Effect of Pavement Type and Condition on the Fuel Consumption of Vehicles

Transcription

1 28 Transportation Research Record lono Effect of Pavement Type and Condition on the Fel Consmption of Vehicles CHRISTO J. BESTER ABSTRACT The effect of pavement type and condition (roghness) on the rolling resistance of vehicles is investigated. By means of the relation beteen the energy reqirements and the fel consmption of vehicles, this effect is sed to predict the fel se on different pavements. It is fond that, except for gravel srfaces, pavement type has a minor effect on fel consmption. Roghness, hoever, correlates strongly ith rolling resistance and therefore ith vehicle fel consmption. This is important for the economic jstification of major road maintenance projects. resistances that mst be overcome by the energy spplied by the engine are: - Rolling resistance, Rr; - Air resistance, Ra; and - Gradient resistance, Rg Energy is also sed to overcome transmission losses and the internal friction of the engi ne. If (A + BV 2 )M,.5PCoAFV 2, and MgG, then the fel consmption at constant speed is: (1) As a reslt of to oil crises in the past 1 years, the impoi"tance of the fel consmption of vehicles cannot be overemphasied. Fel has strategic importance. Moreover, its cost rose to sch an extent that it not only cased high inflation rates, bt also seriosly affected the balance of payments of importing contries. Becase fel is high on the list of expenses of the vehicle oner, savings in fel consmption play a major role in the economic jstification of ne road projects. In the past, this as sally the case here geometric improvements ere being considered. There is little information available from hich the effect of pavement improvements on fel consmption can be predicted, yet sch predictions are imperative for the evalation of major maintenance operations. Becase of the nmeros variables that affect fel consmption, it is difficlt to isolate the specific effect of pavement type and condition Cl> This is mainly becase the effect is rather small (2). It as ther efore d ecided to determine the relationship beteen the p avement type and condition and the rolling resistance of vehicles. This relationship can then be sed to predict the effect on fel consmption. A procedre for determining the rolling resistance of vehicles, hich is then related to the type and condition of the pavement, is described. The latter is expressed in terms of road roghness as measred by a Linear Displacement Integrator (LDI) This road roghness vale can also be related to the qarter car index (QI) scale developed in Brail <ll. From the rolli ng resistance, the fel consmption of the test vehicles is then predicted by means of the relationship beteen the energy reqirements and fel se of a vehicle. FUEL CONSUMPTION AND ENERGY REQUIREMENTS OF VEHICLES It has been shon that the fel consmption of a vehicle is directly related to the energy necessary for the movement of the vehicle (_!). The different here rolling resi~tance (N), air resistance (N), gradient resistance (N), fel consmption (mt/km), v speed (m/ s), G = gradient (m/m), Pl bam/n, p 2 /v = idling fel consmption (mt/km), p3 (bbm +.5bpCoAF)/n, P4 = bmg/n, b fel conversion factor (mi/kj), A,B = rolling resistance coefficients, M = mass (kg), n drive-line efficiency, p air density (kg/m'), c aerodynamic drag coefficient, AF frontal projec ted area (m 2 ), and g gravitational acceleration (m/s 2 ). It is clear that the pavement type and condition can only affect fel consmption throgh the rolling resistance and therefore throgh p 1 and p 3 in Eqation 1. ROLLING RESISTANCE TESTS Theoretical Backgrond The combined effect of air and rolling resistance can be determined by sing a coasting vehicle (that is, a vehicle rnning freely, ith the engine disengaged) (5). Unde r t hese circmstances, there are only three forces acti ng on the vehicle: - Rolling resistance, - Air resistance, and - Gradient resistance. From Neton: Ma = R, + R, + Rg (2)

2 Bester 29 here a represents deceleration (m/s 2 ). Therefore and a= (A+ gg) + (B +.5 pc AF/M)V 2 (4) here This is of the form: C1 =A+ gg (6) and To determine the rolling resistance of a vehicle, the speed is measred at reglar intervals (for example, every 1 seconds) dring coasting, starting from a maximm speed on a relatively flat section of road ith a constant gradient. This is done for both directions. If the decelerations are plotted against the sqare of the speeds, the vales of c 1 and c 2 in Eqation 5 can be obtained throgh a linear regression analysis for both directions. The rolling resistance coefficient A is then eqal to the average of the to vales of c 1, and the difference beteen the to vales is eqal to 2gG. The rolling and air resistance coefficients contained in C2 cannot be calclated separately. Hoever, if the vale of c 2 differs for different road srfaces, it mst be as a reslt of a change in the vale of B, becase the air resistance is a constant. An example of this procedre is shon in Figre 1 for the test car on section 1. The eqations for the north- and sothbond tests ere: Northbond a= , V 2 (r =.992) Sothbond a= , V 2 (r=.997) (3) (5) (7) the rolling resistance co From the vales of c 1, efficient A = ( )/2 and the gradient G = ( N/kg.946)/(2 x 9.81) =.6 m/m. The last vale is the same as that given in the constrction plans for that specific section of road. If the vale of B from Bester (4) is assmed, the aerodynamic drag coefficient can be calclated from the average of the to vales of c 2 In this case: B = M = AF p = 6.86 x 1-5 m kg 2.3 m kg/m' (at an above sea level) Therefore, from Eqation 7: CD (C2 - B)M/(.5pAF).386. Test Procedres altitde of 15 m To determine the effect of road roghness and pavement type on the rolling resistance of vehicles, eight different road sections ere chosen for the tests. Each section had to have a sfficient length (±4 m) of niform gradient and roghness. The pavements on hich sections ere chosen ere as follos: to ere of asphaltic concrete, one as a portland cement concrete pavement, for had srface treatments, and one as npaved. The roghness of each section as determined by sing a Linear Displacement Integrator (LDI) developed by the National Institte for Transport and Road Research. These roghness vales cold be related to the QI scale throgh the correlation developed by Visser (!l The details of the test sections are given in Table 1. To vehicles ere sed for the tests--a passenger car and a trck ith respective masses of 1322 and 72 kg. The passenger car as fitted ith radial tires and the trck as fitted ith cross-ply tires. Both vehicles ere instrmented to yield accrate speed measrements at fixed time intervals. For reliable reslts, the tests had to be condcted in indless conditions, ith the correct tire N<n. 5 ' E I- <! D:'. x SOUTH - BOUND o NORTH-BOUND O FIGURE I L-~~~~~~-'-~~~~~~~J._~~~~~~-'-~~~~~~~ I SQUARE OF SPEED I m/sl 2 Deceleration verss sqare of speed dring coasting.

3 3 Transportation Research Record 1 TABLE 1 Details of Test Sections Roghness Section Length No. Pavement Type (m) LDI QI" l A>phaltic concrete Asphallic concrete Concrete Srface treatment Srface treatment 6 l Srface treatment 5 l Srface treatment Unsrfaced 35 3, QI = LOI from Visser (6). pressre and ith the tires having been ell armedp in advance. Becase of the limited length of the test sections, all tests had to be repeated ith different initial speeds to cover a fll range of speeds. Test Reslts The speed of the vehicles dring coasting as determined at 1-second intervals. From these speeds, the deceleration over the interval and the average speed dring the interval ere calclated. Linear regress ion analyses (see Eqation 5) ere then performed for both directions of each test section. The average vales for both directions are given in Table 2 for the passenger car and in Table 3 for the trck. Trck For all roads: A= I 82R (N/kg) (r =.984) C 2 =3.4 x 1-4 (m- 1 ) (IO) here R represents road roghness in m/km as measred by the LDI. These relations hips are shon in Figres 2, 3, and 4. Discssion The roghness of paved roads has an effect, althogh small, on the rolling resistance coefficients of a passenger car. Unpaved roads have a mch greater effect. For a trck, hoever, only the constant rolling resistance coefficient, A, shos a meaningfl relat1onsnip itn road roghness. From Figres 2, 3, and 4 it appears that concrete and asphaltic concrete pavements have (for cars and trcks) a loer rolling resistance than roads ith a srface treatment. These differences, hoever, are small and ill be disregarded in frther calclations. It shold be mentioned that concrete and asphaltic concrete pavements ith rogher srfaces ere not available in the vicinity of Pretoria. ROLLING RESISTANCE AND FUEL CONSUMPTION From Eqations l and 7: TABLE 2 Test Reslts for Passenger Cars Section Roghness A C2 No. LDl(m/km) (N/kg) (o.1-4 m- 1 ) , S,41i9.964 By sing the folloing vales of constants for typical Soth African vehicles, the total fel consmption at constant speed can be calclated for the to test vehicles (ll: b =.85 mi/kj (for cars ith petrol engines).7 m1/kj (for trcks ith diesel engines) n =.9 (for cars).86 (for trcks) P2 45 ml/looos (for cars) = 6 mll/ los (f or trcksj. TABLE 3 Test Reslts for Trcks Section Roghness A B No. LDI (m/km) (N/kg) (O.J-4m-') Passenger Car On srfaced roads: F = R + 45/V + ( R)V G. On the npaved road (gravel road) tested (Roghness = 3.53 m/km): F = /V +.683V G. From these vales, the folloing relationships beteen road roghness and the varios coefficients ere established: Trck On all roads: Passenger car For all srface roads: A= R (N/kg) C2 = ( R) x 1-4 (m-1) (r =.965) (r =.884) (8) (9) F = l.67r + 6/V +.178V 2 here F = R = v G = + 575G fel consmption (ml/km), road roghness (m/km) as measred by the LDI, speed (m/s), and gradient (m/m)

4 Bester 31 "" "' ' <!.2 f-- E ~.1 a: (,!) ::::; a: 2 tj. o D ASPHALTIC CONCRETE CONCRETE ROUGHNESS (m/km) FROM LDI SURFACE TREATMENT GRAVEL SURFACE FIGURE 2 Rolling resistance coefficient, A, verss road roghness for test car. 3 4.,- Q 'E N 5. ~ f-- ii: lj._ tj. o D ASPHALTIC CONCRETE CONCRETE SURFACE TREATMENT GRAVEL SURFACE Note that on negative gradients the minimm fel consmption is p 2 /V. When V=O, the distance-based fel consmption, as in Eqation 1, old be infinite and the time-based idling fel consmption is eqal to p 2 /l (m2/s) These formlas can no be sed to determine the savings in fel consmption that ill reslt from improving the condition of pavements, either by ne constrction or by rehabilitation. So, for instance, if the pavement condition is improved from R = 3. to R =.6 m/km, the fel saving ill be 321 liters/year/km for an annal average daily traffic of 1, vehicles per day inclding 2 percent heavy vehicles. Figres 5 and 6 sho the fel consmption of the test vehicles for different road conditions. CONCLUSIONS ROUGHHNESS (m /km) FROM LDI FIGURE 3 Speed-related coefficient, C2, verss road roghness for test car. l. The pavement type has a small effect on the rolling resistance and, therefore, on the fel consmption of vehicles. 2. Both the constant and speed-related rolling resistance coefficients for passenger cars are affected by the condition (roghness) of the pavement. 3. At 8 km/h, a passenger car can se 29 percent more fel on a gravel road than on a paved road <! 2 f-- G: lj._ ~.1 f- tj. ASPHALTIC CONCRETE a: o SURFACE TREATMENT (,!) o GRAVEL SURFACE ::::; a: o._~~~~~~-'-~~~~~~~'-~~~~~~-'-~~~~~~~ ROUGHNESS (m/km) FROM FIGURE 4 Rolling resistance coefficient, A, verss road roghness for test trck. LDI

5 32 Transportation Research Record 1 1 in good condition. It shold, hoever, be remembered that loer speeds are maintained on gravel roads. 4. Only the constant rolling resistance coefficient for trcks is affected by the condition of the pavement. ~. At 8 km/h, a trck can se 18 pprcent more fel on a gravel road than on a paved road in good condition. E -" -.._ 75 ACKNOWLEDGEMENT E i== a.. :::;; (/) LL ROUGHNE SS = 6 m / km This paper is pblished ith the permission of the Chief Director of the National Institte for Transport and Road Research, Concil for Scientific and Indstrial Research, Pretoria, Repblic of Soth Africa. REFERENCES SPEED! km / h ) FIG URE 5 Fel consmption of test car nder different road conditions. ~ ~ E 2 f:= a.. :::;; (/) o ci 1 LL ROUGHNESS. 6 m/ km SPEED (km/ h) FIGURE 6 Fel consmption of test trck nder different road conditions G. Morosik and s.. Abaynayaka. Vehicle Operating Costs in the Caribbean: An Experimental Stdy of Vehicle Performance. Laboratory Report 156. Transport and Road Research Laboratory, Crothorne, Berkshire, England, J.P. Zanieski. Fel Consmption Related to Roaday Characteristics. In Transportation Research Record 91, TRB, Natio~l Research Concil, Washington. n.c pp C.A.V. Qeiro. Calibrating Response-Type Roghness Measrement Systems Throgh Road-and-Level Profiles. In Transportation Research Record 898, TRB, National Research Concil, Washington, D.C., 1983, pp C.J. Bester. Fel Consmption on Congested Freeays. In Transportation Research Record 81, TRB, National Research Concil, Washington, D.C., 1981, pp A.D, St. John and D.R. Kobett. Grade Effects on Traffic Flo Stability and Capacity. NCHRP Report 185, TRB, National Research Concil, Washington, D.C., 1978, 11 pp. 6. A.T. Visser. A Correlation stdy of Roghness Measrements With an I ndex Obtained From ~ 'R~nr.trl Profile Measred ith Rod and Level. Technical Report RC/2/82. National Institte for Transport and Road Research, Concil for Scientific and Indstrial Research, Pretoria, Repblic of Soth Africa, C.J. Bester. Fel Consmption of Highay Traffic. Ph.D. dissertation. University of Pretoria, Pretoria, Repblic of Soth Africa, 1981.

6 38 Transportation Research Record 1 ACKNOWLEDGMENT This paper is based on a research stdy condcted at the Pennsylvania Transportation Institte, Pennsylvania State University, nder partial sponsorship of the Pennsylvania Department of Transportation. A fll discssion of the stdy may be fond in the final report for the project. REFERENCES 1. J.R. Ingram. Friction of Pennsylvania The Effects of Road Roghness on the a Slipping Tire. M.S. thesis. The State University, University Park, 2. B.E. Qinn and s.e. Hildebrand. Effect of Road Roghness on Vehicle Steering. Highay Research Record 471, HRB, National Research Concil, Washington, D.C., 1973, pp F.J. Benvin. The Redesign of a Circlar Track Apparats for Traction Testing ith Steering and Braking. Master of Engineering Paper. The Pennsylvania State University, University Park, K.T. Cheng. Instrmentation and Data Processing System for Dynamic Tire Force Measrement. Report in Mechanical Engineering. The Pennsylvania State University, University Park, 198. The contents of this paper reflect the vies of the athors, ho are responsible for the facts and the accracy of the data presented herein. The contents do not necessarily reflect the official policy of the Pennsylvania Department of Transportation. Abridgment Effect of Vehicle and Driver Characteristics on the Psychological Evalation of Road Roghness M. S. JANOFF and J. B. NICK ABSTRACT The objective of this paper is to smmarie the reslts of an experiment that evalated the effects of vehicle sie, vehicle speed, residence of rating panel, and training of rating panel on the sbjective evalation of road roghness. The reslts of the panel ratings indicated that there as no significant effect of the different vehicle sies or vehicle speeds sed on the sbjective evalation of road roghness, and that trained raters (i.e., experts) evalated roads the same as ntrained raters (i.e., laymen). A small bt significant effect of panel residence as fond. EXPERIMENTAL PROTOCOL AND DATA COLLECTION All test sections ere selected, marked, and formed into to rotes--one in Pennsylvania and one in Florida. Each section as then measred ith a Mays Ride Meter. Panel members, in grops of three or six, ere given detailed instrctions on ho to rate and then ere driven over the rote to individally rate each section's ride qality. Mean panel ratings ere compted from the individal ratings for each test section for each panel. TABLE 1 Smmary of Experimental Plan All panel ratings sed the Weaver/AASHO scale employed in previos research l!l Five panels of 21 licensed drivers each--for of Pennsylvania residents and one of Florida residents--ere sed to obtain the sbjective ratings. To grops of bitminos test sections--34 in Pennsylvania and 31 in Florida--that span a ide range of roghness ere selected for the stdy. Table 1 smmaries the experimental plan and Table 2 provides an overvie of the kev variables and the hypotheses that ere tested. The test sections spanned a range of roghness from 28 to 639 in. per mile. Rating Scale Panel Sites Vehicles Vehicle speeds Panel instrctions Weaver/ AASHO 63 Pennsylvania-licensed drivers (3 grops of 21 each) 21 Florida-licensed drivers 21 Florida experts 34 in Pennsylvania 3 1 in Florida 2 Pennsylvania K-cars 2 Florida K-cars 1 Pennsylvania sbcompact car One per site eqal to the operating speed of the site (except for a sbset sed in the vehicle speed experiment) Given niformly to all sbjects