run, and V0 is the “zerovoltage” (offset) measured when the beam is occluded. A 100% means to-tal opacity of the spray cloud while 0% means total transmittance, i.e., novisibility impairment.

In the present work, the authors have preferred to use the terminology“Opacity Index” (OI) in place of Figure of Merit to facilitate interpretationand to emphasize the difference put forward with respect to Vmin as is dis-cussed further. However, one should note for the moment that the SAE’s FOMwill correspond to the maximum instantaneous value (peak value) of the OIproposed in this work.

The overall FOM of a test truck configuration, equipped or not with ananti-spray device or system, is finally obtained according to the SAE’s stan-dard by ensemble averaging over a minimum of 8 different runs at a givenwind condition such as, for example, low head wind or low left crosswind [9].The lower the score, the better the given configuration is classified in termsof visibility impairment and safety hazard.

2.2 First Road Test Campaign

For our first road test campaign in 1997, an original technique inspired ofthe SAE’s laser method was conceived with a particular aim to provide aricher information about the lateral distribution of opacity through the spraycloud. Monotonic decay of cloud opacity with respect to lateral distance fromthe truck seemed to be taken for granted in previous works [2] leading to theSAE’s standard. It was believed by the present authors that, for the purpose ofcomparing or developing spray suppression devices, more detailed data aboutthe spatial distribution of the mist was important. Information closer to theside of the vehicle (sensors are at 1.22 and 2.13 m in SAE’s J2245; Fig. 2)was also desired since it represents a crucial visibility region for a followingmotorist in the process of deciding or not to overtake the heavy vehicle infront of him on a two-way road.

Oscillatingmirror (1.2 Hz)

Laser(He-Ne 10 mW)

Photocells

Steppingmotor

(a) (b)

Fig. 3. First road campaign in 1997. (a) Ramp of 15 sensors within their protectivetubes inside the photometers housing; (b) Laser and oscillating mirror.

Splash and Spray Measurement and Control 537

The approach that was developed and successfully implemented involveda 4 m ramp of 15 sensors distributed along its length (Fig. 3) yielding finalsensors positions from 0.76 to 4.78 m. A single laser with an oscillating mirrorwas used to produce a sweeping laser beam that illuminated at least 3 timeseach photocell while the test vehicle was moving through the central 30 m ofthe 61 m test section (200 ft between laser and sensors) at a nominal speedof 77 km/hr. A general view and sketch of this setup are provided in Fig. 4.Note that for the purpose of this paper, most details are omitted here. For allthe information concerning these tests and the results of some comparisonscarried out between a few spray suppression approaches, the reader is referredto the original technical report [6].

Typical raw signal for a given sensor is shown in Fig. 5. An “analyzingwindow” is defined so that only the part of the signals measured while thetruck is passing in the central region of the test section, away from the pertur-bation of the two protective housings, is considered to calculate the OpacityIndex denoted here OII. In that central region, it is assumed that the spraycloud carried by the test vehicle is, statistically, in its stationary state. Onethus defines the OII measured by each of the 15 photocells as

(a)

(b)

Fig. 4. Test track of the first road campaign in Blainville, Quebec. (a) General viewof the site prior to the tests; (b) Sketch of the setup about the wet track.

538 G. Dumas and J. Lemay

1

0

1

0

1

0

0 2 4 6 8 10 12

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Vwm-V0

Vnm-V0

V-V0

Time (s)

Time (s)

Time (s)

No mist signal

With mist signal

t1 t2 t3 x61x0

Original signal (sensor #4)

Extracted signals

Fig. 5. Typical sensor signal among 15 recorded during a run. The time intervalbetween t2 and t3 is the data analyzing window which corresponds to the truckentering and exiting the central 30 m between laser and sensors. The non-vanishingsignals in the unimpeded portion and in the analyzing window (clean and perturbedgaussian responses of the swept-by sensor) are then regrouped for processing.

OII = 100× Vnm − Vwm

Vnm − V0(2)

where Vnm is the maximum voltage recorded with “no mist” before the passageof the test vehicle, Vwm is the maximum voltage “with mist” in the analyzingwindow (Fig. 5), and V0 is the regularly measured offset voltage. Therefore,similarly to the SAE’s FOM , a 100% value of OII means total opacity whilea 0% value implies that there is no visibility impairment whatsoever.

(a) (b)

Fig. 6. Two of the truck configurations tested in the first campaign. (a) The“base configuration” (Base) of the 5-axle tractor-trailer test vehicle with its stan-dard European-type fenders; (b) The “reddaway configuration” (RW) of the truckequipped with some homemade Reddaway-type of fenders [1][2].

Splash and Spray Measurement and Control 539

OI I (%)

Position (m)

SAE Laser #1

SAE Laser #2

0 1 2 30

20

40

60

80

100

4 5

RWBase

Fig. 7. Example of results from the first campaign: Lateral distribution of opacityindex OII(y) at a height of 1.14 m for the base and reddaway configurations. Thelateral position y is defined from the side of the truck’s trailer. The curves plottedhere represent ensemble averages over 8 runs in each case, all under SAE’s conditionof low wind.

Plotting the opacity index data of all sensors on the ramp against thelateral position yi of each sensor – measured with respect to the actual po-sition of the test vehicle on the track for that particular run –, one obtainsthe “Lateral Distribution of Opacity” OII(y) for that given run and truckconfiguration. The distributions obtained during this first campaign for thecase of the “base truck” and for the “reddaway” configuration (Fig. 6) areshown on Fig. 7.

These results clearly suggest that simple systems such as reddaway fenderscan have measurable and positive impact on spray clouds in terms of both,their peak opacity and their spatial extent. From previous studies [1][2], onecan infer that opacity levels of 70% and above are perceived by human eyes as“very bad” (no useful visibility). One would therefore require that an efficientanti-spray device yields much lower levels (still to be determined) across thewhole width of the cloud, and in particular in the first 2 m from the side of thetruck. It is also noted from Fig. 7 (and other results of this campaign) that in-deed opacity distributions appear to be reasonably monotonic and decreasingfunctions, except perhaps very close to the vehicle.

Repeatability of the results provided by full-scale road tests being at theheart of the problem in splash and spray research, dispersion in the raw dataand statistical convergence of the final results have to be considered. First, itwas noted that the dispersion in the OII data was larger than expected: forthe base configuration, about ±12 for the inner part of the cloud (first 2 m)

540 G. Dumas and J. Lemay

and up to ±20 in the outer part (last 2 m). Large external flow intermittencemay explain in part the difference between the two regions, but it is mostlikely attributable to what has been termed the “triangle effect”, and that isdescribed on the sketch of Fig. 8. The phenomenon tends to add more noiseto the calculated indices in the outer portion of the cloud which makes itmore challenging to reach good statistical convergence, and is therefore anundesirable weakness of this approach.

In any case, significant dispersion in the OII data calculated by (2) is tobe expected due to intrinsic aerodynamics unsteady effects (air turbulenceand large-scale eddies) to which one must add the effects of varying winds(intensity and direction) between runs. Even for “low wind” conditions (UW <5 km/hr) considered here, important impact of the wind is expected as willbe addressed further. Furthermore, non-repeatability and non-uniformity inthe water film are important issues to be minimized, which was not rigorouslythe case in this first campaign where watering was provided by distributedsprinklers along the track.

Most importantly, one must realize that in this approach as well as in theSAE’s recommended procedure, the only way to improve statistical conver-gence of the final results, and thus repeatability, is by doing more runs inthe same – as much as possible – conditions. Indeed, the only averaging usedis ensemble averaging which, according to us, requires many more than the8 runs (per truck configuration) recommended and that were realized here.Four times as many runs would reduce uncertainty of the mean distributionsby a factor of two which may be viewed as a minimum. Considering differentwind conditions – as many as 8 according to the SAE’s classification – as wellas different speeds of the test vehicle and different depths of the water film,would add up quickly to prohibitive proportions in terms of both time andtesting cost.

Fig. 8. Exaggerated sketch showing the “triangle effect” that contributes to addnoise in the readings of the sensors which are not directly in front of the lasersource. While the truck moves through the central part of the test section (analyzingwindow, 31 m), and considering a given photocell on the ramp, this effect yieldsvarying optical paths of the laser beam with respect to the cloud.

Splash and Spray Measurement and Control 541

A procedure that could offer faster statistical convergence was imposingitself as a necessity to achieve dependable and repeatable full-scale road testresults. Including some temporal averaging in the process, in addition to theexisting ensemble averaging, appeared as the only practical option available toincrease convergence, and thus repeatability of the results while maintainingthe number of runs at a reasonable level. This idea as well as some significantimprovement as far as the water film is concerned were implemented in theprocedure developed for our second road test campaign.

2.3 Second Road Test Campaign

For our second campaign in 1999 (see [7] for a detailed report), we used asmall test track in the region of Quebec City. The track had a fairly uniform1% slope across the pavement which allowed us to produce a quite uniformand repeatable film of water (Fig. 9a), 1.5 mm thick, over the entire 61 m(200 ft) of the test section. A 4-inch perforated pipe running along the track

(a)

Wet pavement

61 m (200 ft)

Perforated pipe

Lasers Photocells

Downstream trigger Upstream trigger

(b)

Fig. 9. Second road campaign. (a) Upstream view of the test track and of thecontinuously fed water film; (b) Sketch of the setup about the wet track.

542 G. Dumas and J. Lemay

(a) (b)

Fig. 10. Second road campaign setup at run time. (a) Upstream view showing the3 lasers at the forefront; (b) Downstream view with the 3 photocells at the forefront.

and fed by a regulated fire hydrant was used to that end. For all practicalpurposes, contribution of the water film to the final dispersion of the datawas reduced to negligible proportion.

In this campaign, in order to eliminate the undesirable “triangle effect”and to provide for some temporal averaging of the signals, each photocellused had to have its own dedicated laser aligned with it, in much the sameway as in the SAE’s recommended practice J2245 discussed previously. Thecontinuous signal recorded for each sensor while the test vehicle is passingthrough the “analyzing window” would permit the temporal averaging needed,which departs in a fundamental way from the standard J2245. Based on theresults of the first campaign – relatively monotonic decay of lateral opacitydistributions – it appeared that three sensors (Fig. 9b) would be sufficientto properly characterize the opacity distribution. The positions retained wereselected as: 0.61, 1.22 and 2.44 m (2, 4 and 8 ft; nominal values w/r to theside of the vehicle’s trailer). This reduced number of photocells allowed to getrid of the large and perturbing protecting housings of the first campaign ascan be seen on the pictures of Fig. 10.

Typical signals recorded at run time by the three photocells are shownon Fig. 11. Note that sensor #1 is the inner one, closest to the truck, while#3 is the outer one at 2.44 m (8 ft) which would correspond to the middleof the neighbor lane next to the truck’s lane. The data indicates that theouter part of the spray cloud takes about just under 59 m (193 ft) to buildup from zero and stabilizes. Of course, wetting of the track upstream of thetest section would easily fix this problem. This is unfortunate in the spirit ofthe present method since it severely limits the time window over which onecan average the signals (assuming a common window for the 3 sensors). Thelast 0.10 second (last 2 m) before the vehicle started exiting the test sectionhas usually been selected in this campaign.

Nonetheless, this modest temporal averaging, combined with the usualensemble averaging, can significantly improve convergence of the mean results,

Splash and Spray Measurement and Control 543

0 1 2 3 4 5

Sensor # 1

Sensor # 2

Sensor # 3

Trigger

V

Time (s)

0.5

0

0

0

0

0.5

1

0.5

2

4

Entering Exiting

61 m = 3 seconds

Fig. 11. Signals recorded for each of the 3 sensors and the triggers during a typicalrun of the second road campaign.

even though dispersion itself may still remain important, as can be seen inFig. 12. In this campaign, one now defines the OI measured by each of the 3photocells in a given run as

OI = 100× V be − V ss

V be − V0

(3)

where V be is the mean voltage recorded “before entering” the wet test sec-tion (with no mist), and V ss is the mean voltage in the “stationary signal”zone (averaging time window; see Fig. 11). The results obtained for the basetruck configuration (same tractor and similar trailer as in campaign one) arepresented in Fig. 12.

The uncertainty bars shown in Fig. 12 suggest an accuracy of about ±5points on the mean opacity indices which is already a significant improvementwith respect to our first campaign, and previous works in general in this field.Only 14 runs have been necessary to achieve this level of confidence thanksmainly to the temporal averaging added to the process here – admittedlyquite modest in this instance. Longer time windows exhibiting statisticallystationary signals (Fig. 11) would allow for better temporal means whichwould tend to reduce even more the dispersion in the OI data, thus improvingfurther the confidence level of the final values. Of course, complete eliminationof dispersion in the OI from run to run is not possible due mainly to the wind’seffects. Note finally that by eliminating the “triangle effect” present in the firstcampaign, the level of dispersion in the data is now much more uniform acrossthe width of the cloud.

544 G. Dumas and J. Lemay

0 1 2 3

Mean OI

0

20

40

60

80

100OI (%)

Position (m)

OI Eq. (3)

Fig. 12. Raw results of the Opacity Index OI according to (3) for the base truckconfiguration in the second road campaign (“low crosswind” runs). The 95% con-fidence bands of the three mean values are also shown. The line connecting thesevalues is only suggestive of the actual distribution of opacity.

Our second road campaign also provided the opportunity to test the effectof a simple drag shield installed on the tractor cab. As expected, such airshield tends to keep the mist closer to the truck thus increasing opacity inthat area. However, combined with conventional anti-spray systems such asreddaway fenders, it tends to improve their performances in the mid and outerportion of the cloud as can be inferred from the results presented in Fig. 13.

(a)

(b)

Fig. 13. (a) Mean opacity results from the second campaign for the RW (reddaway)versus the AS-RW (air shield + RW) configuration – low wind condition, V = 70km/hr; (b) Test vehicle equipped with a basic air shield on the tractor cab andreddaway-type of fenders on the trailer.

Splash and Spray Measurement and Control 545

3 Recommendations for Future Road Test Campaigns

The experience gained from our two road campaigns can be summarized bythe following recommendations:

1. The general guidelines provided in the SAE Recommended Practice J2245[9] should be followed, granted the modifications outlined below.

2. Three laser transmissometers should be used on each side of the track with2 of them within the first 1.2 m (4 ft) from the side of the test vehicle (seeFig. 14).

3. The distance between lasers and sensors (test section) should be of about3 truck lengths, 61m (200 ft) in this case, to allow for proper temporalaveraging of the signals.

4. An extra 60 m or so of wet pavement should be provided upstream of thetest section to assure that statistically stationary conditions (stationaryclouds) are reached at the entrance of the test section.

Assuming, conservatively, a total span of the clouds of about 2 trucklengths, as suggested on Fig. 14, the above recommendations would allowfor temporal averaging of the signals for at least one full “truck time scale”(T = L/V ), i.e., over the last truck length of the test section. This trans-lates in this case as about 1 second of time-averaging window – ten timesas much as was permitted in the second road campaign of this work. It isexpected that such an approach, coupled with ensemble averaging over about15 “similar runs” (in terms of wind conditions, truck speed and water depth),should yield spray measurements confidence within a few percent, and thuscircumvent the basic criticism raised by the NHTSA since 1988.

Fig. 14. Sketches of approximate spray cloud envelopes under no wind condition(left), and under some “low crosswind” condition, e.g., UW " 4 km/hr (right).

There remains the challenge of how to properly take into account the effectof crosswinds in the overall evaluation of spray suppression devices. It seemsto these authors that a finer grading system than the one proposed in theSAE’s procedure is required. As suggested in Fig. 14b, it takes very littlecrosswind to significantly alter the distribution of spray around the vehicle.This represents a critical issue which still needs to be addressed.

546 G. Dumas and J. Lemay

Acknowledgement

The authors would like to acknowledge the financial support of the Min-istere des Transports du Quebec, contracts MTQ/1220-97-RG01 and 1220-98-RG02. Help and encouragement from the project manager at DoT, M.Mario Bussieres, is also gratefully acknowledged. Special thanks to the wel-coming and professional staff of the CFTC (Centre de Formation en Transportde Charlesbourg; www.cftc.qc.ca) where our second road campaign was re-alized.

References

1. Weir DH, Strange JF, Heffley RK (1978) Reduction of Adverse AerodynamicEffects of Large Trucks. Technical Report FHWA-RD-79-84, Federal HighwayAdministration, USA

2. Weir DH (1980) Truck Splash and Spray – Full Scale Tests and AlleviationDevices. AIAA Paper 80-0203, 18th Aerospace Sciences Meeting, Pasadena,CA, 14-16 January, 1980

3. NHTSA (1988) Splash and Spray Suppression Devices – 49 CFR Part 584:Termination of rulemaking. May 25, 1988. U.S. Federal Register, Vol. 53, No.101: 18861-18868

4. NHTSA (1994) Splash and Spray Suppression: Technological Developments inthe Design and Testing of Spray Reduction Devices for Heavy Trucks. Reportto Congress March 1994, National Highway Traffic and Safety Administration,U.S. Dept. of Transportation

5. NHTSA (2000) Update on the Status of Splash and Spray Suppression Tech-nology for Large Trucks. Report to Congress March 2000, National HighwayTraffic and Safety Administration, U.S. Dept. of Transportation

6. Dumas G, Lemay J, et. al. (1998) Comparative evaluation of splash guardsystems for heavy vehicles (in French; English translation also available). Con-tract report MTQ 1220-97-RG01 for the Quebec Dept. of Transport, April 1998,Fluid Mechanics Laboratory, Laval University, Quebec City

7. Dumas G, Lemay J (2000) Study of spray cloud reduction on heavy trucks byaerodynamic control: Part I – Full-scale road tests (in French). Contract reportMTQ 1220-98-RG02 for the Quebec Dept. of Transport, March 2000, FluidMechanics Laboratory, Laval University, Quebec City

8. Dumas G, Lemay J (2002) Study of spray cloud reduction on heavy trucks byaerodynamic control: Part II – Wind tunnel tests (in French). Contract reportMTQ 1220-98-RG02 for the Quebec Dept. of Transport, January 2002, FluidMechanics Laboratory, Laval University, Quebec City

9. Johnson WA, Weir DH (1994) Recommended Practice for Splash and SprayEvaluation. 1996 SAE Handbook, Vol. 3, SAE Recommended Practice J2245

10. Hucho WH (1998) Aerodynamics of Road Vehicles, 4th ed., Section 9.7.4, SAEInternational, Warrendale, Pennsylvania

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